Living in two worlds: the plant and insect lifestyles of Xylella fastidiosa.

PubMed

Chatterjee, Subhadeep; Almeida, Rodrigo P P; Lindow, Steven

2008-01-01

Diseases caused by Xylella fastidiosa have attained great importance worldwide as the pathogen and its insect vectors have been disseminated. Since this is the first plant pathogenic bacterium for which a complete genome sequence was determined, much progress has been made in understanding the process by which it spreads within the xylem vessels of susceptible plants as well as the traits that contribute to its acquisition and transmission by sharpshooter vectors. Although this pathogen shares many similarities with Xanthomonas species, such as its use of a small fatty acid signal molecule to coordinate virulence gene expression, the traits that it utilizes to cause disease and the manner in which they are regulated differ substantially from those of related plant pathogens. Its complex lifestyle as both a plant and insect colonist involves traits that are in conflict with these stages, thus apparently necessitating the use of a gene regulatory scheme that allows cells expressing different traits to co-occur in the plant.

Exserohilum rostratum: characterization of a cross-kingdom pathogen of plants and humans.

PubMed

Sharma, Kalpana; Goss, Erica M; Dickstein, Ellen R; Smith, Matthew E; Johnson, Judith A; Southwick, Frederick S; van Bruggen, Ariena H C

2014-01-01

Pathogen host shifts represent a major source of new infectious diseases. There are several examples of cross-genus host jumps that have caused catastrophic epidemics in animal and plant species worldwide. Cross-kingdom jumps are rare, and are often associated with nosocomial infections. Here we provide an example of human-mediated cross-kingdom jumping of Exserohilum rostratum isolated from a patient who had received a corticosteroid injection and died of fungal meningitis in a Florida hospital in 2012. The clinical isolate of E. rostratum was compared with two plant pathogenic isolates of E. rostratum and an isolate of the closely related genus Bipolaris in terms of morphology, phylogeny, and pathogenicity on one C3 grass, Gulf annual rye grass (Lolium multiflorum), and two C4 grasses, Japanese stilt grass (Microstegium vimineum) and bahia grass (Paspalum notatum). Colony growth and color, as well as conidia shape and size were the same for the clinical and plant isolates of E. rostratum, while these characteristics differed slightly for the Bipolaris sp. isolate. The plant pathogenic and clinical isolates of E. rostratum were indistinguishable based on morphology and ITS and 28S rDNA sequence analysis. The clinical isolate was as pathogenic to all grass species tested as the plant pathogenic strains that were originally isolated from plant hosts. The clinical isolate induced more severe symptoms on stilt grass than on rye grass, while this was the reverse for the plant isolates of E. rostratum. The phylogenetic similarity between the clinical and plant-associated E. rostratum isolates and the ability of the clinical isolate to infect plants suggests that a plant pathogenic strain of E. rostratum contaminated the corticosteroid injection fluid and was able to cause systemic disease in the affected patient. This is the first proof that a clinical isolate of E. rostratum is also an effective plant pathogen.

Exserohilum rostratum: Characterization of a Cross-Kingdom Pathogen of Plants and Humans

PubMed Central

Sharma, Kalpana; Goss, Erica M.; Dickstein, Ellen R.; Smith, Matthew E.; Johnson, Judith A.; Southwick, Frederick S.; van Bruggen, Ariena H. C.

2014-01-01

Pathogen host shifts represent a major source of new infectious diseases. There are several examples of cross-genus host jumps that have caused catastrophic epidemics in animal and plant species worldwide. Cross-kingdom jumps are rare, and are often associated with nosocomial infections. Here we provide an example of human-mediated cross-kingdom jumping of Exserohilum rostratum isolated from a patient who had received a corticosteroid injection and died of fungal meningitis in a Florida hospital in 2012. The clinical isolate of E. rostratum was compared with two plant pathogenic isolates of E. rostratum and an isolate of the closely related genus Bipolaris in terms of morphology, phylogeny, and pathogenicity on one C3 grass, Gulf annual rye grass (Lolium multiflorum), and two C4 grasses, Japanese stilt grass (Microstegium vimineum) and bahia grass (Paspalum notatum). Colony growth and color, as well as conidia shape and size were the same for the clinical and plant isolates of E. rostratum, while these characteristics differed slightly for the Bipolaris sp. isolate. The plant pathogenic and clinical isolates of E. rostratum were indistinguishable based on morphology and ITS and 28S rDNA sequence analysis. The clinical isolate was as pathogenic to all grass species tested as the plant pathogenic strains that were originally isolated from plant hosts. The clinical isolate induced more severe symptoms on stilt grass than on rye grass, while this was the reverse for the plant isolates of E. rostratum. The phylogenetic similarity between the clinical and plant-associated E. rostratum isolates and the ability of the clinical isolate to infect plants suggests that a plant pathogenic strain of E. rostratum contaminated the corticosteroid injection fluid and was able to cause systemic disease in the affected patient. This is the first proof that a clinical isolate of E. rostratum is also an effective plant pathogen. PMID:25285444

The trans-kingdom identification of negative regulators of pathogen hypervirulence

PubMed Central

Brown, Neil A.; Urban, Martin; Hammond-Kosack, Kim E.

2015-01-01

Modern society and global ecosystems are increasingly under threat from pathogens, which cause a plethora of human, animal, invertebrate and plant diseases. Of increasing concern is the trans-kingdom tendency for increased pathogen virulence that is beginning to emerge in natural, clinical and agricultural settings. The study of pathogenicity has revealed multiple examples of convergently evolved virulence mechanisms. Originally described as rare, but increasingly common, are interactions where a single gene deletion in a pathogenic species causes hypervirulence. This review utilised the pathogen–host interaction database (www.PHI-base.org) to identify 112 hypervirulent mutations from 37 pathogen species, and subsequently interrogates the trans-kingdom, conserved, molecular, biochemical and cellular themes that cause hypervirulence. This study investigates 22 animal and 15 plant pathogens including 17 bacterial and 17 fungal species. Finally, the evolutionary significance and trans-kingdom requirement for negative regulators of hypervirulence and the implication of pathogen hypervirulence and emerging infectious diseases on society are discussed. PMID:26468211

Pathogenic and Nonpathogenic Lifestyles in Colletotrichum acutatum from Strawberry and Other Plants.

PubMed

Freeman, S; Horowitz, S; Sharon, A

2001-10-01

ABSTRACT Anthracnose is one of the major fungal diseases of strawberry occurring worldwide. In Israel, the disease is caused primarily by the species Colletotrichum acutatum. The pathogen causes black spot on fruit, root necrosis, and crown rot resulting in mortality of transplants in the field. The host range and specificity of C. acutatum from strawberry was examined on pepper, eggplant, tomato, bean, and strawberry under greenhouse conditions. The fungus was recovered from all plant species over a 3-month period but caused disease symptoms only on strawberry. Epiphytic and endophytic (colonization) fungal growth in the different plant species was confirmed by reisolation from leaf tissues and by polymerase chain reaction (PCR)-specific primer amplification. C. acutatum was also isolated from healthy looking, asymptomatic plants of the weed genera Vicia and Conyza. Isolates that were recovered from the weeds caused disease symptoms on strawberry and were positively identified as C. acutatum by PCR. The habitation of a large number of plant species, including weeds, by C. acutatum suggests that, although it causes disease only on strawberry and anemone in Israel, this fungus can persist on many other plant species. Therefore, plants that are not considered hosts of C. acutatum may serve as a potential inoculum source for strawberry infection and permit survival of the pathogen between seasons.

Demonstrating concepts of pathogenesis using effectors of Phytophthora infestans

USDA-ARS?s Scientific Manuscript database

Pathogenesis, or how pathogens cause disease, is an important concept in plant pathology. The study of pathogenesis in plant pathology has rapidly expanded and is now a significant portion of plant pathology research (especially research at the molecular level of host-pathogen interaction). With the...

Water relations in the interaction of foliar bacterial pathogens with plants.

PubMed

Beattie, Gwyn A

2011-01-01

This review examines the many ways in which water influences the relations between foliar bacterial pathogens and plants. As a limited resource in aerial plant tissues, water is subject to manipulation by both plants and pathogens. A model is emerging that suggests that plants actively promote localized desiccation at the infection site and thus restrict pathogen growth as one component of defense. Similarly, many foliar pathogens manipulate water relations as one component of pathogenesis. Nonvascular pathogens do this using effectors and other molecules to alter hormonal responses and enhance intercellular watersoaking, whereas vascular pathogens use many mechanisms to cause wilt. Because of water limitations on phyllosphere surfaces, bacterial colonists, including pathogens, benefit from the protective effects of cellular aggregation, synthesis of hygroscopic polymers, and uptake and production of osmoprotective compounds. Moreover, these bacteria employ tactics for scavenging and distributing water to overcome water-driven barriers to nutrient acquisition, movement, and signal exchange on plant surfaces. Copyright © 2011 by Annual Reviews. All rights reserved.

Evolution and genome architecture in fungal plant pathogens.

PubMed

Möller, Mareike; Stukenbrock, Eva H

2017-12-01

The fungal kingdom comprises some of the most devastating plant pathogens. Sequencing the genomes of fungal pathogens has shown a remarkable variability in genome size and architecture. Population genomic data enable us to understand the mechanisms and the history of changes in genome size and adaptive evolution in plant pathogens. Although transposable elements predominantly have negative effects on their host, fungal pathogens provide prominent examples of advantageous associations between rapidly evolving transposable elements and virulence genes that cause variation in virulence phenotypes. By providing homogeneous environments at large regional scales, managed ecosystems, such as modern agriculture, can be conducive for the rapid evolution and dispersal of pathogens. In this Review, we summarize key examples from fungal plant pathogen genomics and discuss evolutionary processes in pathogenic fungi in the context of molecular evolution, population genomics and agriculture.

Understanding yield loss and pathogen biology to improve disease management: Stagonospora nodorum blotch - a case study in wheat

USDA-ARS?s Scientific Manuscript database

The estimated potential yield losses caused by plant pathogens are up to 16% globally, and most research in plant pathology aims to reduce yield loss in crops directly or indirectly. Yield losses caused by a certain disease depend not only on disease severity, but also on weather factors, the pathog...

Convergent Evolution of Pathogen Effectors toward Reactive Oxygen Species Signaling Networks in Plants.

PubMed

Jwa, Nam-Soo; Hwang, Byung Kook

2017-01-01

Microbial pathogens have evolved protein effectors to promote virulence and cause disease in host plants. Pathogen effectors delivered into plant cells suppress plant immune responses and modulate host metabolism to support the infection processes of pathogens. Reactive oxygen species (ROS) act as cellular signaling molecules to trigger plant immune responses, such as pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity. In this review, we discuss recent insights into the molecular functions of pathogen effectors that target multiple steps in the ROS signaling pathway in plants. The perception of PAMPs by pattern recognition receptors leads to the rapid and strong production of ROS through activation of NADPH oxidase Respiratory Burst Oxidase Homologs (RBOHs) as well as peroxidases. Specific pathogen effectors directly or indirectly interact with plant nucleotide-binding leucine-rich repeat receptors to induce ROS production and the hypersensitive response in plant cells. By contrast, virulent pathogens possess effectors capable of suppressing plant ROS bursts in different ways during infection. PAMP-triggered ROS bursts are suppressed by pathogen effectors that target mitogen-activated protein kinase cascades. Moreover, pathogen effectors target vesicle trafficking or metabolic priming, leading to the suppression of ROS production. Secreted pathogen effectors block the metabolic coenzyme NADP-malic enzyme, inhibiting the transfer of electrons to the NADPH oxidases (RBOHs) responsible for ROS generation. Collectively, pathogen effectors may have evolved to converge on a common host protein network to suppress the common plant immune system, including the ROS burst and cell death response in plants.

Conservation of Erwinia amylovora pathogenicity-relevant genes among Erwinia genomes.

PubMed

Borruso, Luigimaria; Salomone-Stagni, Marco; Polsinelli, Ivan; Schmitt, Armin Otto; Benini, Stefano

2017-12-01

The Erwinia genus comprises species that are plant pathogens, non-pathogen, epiphytes, and opportunistic human pathogens. Within the genus, Erwinia amylovora ranks among the top 10 plant pathogenic bacteria. It causes the fire blight disease and is a global threat to commercial apple and pear production. We analyzed the presence/absence of the E. amylovora genes reported to be important for pathogenicity towards Rosaceae within various Erwinia strains genomes. This simple bottom-up approach, allowed us to correlate the analyzed genes to pathogenicity, host specificity, and make useful considerations to drive targeted studies.

Emerging Trends in Molecular Interactions between Plants and the Broad Host Range Fungal Pathogens Botrytis cinerea and Sclerotinia sclerotiorum

PubMed Central

Mbengue, Malick; Navaud, Olivier; Peyraud, Rémi; Barascud, Marielle; Badet, Thomas; Vincent, Rémy; Barbacci, Adelin; Raffaele, Sylvain

2016-01-01

Fungal plant pathogens are major threats to food security worldwide. Sclerotinia sclerotiorum and Botrytis cinerea are closely related Ascomycete plant pathogens causing mold diseases on hundreds of plant species. There is no genetic source of complete plant resistance to these broad host range pathogens known to date. Instead, natural plant populations show a continuum of resistance levels controlled by multiple genes, a phenotype designated as quantitative disease resistance. Little is known about the molecular mechanisms controlling the interaction between plants and S. sclerotiorum and B. cinerea but significant advances were made on this topic in the last years. This minireview highlights a selection of nine themes that emerged in recent research reports on the molecular bases of plant-S. sclerotiorum and plant-B. cinerea interactions. On the fungal side, this includes progress on understanding the role of oxalic acid, on the study of fungal small secreted proteins. Next, we discuss the exchanges of small RNA between organisms and the control of cell death in plant and fungi during pathogenic interactions. Finally on the plant side, we highlight defense priming by mechanical signals, the characterization of plant Receptor-like proteins and the hormone abscisic acid in the response to B. cinerea and S. sclerotiorum, the role of plant general transcription machinery and plant small bioactive peptides. These represent nine trends we selected as remarkable in our understanding of fungal molecules causing disease and plant mechanisms associated with disease resistance to two devastating broad host range fungi. PMID:27066056

Antibacterial activity of caffeine against plant pathogenic bacteria.

PubMed

Sledz, Wojciech; Los, Emilia; Paczek, Agnieszka; Rischka, Jacek; Motyka, Agata; Zoledowska, Sabina; Piosik, Jacek; Lojkowska, Ewa

2015-01-01

The objective of the present study was to evaluate the antibacterial properties of a plant secondary metabolite - caffeine. Caffeine is present in over 100 plant species. Antibacterial activity of caffeine was examined against the following plant-pathogenic bacteria: Ralstonia solanacearum (Rsol), Clavibacter michiganesis subsp. sepedonicus (Cms), Dickeya solani (Dsol), Pectobacterium atrosepticum (Pba), Pectobacterium carotovorum subsp. carotovorum (Pcc), Pseudomonas syringae pv. tomato (Pst), and Xanthomonas campestris subsp. campestris (Xcc). MIC and MBC values ranged from 5 to 20 mM and from 43 to 100 mM, respectively. Caffeine increased the bacterial generation time of all tested species and caused changes in cell morphology. The influence of caffeine on the synthesis of DNA, RNA and proteins was investigated in cultures of plant pathogenic bacteria with labelled precursors: [(3)H]thymidine, [(3)H]uridine or (14)C leucine, respectively. RNA biosynthesis was more affected than DNA or protein biosynthesis in bacterial cells treated with caffeine. Treatment of Pba with caffeine for 336 h did not induce resistance to this compound. Caffeine application reduced disease symptoms caused by Dsol on chicory leaves, potato slices, and whole potato tubers. The data presented indicate caffeine as a potential tool for the control of diseases caused by plant-pathogenic bacteria, especially under storage conditions.

Convergent Evolution of Pathogen Effectors toward Reactive Oxygen Species Signaling Networks in Plants

PubMed Central

Jwa, Nam-Soo; Hwang, Byung Kook

2017-01-01

Microbial pathogens have evolved protein effectors to promote virulence and cause disease in host plants. Pathogen effectors delivered into plant cells suppress plant immune responses and modulate host metabolism to support the infection processes of pathogens. Reactive oxygen species (ROS) act as cellular signaling molecules to trigger plant immune responses, such as pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity. In this review, we discuss recent insights into the molecular functions of pathogen effectors that target multiple steps in the ROS signaling pathway in plants. The perception of PAMPs by pattern recognition receptors leads to the rapid and strong production of ROS through activation of NADPH oxidase Respiratory Burst Oxidase Homologs (RBOHs) as well as peroxidases. Specific pathogen effectors directly or indirectly interact with plant nucleotide-binding leucine-rich repeat receptors to induce ROS production and the hypersensitive response in plant cells. By contrast, virulent pathogens possess effectors capable of suppressing plant ROS bursts in different ways during infection. PAMP-triggered ROS bursts are suppressed by pathogen effectors that target mitogen-activated protein kinase cascades. Moreover, pathogen effectors target vesicle trafficking or metabolic priming, leading to the suppression of ROS production. Secreted pathogen effectors block the metabolic coenzyme NADP-malic enzyme, inhibiting the transfer of electrons to the NADPH oxidases (RBOHs) responsible for ROS generation. Collectively, pathogen effectors may have evolved to converge on a common host protein network to suppress the common plant immune system, including the ROS burst and cell death response in plants. PMID:29033963

Disease induction by human microbial pathogens in plant-model systems: potential, problems and prospects.

PubMed

van Baarlen, Peter; van Belkum, Alex; Thomma, Bart P H J

2007-02-01

Relatively simple eukaryotic model organisms such as the genetic model weed plant Arabidopsis thaliana possess an innate immune system that shares important similarities with its mammalian counterpart. In fact, some human pathogens infect Arabidopsis and cause overt disease with human symptomology. In such cases, decisive elements of the plant's immune system are likely to be targeted by the same microbial factors that are necessary for causing disease in humans. These similarities can be exploited to identify elementary microbial pathogenicity factors and their corresponding targets in a green host. This circumvents important cost aspects that often frustrate studies in humans or animal models and, in addition, results in facile ethical clearance.

Plant Pathogen-Induced Water-Soaking Promotes Salmonella enterica Growth on Tomato Leaves

PubMed Central

Potnis, Neha; Colee, James; Jones, Jeffrey B.

2015-01-01

Plant pathogen infection is a critical factor for the persistence of Salmonella enterica on plants. We investigated the mechanisms responsible for the persistence of S. enterica on diseased tomato plants by using four diverse bacterial spot Xanthomonas species that differ in disease severities. Xanthomonas euvesicatoria and X. gardneri infection fostered S. enterica growth, while X. perforans infection did not induce growth but supported the persistence of S. enterica. X. vesicatoria-infected leaves harbored S. enterica populations similar to those on healthy leaves. Growth of S. enterica was associated with extensive water-soaking and necrosis in X. euvesicatoria- and X. gardneri-infected plants. The contribution of water-soaking to the growth of S. enterica was corroborated by an increased growth of populations on water-saturated leaves in the absence of a plant pathogen. S. enterica aggregates were observed with bacterial spot lesions caused by either X. euvesicatoria or X. vesicatoria; however, more S. enterica aggregates formed on X. euvesicatoria-infected leaves as a result of larger lesion sizes per leaf area and extensive water-soaking. Sparsely distributed lesions caused by X. vesicatoria infection do not support the overall growth of S. enterica or aggregates in areas without lesions or water-soaking; S. enterica was observed as single cells and not aggregates. Thus, pathogen-induced water-soaking and necrosis allow S. enterica to replicate and proliferate on tomato leaves. The finding that the pathogen-induced virulence phenotype affects the fate of S. enterica populations in diseased plants suggests that targeting of plant pathogen disease is important in controlling S. enterica populations on plants. PMID:26386057

Machine learning for characterization of insect vector feeding

USDA-ARS?s Scientific Manuscript database

Insects that feed by ingesting plant and animal fluids cause devastating damage to humans, livestock, and agriculture worldwide, primarily by transmitting pathogens of plants and animals. The feeding processes required for successful pathogen transmission by sucking insects can be recorded by monito...

The role of effectors of biotrophic and hemibiotrophic fungi in infection.

PubMed

Koeck, Markus; Hardham, Adrienne R; Dodds, Peter N

2011-12-01

Biotrophic and hemibiotrophic fungi are successful groups of plant pathogens that require living plant tissue to survive and complete their life cycle. Members of these groups include the rust fungi and powdery mildews and species in the Ustilago, Cladosporium and Magnaporthe genera. Collectively, they represent some of the most destructive plant parasites, causing huge economic losses and threatening global food security. During plant infection, pathogens synthesize and secrete effector proteins, some of which are translocated into the plant cytosol where they can alter the host's response to the invading pathogen. In a successful infection, pathogen effectors facilitate suppression of the plant's immune system and orchestrate the reprogramming of the infected tissue so that it becomes a source of nutrients that are required by the pathogen to support its growth and development. This review summarizes our current understanding of the function of fungal effectors in infection. © 2011 Blackwell Publishing Ltd.

Duckweed (Lemna minor) as a model plant system for the study of human microbial pathogenesis.

PubMed

Zhang, Yong; Hu, Yangbo; Yang, Baoyu; Ma, Fang; Lu, Pei; Li, Lamei; Wan, Chengsong; Rayner, Simon; Chen, Shiyun

2010-10-25

Plant infection models provide certain advantages over animal models in the study of pathogenesis. However, current plant models face some limitations, e.g., plant and pathogen cannot co-culture in a contained environment. Development of such a plant model is needed to better illustrate host-pathogen interactions. We describe a novel model plant system for the study of human pathogenic bacterial infection on a large scale. This system was initiated by co-cultivation of axenic duckweed (Lemna minor) plants with pathogenic bacteria in 24-well polystyrene cell culture plate. Pathogenesis of bacteria to duckweed was demonstrated with Pseudomonas aeruginosa and Staphylococcus aureus as two model pathogens. P. aeruginosa PAO1 caused severe detriment to duckweed as judged from inhibition to frond multiplication and chlorophyll formation. Using a GFP-marked PAO1 strain, we demonstrated that bacteria colonized on both fronds and roots and formed biofilms. Virulence of PAO1 to duckweed was attenuated in its quorum sensing (QS) mutants and in recombinant strains overexpressing the QS quenching enzymes. RN4220, a virulent strain of S. aureus, caused severe toxicity to duckweed while an avirulent strain showed little effect. Using this system for antimicrobial chemical selection, green tea polyphenols exhibited inhibitory activity against S. aureus virulence. This system was further confirmed to be effective as a pathogenesis model using a number of pathogenic bacterial species. Our results demonstrate that duckweed can be used as a fast, inexpensive and reproducible model plant system for the study of host-pathogen interactions, could serve as an alternative choice for the study of some virulence factors, and could also potentially be used in large-scale screening for the discovery of antimicrobial chemicals.

Duckweed (Lemna minor) as a Model Plant System for the Study of Human Microbial Pathogenesis

PubMed Central

Zhang, Yong; Hu, Yangbo; Yang, Baoyu; Ma, Fang; Lu, Pei; Li, Lamei; Wan, Chengsong; Rayner, Simon; Chen, Shiyun

2010-01-01

Background Plant infection models provide certain advantages over animal models in the study of pathogenesis. However, current plant models face some limitations, e.g., plant and pathogen cannot co-culture in a contained environment. Development of such a plant model is needed to better illustrate host-pathogen interactions. Methodology/Principal Findings We describe a novel model plant system for the study of human pathogenic bacterial infection on a large scale. This system was initiated by co-cultivation of axenic duckweed (Lemna minor) plants with pathogenic bacteria in 24-well polystyrene cell culture plate. Pathogenesis of bacteria to duckweed was demonstrated with Pseudomonas aeruginosa and Staphylococcus aureus as two model pathogens. P. aeruginosa PAO1 caused severe detriment to duckweed as judged from inhibition to frond multiplication and chlorophyll formation. Using a GFP-marked PAO1 strain, we demonstrated that bacteria colonized on both fronds and roots and formed biofilms. Virulence of PAO1 to duckweed was attenuated in its quorum sensing (QS) mutants and in recombinant strains overexpressing the QS quenching enzymes. RN4220, a virulent strain of S. aureus, caused severe toxicity to duckweed while an avirulent strain showed little effect. Using this system for antimicrobial chemical selection, green tea polyphenols exhibited inhibitory activity against S. aureus virulence. This system was further confirmed to be effective as a pathogenesis model using a number of pathogenic bacterial species. Conclusions/Significance Our results demonstrate that duckweed can be used as a fast, inexpensive and reproducible model plant system for the study of host-pathogen interactions, could serve as an alternative choice for the study of some virulence factors, and could also potentially be used in large-scale screening for the discovery of antimicrobial chemicals. PMID:21049039

Fusarium species as pathogen on orchids.

PubMed

Srivastava, Shikha; Kadooka, Chris; Uchida, Janice Y

2018-03-01

The recent surge in demand for exotic ornamental crops such as orchids has led to a rise in international production, and a sharp increase in the number of plant and plant products moving between countries. Along with the plants, diseases are also being transported and introduced into new areas. Fusarium is one of the major diseases causing pathogens infecting orchids that is spreading through international trade. Studies have identified several species of Fusarium associated with orchids, some are pathogenic and cause symptoms such as leaf and flower spots, leaf or sheath blights, pseudostem or root rots, and wilts. Infection and damage caused by Fusarium reduces the quality of plants and flowers, and can cause severe economic losses. This review documents the current status of the Fusarium-orchid interaction, and illustrates challenges and future perspectives based on the available literature. This review is the first of Fusarium and orchid interactions, and integrates diverse results that both furthers the understanding and knowledge of this disease complex, and will enable the development of effective disease management practices. Copyright © 2017 Elsevier GmbH. All rights reserved.

Plant innate immunity: an updated insight into defense mechanism.

PubMed

Muthamilarasan, Mehanathan; Prasad, Manoj

2013-06-01

Plants are invaded by an array of pathogens of which only a few succeed in causing disease. The attack by others is countered by a sophisticated immune system possessed by the plants. The plant immune system is broadly divided into two, viz. microbial-associated molecular-patterns-triggered immunity (MTI) and effector-triggered immunity (ETI). MTI confers basal resistance, while ETI confers durable resistance, often resulting in hypersensitive response. Plants also possess systemic acquired resistance (SAR), which provides long-term defense against a broad-spectrum of pathogens. Salicylic-acid-mediated systemic acquired immunity provokes the defense response throughout the plant system during pathogen infection at a particular site. Trans-generational immune priming allows the plant to heritably shield their progeny towards pathogens previously encountered. Plants circumvent the viral infection through RNA interference phenomena by utilizing small RNAs. This review summarizes the molecular mechanisms of plant immune system, and the latest breakthroughs reported in plant defense. We discuss the plant–pathogen interactions and integrated defense responses in the context of presenting an integral understanding in plant molecular immunity.

The early response during the interaction of fungal phytopathogen and host plant.

PubMed

Shen, Yilin; Liu, Na; Li, Chuang; Wang, Xin; Xu, Xiaomeng; Chen, Wan; Xing, Guozhen; Zheng, Wenming

2017-05-01

Plants can be infected by a variety of pathogens, most of which can cause severe economic losses. The plants resist the invasion of pathogens via the innate or acquired immune system for surviving biotic stress. The associations between plants and pathogens are sophisticated beyond imaging and the interactions between them can occur at a very early stage after their touching each other. A number of researchers in the past decade have shown that many biochemical events appeared even as early as 5 min after their touching for plant disease resistance response. The early molecular interactions of plants and pathogens are likely to involve protein phosphorylation, ion fluxes, reactive oxygen species (ROS) and other signalling transduction. Here, we reviewed the recent progress in the study for molecular interaction response of fungal pathogens and host plant at the early infection stage, which included many economically important crop fungal pathogens such as cereal rust fungi, tomato Cladosporium fulvum , rice blast and so on. By dissecting the earlier infection stage of the diseases, the avirulent/virulent genes of pathogen or resistance genes of plant could be defined more clearly and accurately, which would undoubtedly facilitate fungal pathogenesis study and resistant crop breeding. © 2017 The Authors.

The early response during the interaction of fungal phytopathogen and host plant

PubMed Central

Shen, Yilin; Liu, Na; Li, Chuang; Wang, Xin; Xu, Xiaomeng; Chen, Wan; Xing, Guozhen

2017-01-01

Plants can be infected by a variety of pathogens, most of which can cause severe economic losses. The plants resist the invasion of pathogens via the innate or acquired immune system for surviving biotic stress. The associations between plants and pathogens are sophisticated beyond imaging and the interactions between them can occur at a very early stage after their touching each other. A number of researchers in the past decade have shown that many biochemical events appeared even as early as 5 min after their touching for plant disease resistance response. The early molecular interactions of plants and pathogens are likely to involve protein phosphorylation, ion fluxes, reactive oxygen species (ROS) and other signalling transduction. Here, we reviewed the recent progress in the study for molecular interaction response of fungal pathogens and host plant at the early infection stage, which included many economically important crop fungal pathogens such as cereal rust fungi, tomato Cladosporium fulvum, rice blast and so on. By dissecting the earlier infection stage of the diseases, the avirulent/virulent genes of pathogen or resistance genes of plant could be defined more clearly and accurately, which would undoubtedly facilitate fungal pathogenesis study and resistant crop breeding. PMID:28469008

Pathogen Phytosensing: Plants to Report Plant Pathogens.

PubMed

Mazarei, Mitra; Teplova, Irina; Hajimorad, M Reza; Stewart, C Neal

2008-04-14

Real-time systems that provide evidence of pathogen contamination in crops can be an important new line of early defense in agricultural centers. Plants possess defense mechanisms to protect against pathogen attack. Inducible plant defense is controlled by signal transduction pathways, inducible promoters and cis-regulatory elements corresponding to key genes involved in defense, and pathogen-specific responses. Identified inducible promoters and cis-acting elements could be utilized in plant sentinels, or 'phytosensors', by fusing these to reporter genes to produce plants with altered phenotypes in response to the presence of pathogens. Here, we have employed cis-acting elements from promoter regions of pathogen inducible genes as well as those responsive to the plant defense signal molecules salicylic acid, jasmonic acid, and ethylene. Synthetic promoters were constructed by combining various regulatory elements supplemented with the enhancer elements from the Cauliflower mosaic virus (CaMV) 35S promoter to increase basal level of the GUS expression. The inducibility of each synthetic promoter was first assessed in transient expression assays using Arabidopsis thaliana protoplasts and then examined for efficacy in stably transgenic Arabidopsis and tobacco plants. Histochemical and fluorometric GUS expression analyses showed that both transgenic Arabidopsis and tobacco plants responded to elicitor and phytohormone treatments with increased GUS expression when compared to untreated plants. Pathogen-inducible phytosensor studies were initiated by analyzing the sensitivity of the synthetic promoters against virus infection. Transgenic tobacco plants infected with Alfalfa mosaic virus showed an increase in GUS expression when compared to mock-inoculated control plants, whereas Tobacco mosaic virus infection caused no changes in GUS expression. Further research, using these transgenic plants against a range of different pathogens with the regulation of detectable reporter gene could provide biological evidence to define the functional differences between pathogens, and provide new technology and applications for transgenic plants as phytosensors.

Comparative genomic analyses of Clavibacter michiganensis subsp. insidiosus and aggressiveness on Medicago truncatula

USDA-ARS?s Scientific Manuscript database

Clavibacter michiganensis is the most economically important gram-positive bacterial plant pathogen with subspecies that cause serious diseases of maize, wheat, tomato, potato, and alfalfa. Much less is known about pathogenesis involving gram-positive plant pathogens than is known for gram-negative ...

Mechanisms of nuclear suppression of host immunity by effectors from the Arabidopsis downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa).

PubMed

Caillaud, M-C; Wirthmueller, L; Fabro, G; Piquerez, S J M; Asai, S; Ishaque, N; Jones, J D G

2012-01-01

Filamentous phytopathogens form sophisticated intracellular feeding structures called haustoria in plant cells. Pathogen effectors are likely to play a role in the establishment and maintenance of haustoria additional to their more characterized role of suppressing plant defense. Recent studies suggest that effectors may manipulate host transcription or other nuclear regulatory components for the benefit of pathogen development. However, the specific mechanisms by which these effectors promote susceptibility remain unclear. Of two recent screenings, we identified 15 nuclear-localized Hpa effectors (HaRxLs) that interact directly or indirectly with host nuclear components. When stably expressed in planta, nuclear HaRxLs cause diverse developmental phenotypes highlighting that nuclear effectors might interfere with fundamental plant regulatory mechanisms. Here, we report recent advances in understanding how a pathogen can manipulate nuclear processes in order to cause disease.

Machine Learning for Characterization of Insect Vector Feeding

PubMed Central

Willett, Nora S.; Stelinski, Lukasz L.; Lapointe, Stephen L.

2016-01-01

Insects that feed by ingesting plant and animal fluids cause devastating damage to humans, livestock, and agriculture worldwide, primarily by transmitting pathogens of plants and animals. The feeding processes required for successful pathogen transmission by sucking insects can be recorded by monitoring voltage changes across an insect-food source feeding circuit. The output from such monitoring has traditionally been examined manually, a slow and onerous process. We taught a computer program to automatically classify previously described insect feeding patterns involved in transmission of the pathogen causing citrus greening disease. We also show how such analysis contributes to discovery of previously unrecognized feeding states and can be used to characterize plant resistance mechanisms. This advance greatly reduces the time and effort required to analyze insect feeding, and should facilitate developing, screening, and testing of novel intervention strategies to disrupt pathogen transmission affecting agriculture, livestock and human health. PMID:27832081

Dermatosis due to plants (phytodermatosis).

PubMed

dos Reis, Vitor Manoel Silva

2010-01-01

Dermatosis caused by plants is relatively common and may occur by various pathogenic mechanisms. Dermatitis due to physical trauma, pharmacological action, irritation, sensitization, mediated by IgE and induced by light are described. Pseudophytodermatosis caused by plant-delivered elements is also described in the introduction to this work.

Defense-related proteins involved in sugarcane responses to biotic stress

PubMed Central

Souza, Thais P.; Dias, Renata O.; Silva-Filho, Marcio C.

2017-01-01

Abstract Sugarcane is one of the most important agricultural crops in the world. However, pathogen infection and herbivore attack cause constant losses in yield. Plants respond to pathogen infection by inducing the expression of several protein types, such as glucanases, chitinases, thaumatins, peptidase inhibitors, defensins, catalases and glycoproteins. Proteins induced by pathogenesis are directly or indirectly involved in plant defense, leading to pathogen death or inducing other plant defense responses. Several of these proteins are induced in sugarcane by different pathogens or insects and have antifungal or insecticidal activity. In this review, defense-related proteins in sugarcane are described, with their putative mechanisms of action, pathogen targets and biotechnological perspectives. PMID:28222203

Complete Genome Sequence of Pseudomonas fluorescens LBUM636, a Strain with Biocontrol Capabilities against Late Blight of Potato

PubMed Central

Morrison, Christopher K.; Novinscak, Amy; Gadkar, Vijay J.; Joly, David L.

2016-01-01

Herein provided is the full-genome sequence of Pseudomonas fluorescens LBUM636. This strain is a plant growth-promoting rhizobacterium (PGPR) which produces phenazine-1-carboxylic acid, an antibiotic involved in the biocontrol of numerous plant pathogens, including late blight of potato caused by the plant pathogen Phytophthora infestans. PMID:27231373

Plant pathogen-induced water-soaking promotes Salmonella enterica growth on tomato leaves.

PubMed

Potnis, Neha; Colee, James; Jones, Jeffrey B; Barak, Jeri D

2015-12-01

Plant pathogen infection is a critical factor for the persistence of Salmonella enterica on plants. We investigated the mechanisms responsible for the persistence of S. enterica on diseased tomato plants by using four diverse bacterial spot Xanthomonas species that differ in disease severities. Xanthomonas euvesicatoria and X. gardneri infection fostered S. enterica growth, while X. perforans infection did not induce growth but supported the persistence of S. enterica. X. vesicatoria-infected leaves harbored S. enterica populations similar to those on healthy leaves. Growth of S. enterica was associated with extensive water-soaking and necrosis in X. euvesicatoria- and X. gardneri-infected plants. The contribution of water-soaking to the growth of S. enterica was corroborated by an increased growth of populations on water-saturated leaves in the absence of a plant pathogen. S. enterica aggregates were observed with bacterial spot lesions caused by either X. euvesicatoria or X. vesicatoria; however, more S. enterica aggregates formed on X. euvesicatoria-infected leaves as a result of larger lesion sizes per leaf area and extensive water-soaking. Sparsely distributed lesions caused by X. vesicatoria infection do not support the overall growth of S. enterica or aggregates in areas without lesions or water-soaking; S. enterica was observed as single cells and not aggregates. Thus, pathogen-induced water-soaking and necrosis allow S. enterica to replicate and proliferate on tomato leaves. The finding that the pathogen-induced virulence phenotype affects the fate of S. enterica populations in diseased plants suggests that targeting of plant pathogen disease is important in controlling S. enterica populations on plants. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

Novel methods for pathogen control in livestock preharvest: An update

USDA-ARS?s Scientific Manuscript database

Pathogenic bacteria are found asymptomatically within and on food animals, which often results in pathogen entry into the food chain, causing human illnesses. Slaughter and processing plants do an outstanding job in reducing pathogen contamination through the use of intervention strategies after sl...

Evaluating host resistance to Macrophomina crown rot in strawberry

USDA-ARS?s Scientific Manuscript database

Macrophomina crown rot, caused by the soilborne fungus Macrophomina phaseolina, is an emerging pathogen in California strawberry production. When established, the pathogen can cause extensive plant decline and mortality. Host resistance will be a critical tool for managing this disease and guiding ...

Molecular characterization of pathogenic Fusarium species in cucurbit plants from Kermanshah province, Iran

PubMed Central

Chehri, K.; Salleh, B.; Yli-Mattila, T.; Reddy, K.R.N.; Abbasi, S.

2011-01-01

Fusarium is one of the important phytopathogenic genera of microfungi causing serious losses on cucurbit plants in Kermanshah province, the largest area of cucurbits plantation in Iran. Therefore, the objectives in this study were to isolate and identify disease-causing Fusarium spp. from infected cucurbit plants, to ascertain their pathogenicity, and to determine their phylogenetic relationships. A total of 100 Fusarium isolates were obtained from diseased cucurbit plants collected from fields in different geographic regions in Kermanshah province, Iran. According to morphological characters, all isolates were identified as Fusarium oxysporum, Fusarium proliferatum, Fusarium equiseti, Fusarium semitectum and Fusarium solani. All isolates of the five Fusarium spp. were evaluated for their pathogenicity on healthy cucumber (Cucumis sativus) and honeydew melon (Cucumis melo) seedlings in the glasshouse. F. oxysporum caused damping-off in 20–35 days on both cucurbit seedlings tested. Typical stem rot symptoms were observed within 15 days after inoculation with F. solani on both seedlings. Based on the internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA) restriction fragment length polymorphism (RFLP) analysis, the five Fusarium species were divided into two major groups. In particular, isolates belonging to the F. solani species complex (FSSC) were separated into two RFLP types. Grouping among Fusarium strains derived from restriction analysis was in agreement with criteria used in morphological classification. Therefore, the PCR-ITS-RFLP method provides a simple and rapid procedure for the differentiation of Fusarium strains at species level. This is the first report on identification and pathogenicity of major plant pathogenic Fusarium spp. causing root and stem rot on cucurbits in Iran. PMID:23961146

Studying plant-pathogen interactions in the genomics era: beyond molecular Koch’s postulates to systems biology

USDA-ARS?s Scientific Manuscript database

Molecular factors enabling microbial pathogens to cause plant diseases have been sought with increasing efficacy over three research eras, which successively introduced the tools of disease physiology, single-gene molecular genetics, and genomics. From this work emerged a unified model of the intera...

A Review of the Interactions between Wheat and Wheat Pathogens: Zymoseptoria tritici, Fusarium spp. and Parastagonospora nodorum

PubMed Central

Duba, Adrian; Goriewa-Duba, Klaudia; Wachowska, Urszula

2018-01-01

Zymoseptoria tritici is a hemibiotrophic pathogen which causes Septoria leaf blotch in wheat. The pathogenesis of the disease consists of a biotrophic phase and a necrotrophic phase. The pathogen infects the host plant by suppressing its immune response in the first stage of infection. Hemibiotrophic pathogens of the genus Fusarium cause Fusarium head blight, and the necrotrophic Parastagonospora nodorum is responsible for Septoria nodorum blotch in wheat. Cell wall-degrading enzymes in plants promote infections by necrotrophic and hemibiotrophic pathogens, and trichothecenes, secondary fungal metabolites, facilitate infections caused by fungi of the genus Fusarium. There are no sources of complete resistance to the above pathogens in wheat. Defense mechanisms in wheat are controlled by many genes encoding resistance traits. In the wheat genome, the characteristic features of loci responsible for resistance to pathogenic infections indicate that at least several dozen genes encode resistance to pathogens. The molecular interactions between wheat and Z. tritici, P. nodorum and Fusarium spp. pathogens have been insufficiently investigated. Most studies focus on the mechanisms by which the hemibiotrophic Z. tritici suppresses immune responses in plants and the role of mycotoxins and effector proteins in infections caused by P. nodorum and Fusarium spp. fungi. Trichothecene glycosylation and effector proteins, which are involved in defense responses in wheat, have been described at the molecular level. Recent advances in molecular biology have produced interesting findings which should be further elucidated in studies of molecular interactions between wheat and fungal pathogens. The Clustered Regularly-Interspaced Short Palindromic Repeats/ CRISPR associated (CRISPR/Cas) system can be used to introduce targeted mutations into the wheat genome and confer resistance to selected fungal diseases. Host-induced gene silencing and spray-induced gene silencing are also useful tools for analyzing wheat–pathogens interactions which can be used to develop new strategies for controlling fungal diseases. PMID:29642627

Lost in diversity: the interactions between soil-borne fungi, biodiversity and plant productivity.

PubMed

Mommer, Liesje; Cotton, T E Anne; Raaijmakers, Jos M; Termorshuizen, Aad J; van Ruijven, Jasper; Hendriks, Marloes; van Rijssel, Sophia Q; van de Mortel, Judith E; van der Paauw, Jan Willem; Schijlen, Elio G W M; Smit-Tiekstra, Annemiek E; Berendse, Frank; de Kroon, Hans; Dumbrell, Alex J

2018-04-01

There is consensus that plant species richness enhances plant productivity within natural grasslands, but the underlying drivers remain debated. Recently, differential accumulation of soil-borne fungal pathogens across the plant diversity gradient has been proposed as a cause of this pattern. However, the below-ground environment has generally been treated as a 'black box' in biodiversity experiments, leaving these fungi unidentified. Using next generation sequencing and pathogenicity assays, we analysed the community composition of root-associated fungi from a biodiversity experiment to examine if evidence exists for host specificity and negative density dependence in the interplay between soil-borne fungi, plant diversity and productivity. Plant species were colonised by distinct (pathogenic) fungal communities and isolated fungal species showed negative, species-specific effects on plant growth. Moreover, 57% of the pathogenic fungal operational taxonomic units (OTUs) recorded in plant monocultures were not detected in eight plant species plots, suggesting a loss of pathogenic OTUs with plant diversity. Our work provides strong evidence for host specificity and negative density-dependent effects of root-associated fungi on plant species in grasslands. Our work substantiates the hypothesis that fungal root pathogens are an important driver of biodiversity-ecosystem functioning relationships. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

Use of Endophytic and Rhizosphere Actinobacteria from Grapevine Plants To Reduce Nursery Fungal Graft Infections That Lead to Young Grapevine Decline

PubMed Central

Álvarez-Pérez, José Manuel; González-García, Sandra; Cobos, Rebeca; Olego, Miguel Ángel; Ibañez, Ana; Díez-Galán, Alba; Garzón-Jimeno, Enrique

2017-01-01

ABSTRACT Endophytic and rhizosphere actinobacteria isolated from the root system of 1-year-old grafted Vitis vinifera plants were evaluated for their activities against fungi that cause grapevine trunk diseases. A total of 58 endophytic and 94 rhizosphere isolates were tested. Based on an in vitro bioassay, 15.5% of the endophytic isolates and 30.8% of the rhizosphere isolates exhibited antifungal activity against the fungal pathogen Diplodia seriata, whereas 13.8% of the endophytic isolates and 16.0% of the rhizosphere isolates showed antifungal activity against Dactylonectria macrodidyma (formerly Ilyonectria macrodidyma). The strains which showed the greatest in vitro efficacy against both pathogens were further analyzed for their ability to inhibit the growth of Phaeomoniella chlamydospora and Phaeoacremonium minimum (formerly Phaeoacremonium aleophilum). Based on their antifungal activity, three rhizosphere isolates and three endophytic isolates were applied on grafts in an open-root field nursery in a 3-year trial. The field trial led to the identification of one endophytic strain, Streptomyces sp. VV/E1, and two rhizosphere isolates, Streptomyces sp. VV/R1 and Streptomyces sp. VV/R4, which significantly reduced the infection rates produced by the fungal pathogens Dactylonectria sp., Ilyonectria sp., P. chlamydospora, and P. minimum, all of which cause young grapevine decline. The VV/R1 and VV/R4 isolates also significantly reduced the mortality level of grafted plants in the nursery. This study shows that certain actinobacteria could represent a promising new tool for controlling fungal trunk pathogens that infect grapevine plants through the root system in nurseries. IMPORTANCE Grapevine trunk diseases are a major threat to the wine and grape industry worldwide. They cause a significant reduction in yields as well as in grape quality, and they can even cause plant death. Trunk diseases are caused by fungal pathogens that enter through pruning wounds and/or the root system. Although different strategies have recently been developed to protect pruning wounds using antifungal compounds (natural or synthetic) or biocontrol agents, no tools are yet available for controlling soil pathogens that infect plants through their root system. This study shows that different actinobacterial isolates, when applied to grafts in a nursery, can significantly reduce the infection rate caused by fungal pathogens that enter through the root system. This is a new, promising, and green alternative for preventing the decline of young grapevines in nurseries and vineyards. PMID:28986378

Use of Endophytic and Rhizosphere Actinobacteria from Grapevine Plants To Reduce Nursery Fungal Graft Infections That Lead to Young Grapevine Decline.

PubMed

Álvarez-Pérez, José Manuel; González-García, Sandra; Cobos, Rebeca; Olego, Miguel Ángel; Ibañez, Ana; Díez-Galán, Alba; Garzón-Jimeno, Enrique; Coque, Juan José R

2017-12-15

Endophytic and rhizosphere actinobacteria isolated from the root system of 1-year-old grafted Vitis vinifera plants were evaluated for their activities against fungi that cause grapevine trunk diseases. A total of 58 endophytic and 94 rhizosphere isolates were tested. Based on an in vitro bioassay, 15.5% of the endophytic isolates and 30.8% of the rhizosphere isolates exhibited antifungal activity against the fungal pathogen Diplodia seriata , whereas 13.8% of the endophytic isolates and 16.0% of the rhizosphere isolates showed antifungal activity against Dactylonectria macrodidyma (formerly Ilyonectria macrodidyma ). The strains which showed the greatest in vitro efficacy against both pathogens were further analyzed for their ability to inhibit the growth of Phaeomoniella chlamydospora and Phaeoacremonium minimum (formerly Phaeoacremonium aleophilum ). Based on their antifungal activity, three rhizosphere isolates and three endophytic isolates were applied on grafts in an open-root field nursery in a 3-year trial. The field trial led to the identification of one endophytic strain, Streptomyces sp. VV/E1, and two rhizosphere isolates, Streptomyces sp. VV/R1 and Streptomyces sp. VV/R4, which significantly reduced the infection rates produced by the fungal pathogens Dactylonectria sp., Ilyonectria sp., P. chlamydospora , and P. minimum , all of which cause young grapevine decline. The VV/R1 and VV/R4 isolates also significantly reduced the mortality level of grafted plants in the nursery. This study shows that certain actinobacteria could represent a promising new tool for controlling fungal trunk pathogens that infect grapevine plants through the root system in nurseries. IMPORTANCE Grapevine trunk diseases are a major threat to the wine and grape industry worldwide. They cause a significant reduction in yields as well as in grape quality, and they can even cause plant death. Trunk diseases are caused by fungal pathogens that enter through pruning wounds and/or the root system. Although different strategies have recently been developed to protect pruning wounds using antifungal compounds (natural or synthetic) or biocontrol agents, no tools are yet available for controlling soil pathogens that infect plants through their root system. This study shows that different actinobacterial isolates, when applied to grafts in a nursery, can significantly reduce the infection rate caused by fungal pathogens that enter through the root system. This is a new, promising, and green alternative for preventing the decline of young grapevines in nurseries and vineyards. Copyright © 2017 American Society for Microbiology.

Occurrence of Root Rot and Vascular Wilt Diseases in Roselle (Hibiscus sabdariffa L.) in Upper Egypt.

PubMed

Hassan, Naglaa; Shimizu, Masafumi; Hyakumachi, Mitsuro

2014-03-01

Roselle (Hibiscus sabdariffa L.) family Malvaceae is an important crop used in food, cosmetics and pharmaceutics industries. Roselle is cultivated mainly in Upper Egypt (Qena and Aswan governorates) producing 94% of total production. Root rot disease of roselle is one of the most important diseases that attack both seedlings and adult plants causing serious losses in crop productivity and quality. The main objective of the present study is to identify and characterize pathogens associated with root rot and wilt symptoms of roselle in Qena, Upper Egypt and evaluate their pathogenicity under greenhouse and field condition. Fusarium oxysporum, Macrophomina phaseolina, Fusarium solani, Fusarium equiseti and Fusarium semitectum were isolated from the natural root rot diseases in roselle. All isolated fungi were morphologically characterized and varied in their pathogenic potentialities. They could attack roselle plants causing damping-off and root rot/wilt diseases in different pathogenicity tests. The highest pathogenicity was caused by F. oxysporum and M. phaseolina followed by F. solani. The least pathogenic fungi were F. equiseti followed by F. semitectum. It obviously noted that Baladi roselle cultivar was more susceptible to infection with all tested fungi than Sobhia 17 under greenhouse and field conditions. This is the first report of fungal pathogens causing root rot and vascular wilt in roselle in Upper Egypt.

Temporal interactions of plant - insect - predator after infection of bacterial pathogen on rice plants.

PubMed

Sun, Ze; Liu, Zhuang; Zhou, Wen; Jin, Huanan; Liu, Hao; Zhou, Aiming; Zhang, Aijun; Wang, Man-Qun

2016-05-17

Pathogenic infection on plants may affect interactions of host-plants with their herbivores, as well as the herbivores with their predators. In this study, the effects of infection by pathogenic bacterium Xanthomonas oryzae pv. oryzae (Xoo), which causes a vascular disease in rice, on rice plants and consequent interactions with a rice herbivore, brown rice planthopper (BPH) Nilaparvata lugens, and its major predator, Cyrtorhinus lividipennis, were investigated. The results showed that the rice plants exhibited increased resistance to BPH only at 3 d post-inoculation of Xoo, while the Xoo infection did not affect the development and fecundity of BPH. BPH exhibited a higher preference to Xoo infected rice plants, whereas C. lividipennis preferred the Xoo infected rice plants after BPH fed, but preferred healthy rice plants without BPH fed. Volatile organic compounds emitted from Xoo rice were significantly higher than those from healthy rice plants, Xoo infection on BPH fed plants caused rice plants to emit more the herbivore-induced plant volatiles, while all of these changes correlated to the temporal dimension. These results demonstrated that Xoo infection significantly influenced the interactions of rice plants with two non-vectors, BPH and its predator, although these effects exhibited in a temporal pattern after infection.

The type III secreted effector DspE is required early in Solanum tuberosum leaf infection by Pectobacterium carotovorum to elicit cell death, and requires Wx(3-6)D/E motifs

USDA-ARS?s Scientific Manuscript database

Pectobacterium species are enterobacterial plant-pathogens that cause soft rot disease in diverse plant species. Unlike hemi-biotrophic plant pathogenic bacteria, the type III secretion system (T3SS) of Pectobacterium carotovorum subsp. carotovorum (P. carotovorum) appears to secrete only one effect...

Isolating Fungal Pathogens from a Dynamic Disease Outbreak in a Native Plant Population to Establish Plant-Pathogen Bioassays for the Ecological Model Plant Nicotiana attenuata

PubMed Central

Schuck, Stefan; Baldwin, Ian T.

2014-01-01

The wild tobacco species Nicotiana attenuata has been intensively used as a model plant to study its interaction with insect herbivores and pollinators in nature, however very little is known about its native pathogen community. We describe a fungal disease outbreak in a native N. attenuata population comprising 873 plants growing in an area of about 1500 m2. The population was divided into 14 subpopulations and disease symptom development in the subpopulations was monitored for 16 days, revealing a waxing and waning of visible disease symptoms with some diseased plants recovering fully. Native fungal N. attenuata pathogens were isolated from diseased plants, characterized genetically, chemotaxonomically and morphologically, revealing several isolates of the ascomycete genera Fusarium and Alternaria, that differed in the type and strength of the disease symptoms they caused in bioassays on either detached leaves or intact soil-grown plants. These isolates and the bioassays will empower the study of N. attenuata-pathogen interactions in a realistic ecological context. PMID:25036191

Combating Pathogenic Microorganisms Using Plant-Derived Antimicrobials: A Minireview of the Mechanistic Basis

PubMed Central

Upadhyaya, Indu; Kollanoor-Johny, Anup

2014-01-01

The emergence of antibiotic resistance in pathogenic bacteria has led to renewed interest in exploring the potential of plant-derived antimicrobials (PDAs) as an alternative therapeutic strategy to combat microbial infections. Historically, plant extracts have been used as a safe, effective, and natural remedy for ailments and diseases in traditional medicine. Extensive research in the last two decades has identified a plethora of PDAs with a wide spectrum of activity against a variety of fungal and bacterial pathogens causing infections in humans and animals. Active components of many plant extracts have been characterized and are commercially available; however, research delineating the mechanistic basis of their antimicrobial action is scanty. This review highlights the potential of various plant-derived compounds to control pathogenic bacteria, especially the diverse effects exerted by plant compounds on various virulence factors that are critical for pathogenicity inside the host. In addition, the potential effect of PDAs on gut microbiota is discussed. PMID:25298964

Fusarium-induced diseases of tropical, perennial crops.

PubMed

Ploetz, Randy C

2006-06-01

ABSTRACT The world's oldest ecosystems are found in the tropics. They are diverse, highly evolved, but barely understood. This and subsequent papers describe diseases of tropical, perennial plants that are caused by Fusarium spp. Many of these are economically significant, difficult to manage, and of scientific interest. Some represent coevolved patho-systems (e.g., Panama disease, tracheomycosis of coffee, fusariosis of pineapple, and Fusarium wilt of oil palm), whereas others may be new-encounter diseases or are caused by generalist pathogens (cushion gall of cacao). New vector relationships are evident in other pathosystems (e.g., mango malformation), and two or more pathogens have been shown to cause some of the diseases (Panama disease and tracheomycosis of coffee). More work on these pathosystems is warranted as they could reveal much about the evolution of plant pathogens and the important diseases they cause.

Long-distance endosome trafficking drives fungal effector production during plant infection

PubMed Central

Bielska, Ewa; Higuchi, Yujiro; Schuster, Martin; Steinberg, Natascha; Kilaru, Sreedhar; Talbot, Nicholas J.; Steinberg, Gero

2014-01-01

To cause plant disease, pathogenic fungi can secrete effector proteins into plant cells to suppress plant immunity and facilitate fungal infection. Most fungal pathogens infect plants using very long strand-like cells, called hyphae, that secrete effectors from their tips into host tissue. How fungi undergo long-distance cell signalling to regulate effector production during infection is not known. Here we show that long-distance retrograde motility of early endosomes (EEs) is necessary to trigger transcription of effector-encoding genes during plant infection by the pathogenic fungus Ustilago maydis. We demonstrate that motor-dependent retrograde EE motility is necessary for regulation of effector production and secretion during host cell invasion. We further show that retrograde signalling involves the mitogen-activated kinase Crk1 that travels on EEs and participates in control of effector production. Fungal pathogens therefore undergo long-range signalling to orchestrate host invasion. PMID:25283249

Long-distance endosome trafficking drives fungal effector production during plant infection.

PubMed

Bielska, Ewa; Higuchi, Yujiro; Schuster, Martin; Steinberg, Natascha; Kilaru, Sreedhar; Talbot, Nicholas J; Steinberg, Gero

2014-10-06

To cause plant disease, pathogenic fungi can secrete effector proteins into plant cells to suppress plant immunity and facilitate fungal infection. Most fungal pathogens infect plants using very long strand-like cells, called hyphae, that secrete effectors from their tips into host tissue. How fungi undergo long-distance cell signalling to regulate effector production during infection is not known. Here we show that long-distance retrograde motility of early endosomes (EEs) is necessary to trigger transcription of effector-encoding genes during plant infection by the pathogenic fungus Ustilago maydis. We demonstrate that motor-dependent retrograde EE motility is necessary for regulation of effector production and secretion during host cell invasion. We further show that retrograde signalling involves the mitogen-activated kinase Crk1 that travels on EEs and participates in control of effector production. Fungal pathogens therefore undergo long-range signalling to orchestrate host invasion.

Characterization of microsatellites in Fusicladium effusum, cause of pecan scab

USDA-ARS?s Scientific Manuscript database

Pecan scab, caused by the plant pathogenic fungus Fusicladium effusum, is the most destructive disease of pecan. Little is known of the population genetic diversity of this pathogen. In this study, microsatellites were mined from the F. effusum genome, and flanking primers were subsequently designed...

Gall-ID: Tools for genotyping gall-causing phytopathogenic bacteria

USDA-ARS?s Scientific Manuscript database

Understanding the population structure and genetic diversity of plant pathogens, as well as the effect of agricultural practices on pathogen evolution, are important for disease management. Developments in molecular methods have contributed to increasing the resolution for accurate pathogen identifi...

Draft genome sequence of ‘Candidatus Phytoplasma pruni’ strain CX, a plant pathogenic bacterium

USDA-ARS?s Scientific Manuscript database

‘Candidatus Phytoplasma pruni’ strain CX, belonging to subgroup 16SrIII-A, is a plant pathogenic bacterium causing economically important diseases in many fruit crops. Here we report the draft genome sequence that consists of 598,508 bases, with a G+C content of 27.21 mol%. ...

Pathogen Phytosensing: Plants to Report Plant Pathogens

PubMed Central

Mazarei, Mitra; Teplova, Irina; Hajimorad, M. Reza; Stewart, C. Neal

2008-01-01

Real-time systems that provide evidence of pathogen contamination in crops can be an important new line of early defense in agricultural centers. Plants possess defense mechanisms to protect against pathogen attack. Inducible plant defense is controlled by signal transduction pathways, inducible promoters and cis-regulatory elements corresponding to key genes involved in defense, and pathogen-specific responses. Identified inducible promoters and cis-acting elements could be utilized in plant sentinels, or ‘phytosensors’, by fusing these to reporter genes to produce plants with altered phenotypes in response to the presence of pathogens. Here, we have employed cis-acting elements from promoter regions of pathogen inducible genes as well as those responsive to the plant defense signal molecules salicylic acid, jasmonic acid, and ethylene. Synthetic promoters were constructed by combining various regulatory elements supplemented with the enhancer elements from the Cauliflower mosaic virus (CaMV) 35S promoter to increase basal level of the GUS expression. The inducibility of each synthetic promoter was first assessed in transient expression assays using Arabidopsis thaliana protoplasts and then examined for efficacy in stably transgenic Arabidopsis and tobacco plants. Histochemical and fluorometric GUS expression analyses showed that both transgenic Arabidopsis and tobacco plants responded to elicitor and phytohormone treatments with increased GUS expression when compared to untreated plants. Pathogen-inducible phytosensor studies were initiated by analyzing the sensitivity of the synthetic promoters against virus infection. Transgenic tobacco plants infected with Alfalfa mosaic virus showed an increase in GUS expression when compared to mock-inoculated control plants, whereas Tobacco mosaic virus infection caused no changes in GUS expression. Further research, using these transgenic plants against a range of different pathogens with the regulation of detectable reporter gene could provide biological evidence to define the functional differences between pathogens, and provide new technology and applications for transgenic plants as phytosensors. PMID:27879840

Disease Management in the Genomics Era-Summaries of Focus Issue Papers.

PubMed

Klosterman, S J; Rollins, J R; Sudarshana, M R; Vinatzer, B A

2016-10-01

The genomics revolution has contributed enormously to research and disease management applications in plant pathology. This development has rapidly increased our understanding of the molecular mechanisms underpinning pathogenesis and resistance, contributed novel markers for rapid pathogen detection and diagnosis, and offered further insights into the genetics of pathogen populations on a larger scale. The availability of whole genome resources coupled with next-generation sequencing (NGS) technologies has helped fuel genomics-based approaches to improve disease resistance in crops. NGS technologies have accelerated the pace at which whole plant and pathogen genomes have become available, and made possible the metagenomic analysis of plant-associated microbial communities. Furthermore, NGS technologies can now be applied routinely and cost effectively to rapidly generate plant and/or pathogen genome or transcriptome marker sequences associated with virulence phenotypes in the pathogen or resistance phenotypes in the plant, potentially leading to improvements in plant disease management. In some systems, investments in plant and pathogen genomics have led to immediate, tangible benefits. This focus issue covers some of the systems. The articles in this focus issue range from overall perspective articles to research articles describing specific genomics applications for detection and control of diseases caused by nematode, viral, bacterial, fungal, and oomycete pathogens. The following are representative short summaries of the articles that appear in this Focus Issue .

THE USE OF PLANTS TO PROTECT PLANTS AND FOOD AGAINST FUNGAL PATHOGENS: A REVIEW.

PubMed

Shuping, D S S; Eloff, J N

2017-01-01

Plant fungal pathogens play a crucial role in the profitability, quality and quantity of plant production. These phytopathogens are persistent in avoiding plant defences causing diseases and quality losses around the world that amount to billions of US dollars annually. To control the scourge of plant fungal diseases, farmers have used fungicides to manage the damage of plant pathogenic fungi. Drawbacks such as development of resistance and environmental toxicity associated with these chemicals have motivated researchers and cultivators to investigate other possibilities. Several databases were accessed to determine work done on protecting plants against plant fungal pathogens with plant extracts using search terms "plant fungal pathogen", "plant extracts" and "phytopathogens". Proposals are made on the best extractants and bioassay techniques to be used. In addition to chemical fungicides, biological agents have been used to deal with plant fungal diseases. There are many examples where plant extracts or plant derived compounds have been used as commercial deterrents of fungi on a large scale in agricultural and horticultural setups. One advantage of this approach is that plant extracts usually contain more than one antifungal compound. Consequently the development of resistance of pathogens may be lower if the different compounds affect a different metabolic process. Plants cultivated using plants extracts may also be marketed as organically produced. Many papers have been published on effective antimicrobial compounds present in plant extracts focusing on applications in human health. More research is required to develop suitable, sustainable, effective, cheaper botanical products that can be used to help overcome the scourge of plant fungal diseases. Scientists who have worked only on using plants to control human and animal fungal pathogens should consider the advantages of focusing on plant fungal pathogens. This approach could not only potentially increase food security for rural farmers, lead to commercial rewards, but it is also much easier to test the efficacy in greenhouse or field experiments. Even if extracts are toxic it may still be useful in the floriculture industry.

Draft genome sequence of Fusicladium effusum, cause of pecan scab

USDA-ARS?s Scientific Manuscript database

Pecan scab, caused by the plant pathogenic fungus Fusicladium effusum, is the most destructive disease of pecan, an important specialty crop cultivated in several regions of the world. At this time, no other members of the family Venturiaceae (in which the pathogen resides) have been reported sequen...

Can Plant Viruses Cross the Kingdom Border and Be Pathogenic to Humans?

PubMed Central

Balique, Fanny; Lecoq, Hervé; Raoult, Didier; Colson, Philippe

2015-01-01

Phytoviruses are highly prevalent in plants worldwide, including vegetables and fruits. Humans, and more generally animals, are exposed daily to these viruses, among which several are extremely stable. It is currently accepted that a strict separation exists between plant and vertebrate viruses regarding their host range and pathogenicity, and plant viruses are believed to infect only plants. Accordingly, plant viruses are not considered to present potential pathogenicity to humans and other vertebrates. Notwithstanding these beliefs, there are many examples where phytoviruses circulate and propagate in insect vectors. Several issues are raised here that question if plant viruses might further cross the kingdom barrier to cause diseases in humans. Indeed, there is close relatedness between some plant and animal viruses, and almost identical gene repertoires. Moreover, plant viruses can be detected in non-human mammals and humans samples, and there are evidence of immune responses to plant viruses in invertebrates, non-human vertebrates and humans, and of the entry of plant viruses or their genomes into non-human mammal cells and bodies after experimental exposure. Overall, the question raised here is unresolved, and several data prompt the additional extensive study of the interactions between phytoviruses and non-human mammals and humans, and the potential of these viruses to cause diseases in humans. PMID:25903834

Identification of the infection route of a Fusarium seed pathogen into nondormant Bromus tectorum seeds

Treesearch

JanaLynn Franke; Brad Geary; Susan E. Meyer

2014-01-01

The genus Fusarium has a wide host range and causes many different forms of plant disease. These include seed rot and seedling blight diseases of cultivated plants. The diseases caused by Fusarium on wild plants are less well-known. In this study, we examined disease development caused by Fusarium sp. n on nondormant seeds of the important rangeland weed Bromus...

Cytokinins for immunity beyond growth, galls and green islands.

PubMed

Naseem, Muhammad; Wölfling, Mirko; Dandekar, Thomas

2014-08-01

Cytokinins are essential plant hormones that control almost every aspect of plant growth and development. Their function in mediating plant susceptibility to fungal biotrophs and gall-causing pathogens is well known. Here we highlight the interaction between cytokinins and salicylic acid pathways. Furthermore, we discuss ways in which cytokinin signaling could crosstalk with plant immune networks. Some of these networks are modulated by pathogens to propagate disease, whereas others help the host to mitigate an infection. Copyright © 2014 Elsevier Ltd. All rights reserved.

Occurrence of Root Rot and Vascular Wilt Diseases in Roselle (Hibiscus sabdariffa L.) in Upper Egypt

PubMed Central

Hassan, Naglaa; Shimizu, Masafumi

2014-01-01

Roselle (Hibiscus sabdariffa L.) family Malvaceae is an important crop used in food, cosmetics and pharmaceutics industries. Roselle is cultivated mainly in Upper Egypt (Qena and Aswan governorates) producing 94% of total production. Root rot disease of roselle is one of the most important diseases that attack both seedlings and adult plants causing serious losses in crop productivity and quality. The main objective of the present study is to identify and characterize pathogens associated with root rot and wilt symptoms of roselle in Qena, Upper Egypt and evaluate their pathogenicity under greenhouse and field condition. Fusarium oxysporum, Macrophomina phaseolina, Fusarium solani, Fusarium equiseti and Fusarium semitectum were isolated from the natural root rot diseases in roselle. All isolated fungi were morphologically characterized and varied in their pathogenic potentialities. They could attack roselle plants causing damping-off and root rot/wilt diseases in different pathogenicity tests. The highest pathogenicity was caused by F. oxysporum and M. phaseolina followed by F. solani. The least pathogenic fungi were F. equiseti followed by F. semitectum. It obviously noted that Baladi roselle cultivar was more susceptible to infection with all tested fungi than Sobhia 17 under greenhouse and field conditions. This is the first report of fungal pathogens causing root rot and vascular wilt in roselle in Upper Egypt. PMID:24808737

The sterol-binding activity of PATHOGENESIS-RELATED PROTEIN 1 reveals the mode of action of an antimicrobial protein.

PubMed

Gamir, Jordi; Darwiche, Rabih; Van't Hof, Pieter; Choudhary, Vineet; Stumpe, Michael; Schneiter, Roger; Mauch, Felix

2017-02-01

Pathogenesis-related proteins played a pioneering role 50 years ago in the discovery of plant innate immunity as a set of proteins that accumulated upon pathogen challenge. The most abundant of these proteins, PATHOGENESIS-RELATED 1 (PR-1) encodes a small antimicrobial protein that has become, as a marker of plant immune signaling, one of the most referred to plant proteins. The biochemical activity and mode of action of PR-1 proteins has remained elusive, however. Here, we provide genetic and biochemical evidence for the capacity of PR-1 proteins to bind sterols, and demonstrate that the inhibitory effect on pathogen growth is caused by the sequestration of sterol from pathogens. In support of our findings, sterol-auxotroph pathogens such as the oomycete Phytophthora are particularly sensitive to PR-1, whereas sterol-prototroph fungal pathogens become highly sensitive only when sterol biosynthesis is compromised. Our results are in line with previous findings showing that plants with enhanced PR-1 expression are particularly well protected against oomycete pathogens. © 2016 The Authors The Plant Journal © 2016 John Wiley & Sons Ltd.

Isocitrate Lyase Is Essential for Pathogenicity of the Fungus Leptosphaeria maculans to Canola (Brassica napus)

PubMed Central

Idnurm, Alexander; Howlett, Barbara J.

2002-01-01

A pathogenicity gene has been identified in Leptosphaeria maculans, the ascomycetous fungus that causes blackleg disease of canola (Brassica napus). This gene encodes isocitrate lyase, a component of the glyoxylate cycle, and is essential for the successful colonization of B. napus. It was identified by a reverse genetics approach whereby a plasmid conferring hygromycin resistance was inserted randomly into the L. maculans genome. Twelve of 516 transformants tested had reduced pathogenicity on cotyledons of B. juncea and B. napus, and 1 of these 12 had a deletion of the isocitrate lyase gene, as well as an insertion of the hygromycin resistance gene. This mutant was unable to grow on fatty acids, including monolaurate, and the isocitrate lyase transcript was not detected. When the wild-type gene was reintroduced into the mutant, growth on monolaurate was restored and pathogenicity was partially restored. L. maculans isocitrate lyase is produced during infection of B. napus cotyledons, while the plant homologue is not. When 2.5% glucose was added to the inoculum of the isocitrate lyase mutant, lesions of sizes similar to those caused by wild-type isolate M1 developed on B. napus cotyledons. These findings suggest that the glyoxylate pathway is essential for disease development by this plant-pathogenic fungus, as has been shown recently for a fungal and bacterial pathogen of animals and a bacterial pathogen of plants. Involvement of the glyoxylate pathway in pathogenesis in animals and plants presents potential drug targets for control of diseases. PMID:12455691

Effect of different ecological conditions on secondary metabolite production and gene expression in two mycotoxigenic plant pathogen Fusarium species: F. verticillioides and F. equiseti

USDA-ARS?s Scientific Manuscript database

The genus Fusarium includes many species that are plant pathogens and many produce harmful secondary metabolites including fumonisins and trichothecenes. These mycotoxins can cause disease in animals and have been associated with cancers and birth defects in humans. Many factors influence the produc...

Impact of Vector Dispersal and Host-Plant Fidelity on the Dissemination of an Emerging Plant Pathogen

PubMed Central

Johannesen, Jes; Foissac, Xavier; Kehrli, Patrik; Maixner, Michael

2012-01-01

Dissemination of vector-transmitted pathogens depend on the survival and dispersal of the vector and the vector's ability to transmit the pathogen, while the host range of vector and pathogen determine the breath of transmission possibilities. In this study, we address how the interaction between dispersal and plant fidelities of a pathogen (stolbur phytoplasma tuf-a) and its vector (Hyalesthes obsoletus: Cixiidae) affect the emergence of the pathogen. Using genetic markers, we analysed the geographic origin and range expansion of both organisms in Western Europe and, specifically, whether the pathogen's dissemination in the northern range is caused by resident vectors widening their host-plant use from field bindweed to stinging nettle, and subsequent host specialisation. We found evidence for common origins of pathogen and vector south of the European Alps. Genetic patterns in vector populations show signals of secondary range expansion in Western Europe leading to dissemination of tuf-a pathogens, which might be newly acquired and of hybrid origin. Hence, the emergence of stolbur tuf-a in the northern range was explained by secondary immigration of vectors carrying stinging nettle-specialised tuf-a, not by widening the host-plant spectrum of resident vectors with pathogen transmission from field bindweed to stinging nettle nor by primary co-migration from the resident vector's historical area of origin. The introduction of tuf-a to stinging nettle in the northern range was therefore independent of vector's host-plant specialisation but the rapid pathogen dissemination depended on the vector's host shift, whereas the general dissemination elsewhere was linked to plant specialisation of the pathogen but not of the vector. PMID:23284774

Impact of vector dispersal and host-plant fidelity on the dissemination of an emerging plant pathogen.

PubMed

Johannesen, Jes; Foissac, Xavier; Kehrli, Patrik; Maixner, Michael

2012-01-01

Dissemination of vector-transmitted pathogens depend on the survival and dispersal of the vector and the vector's ability to transmit the pathogen, while the host range of vector and pathogen determine the breath of transmission possibilities. In this study, we address how the interaction between dispersal and plant fidelities of a pathogen (stolbur phytoplasma tuf-a) and its vector (Hyalesthes obsoletus: Cixiidae) affect the emergence of the pathogen. Using genetic markers, we analysed the geographic origin and range expansion of both organisms in Western Europe and, specifically, whether the pathogen's dissemination in the northern range is caused by resident vectors widening their host-plant use from field bindweed to stinging nettle, and subsequent host specialisation. We found evidence for common origins of pathogen and vector south of the European Alps. Genetic patterns in vector populations show signals of secondary range expansion in Western Europe leading to dissemination of tuf-a pathogens, which might be newly acquired and of hybrid origin. Hence, the emergence of stolbur tuf-a in the northern range was explained by secondary immigration of vectors carrying stinging nettle-specialised tuf-a, not by widening the host-plant spectrum of resident vectors with pathogen transmission from field bindweed to stinging nettle nor by primary co-migration from the resident vector's historical area of origin. The introduction of tuf-a to stinging nettle in the northern range was therefore independent of vector's host-plant specialisation but the rapid pathogen dissemination depended on the vector's host shift, whereas the general dissemination elsewhere was linked to plant specialisation of the pathogen but not of the vector.

Starch Hydrolysis and Vessel Occlusion Related to Wilt Symptoms in Olive Stems of Susceptible Cultivars Infected by Verticillium dahliae

PubMed Central

Trapero, Carlos; Alcántara, Esteban; Jiménez, Jaime; Amaro-Ventura, María C.; Romero, Joaquín; Koopmann, Birger; Karlovsky, Petr; von Tiedemann, Andreas; Pérez-Rodríguez, Mario; López-Escudero, Francisco J.

2018-01-01

This study investigated starch content, amount of pathogen DNA and density of occluded vessels in healthy and Verticillium dahliae infected olive shoots and stems. Starch hydrolysis is considered a mechanism to refill xylem vessels that suffered cavitation by either, drought conditions or pathogen infections. The main objective of this work was to evaluate this mechanism in olive plants subjected to V. dahliae infection or to drought conditions, in order to know the importance of cavitation in the development of wilting symptoms. In initial experiments starch content in the shoots was studied in trees of cultivars differing in the level of resistance growing in fields naturally infested with V. dahliae. The starch content, esteemed by microscopic observation of stem transversal sections stained with lugol, decreased with the level of symptom severity. Results were confirmed in a new experiment developed with young plants of cultivars ‘Picual’ (highly susceptible), ‘Arbequina’ (moderately susceptible) and ‘Frantoio’ (resistant), growing in pots under greenhouse conditions, either inoculated or not with V. dahliae. In this experiment, the pathogen DNA content, quantified by real-time PCR, and the density of occluded vessels, recorded by microscopic observations of transversal sections stained with toluidine blue, were related to the symptoms severity caused by the pathogen. Finally, a drought experiment was established with young plants of the cultivar ‘Picual’ grown in pots under greenhouse conditions in order to compare the effects caused by water deficit with those caused by the pathogen infection. In both cases, results show that starch hydrolysis occurred, what indirectly evidence the importance of xylem cavitation in the development of the symptoms caused by V. dahliae but in the water stressed plants no vessel occlusion was detected. PMID:29445388

Evolution of Compatibility Range in the Rice-Magnaporthe oryzae System: An Uneven Distribution of R Genes Between Rice Subspecies.

PubMed

Gallet, Romain; Fontaine, Colin; Bonnot, François; Milazzo, Joëlle; Tertois, Christophe; Adreit, Henri; Ravigné, Virginie; Fournier, Elisabeth; Tharreau, Didier

2016-04-01

Efficient strategies for limiting the impact of pathogens on crops require a good understanding of the factors underlying the evolution of compatibility range for the pathogens and host plants, i.e., the set of host genotypes that a particular pathogen genotype can infect and the set of pathogen genotypes that can infect a particular host genotype. Until now, little is known about the evolutionary and ecological factors driving compatibility ranges in systems implicating crop plants. We studied the evolution of host and pathogen compatibility ranges for rice blast disease, which is caused by the ascomycete Magnaporthe oryzae. We challenged 61 rice varieties from three rice subspecies with 31 strains of M. oryzae collected worldwide from all major known genetic groups. We determined the compatibility range of each plant variety and pathogen genotype and the severity of each plant-pathogen interaction. Compatibility ranges differed between rice subspecies, with the most resistant subspecies selecting for pathogens with broader compatibility ranges and the least resistant subspecies selecting for pathogens with narrower compatibility ranges. These results are consistent with a nested distribution of R genes between rice subspecies.

The effect of tar spot pathogen on host plant carbon balance and its possible consequences on a tundra ecosystem.

PubMed

Masumoto, Shota; Uchida, Masaki; Tojo, Motoaki; Herrero, Maria Luz; Mori, Akira S; Imura, Satoshi

2018-03-01

In Arctic tundra, plant pathogens have substantial effects on the growth and survival of hosts, and impacts on the carbon balance at the scale of ecological systems. To understand these effects on carbon dynamics across different scales including plant organ, individual, population and ecosystem, we focused on two primary factors: host productivity reduction and carbon consumption by the pathogen. We measured the effect of the pathogen on photosynthetic and respiratory activity in the host. We also measured respiration and the amount of carbon in the pathogen. We constructed a model based on these two factors, and calculated pathogenic effects on the carbon balance at different organismal and ecological scales. We found that carbon was reduced in infected leaves by 118% compared with healthy leaves; the major factor causing this loss was pathogenic carbon consumption. The carbon balance at the population and ecosystem levels decreased by 35% and 20%, respectively, at an infection rate of 30%. This case study provides the first evidence that a host plant can lose more carbon through pathogenic carbon consumption than through a reduction in productivity. Such a pathogenic effect could greatly change ecosystem carbon cycling without decreasing annual productivity.

Host-Induced Silencing of Pathogenicity Genes Enhances Resistance to Fusarium oxysporum Wilt in Tomato.

PubMed

Bharti, Poonam; Jyoti, Poonam; Kapoor, Priya; Sharma, Vandana; Shanmugam, V; Yadav, Sudesh Kumar

2017-08-01

This study presents a novel approach of controlling vascular wilt in tomato by RNAi expression directed to pathogenicity genes of Fusarium oxysporum f. sp. lycopersici. Vascular wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici leads to qualitative and quantitative loss of the crop. Limitation in the existing control measures necessitates the development of alternative strategies to increase resistance in the plants against pathogens. Recent findings paved way to RNAi, as a promising method for silencing of pathogenicity genes in fungus and provided effective resistance against fungal pathogens. Here, two important pathogenicity genes FOW2, a Zn(II)2Cys6 family putative transcription regulator, and chsV, a putative myosin motor and a chitin synthase domain, were used for host-induced gene silencing through hairpinRNA cassettes of these genes against Fusarium oxysporum f. sp. lycopersici. HairpinRNAs were assembled in appropriate binary vectors and transformed into tomato plant targeting FOW2 and chsV genes, for two highly pathogenic strains of Fusarium oxysporum viz. TOFOL-IHBT and TOFOL-IVRI. Transgenic tomatoes were analyzed for possible attainment of resistance in transgenic lines against fungal infection. Eight transgenic lines expressing hairpinRNA cassettes showed trivial disease symptoms after 6-8 weeks of infection. Hence, the host-induced posttranscriptional gene silencing of pathogenicity genes in transgenic tomato plants has enhanced their resistance to vascular wilt disease caused by Fusarium oxysporum.

Necrotrophic pathogens use the salicylic acid signaling pathway to promote disease development in tomato.

PubMed

Rahman, Taha Abd El; Oirdi, Mohamed El; Gonzalez-Lamothe, Rocio; Bouarab, Kamal

2012-12-01

Plants use different immune pathways to combat pathogens. The activation of the jasmonic acid (JA)-signaling pathway is required for resistance against necrotrophic pathogens; however, to combat biotrophic pathogens, the plants activate mainly the salicylic acid (SA)-signaling pathway. SA can antagonize JA signaling and vice versa. NPR1 (noninducible pathogenesis-related 1) is considered a master regulator of SA signaling. NPR1 interacts with TGA transcription factors, ultimately leading to the activation of SA-dependent responses. SA has been shown to promote disease development caused by the necrotrophic pathogen Botrytis cinerea through NPR1, by suppressing the expression of two JA-dependent defense genes, proteinase inhibitors I and II. We show here that the transcription factor TGA1.a contributes to disease development caused by B. cinerea in tomato by suppressing the expression of proteinase inhibitors I and II. Finally, we present evidence that the SA-signaling pathway contributes to disease development caused by another necrotrophic pathogen, Alternaria solani, in tomato. Disease development promoted by SA through NPR1 requires the TGA1.a transcription factor. These data highlight how necrotrophs manipulate the SAsignaling pathway to promote their disease in tomato.

Pythium invasion of plant-based life support systems: biological control and sources

NASA Technical Reports Server (NTRS)

Jenkins, D. G.; Cook, K. L.; Garland, J. L.; Board, K. F.; Sager, J. C. (Principal Investigator)

2000-01-01

Invasion of plant-based life support systems by plant pathogens could cause plant disease and disruption of life support capability. Root rot caused by the fungus, Pythium, was observed during tests of prototype plant growth systems containing wheat at the Kennedy Space Center (KSC). We conducted experiments to determine if the presence of complex microbial communities in the plant root zone (rhizosphere) resisted invasion by the Pythium species isolated from the wheat root. Rhizosphere inocula of different complexity (as assayed by community-level physiological profile: CLPP) were developed using a dilution/extinction approach, followed by growth in hydroponic rhizosphere. Pythium growth on wheat roots and concomitant decreases in plant growth were inversely related to the complexity of the inocula during 20-day experiments in static hydroponic systems. Pythium was found on the seeds of several different wheat cultivars used in controlled environmental studies, but it is unclear if the seed-borne fungal strain(s) were identical to the pathogenic strain recovered from the KSC studies. Attempts to control pathogens and their effects in hydroponic life support systems should include early inoculation with complex microbial communities, which is consistent with ecological theory.

Real time expression of ACC oxidase and PR-protein genes mediated by Methylobacterium spp. in tomato plants challenged with Xanthomonas campestris pv. vesicatoria.

PubMed

Yim, W J; Kim, K Y; Lee, Y W; Sundaram, S P; Lee, Y; Sa, T M

2014-07-15

Biotic stress like pathogenic infection increases ethylene biosynthesis in plants and ethylene inhibitors are known to alleviate the severity of plant disease incidence. This study aimed to reduce the bacterial spot disease incidence in tomato plants caused by Xanthomonas campestris pv. vesicatoria (XCV) by modulating stress ethylene with 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity of Methylobacterium strains. Under greenhouse condition, Methylobacterium strains inoculated and pathogen challenged tomato plants had low ethylene emission compared to pathogen infected ones. ACC accumulation and ACC oxidase (ACO) activity with ACO related gene expression increased in XCV infected tomato plants over Methylobacterium strains inoculated plants. Among the Methylobacterium spp., CBMB12 resulted lowest ACO related gene expression (1.46 Normalized Fold Expression), whereas CBMB20 had high gene expression (3.42 Normalized Fold Expression) in pathogen challenged tomato. But a significant increase in ACO gene expression (7.09 Normalized Fold Expression) was observed in the bacterial pathogen infected plants. In contrast, Methylobacterium strains enhanced β-1,3-glucanase and phenylalanine ammonia-lyase (PAL) enzyme activities in pathogen challenged tomato plants. The respective increase in β-1,3-glucanase related gene expressions due to CBMB12, CBMB15, and CBMB20 strains were 66.3, 25.5 and 10.4% higher over pathogen infected plants. Similarly, PAL gene expression was high with 0.67 and 0.30 Normalized Fold Expression, in pathogen challenged tomato plants inoculated with CBMB12 and CBMB15 strains. The results suggest that ethylene is a crucial factor in bacterial spot disease incidence and that methylobacteria with ACC deaminase activity can reduce the disease severity with ultimate pathogenesis-related protein increase in tomato. Copyright © 2014 Elsevier GmbH. All rights reserved.

A Single, Plastic Population of Mycosphaerella pinodes Causes Ascochyta Blight on Winter and Spring Peas (Pisum sativum) in France

PubMed Central

Guibert, Michèle; Leclerc, Aurélie; Andrivon, Didier; Tivoli, Bernard

2012-01-01

Plant diseases are caused by pathogen populations continuously subjected to evolutionary forces (genetic flow, selection, and recombination). Ascochyta blight, caused by Mycosphaerella pinodes, is one of the most damaging necrotrophic pathogens of field peas worldwide. In France, both winter and spring peas are cultivated. Although these crops overlap by about 4 months (March to June), primary Ascochyta blight infections are not synchronous on the two crops. This suggests that the disease could be due to two different M. pinodes populations, specialized on either winter or spring pea. To test this hypothesis, 144 pathogen isolates were collected in the field during the winter and spring growing seasons in Rennes (western France), and all the isolates were genotyped using amplified fragment length polymorphism (AFLP) markers. Furthermore, the pathogenicities of 33 isolates randomly chosen within the collection were tested on four pea genotypes (2 winter and 2 spring types) grown under three climatic regimes, simulating winter, late winter, and spring conditions. M. pinodes isolates from winter and spring peas were genetically polymorphic but not differentiated according to the type of cultivars. Isolates from winter pea were more pathogenic than isolates from spring pea on hosts raised under winter conditions, while isolates from spring pea were more pathogenic than those from winter pea on plants raised under spring conditions. These results show that disease developed on winter and spring peas was initiated by a single population of M. pinodes whose pathogenicity is a plastic trait modulated by the physiological status of the host plant. PMID:23023742

The plant nitrogen mobilization promoted by Colletotrichum lindemuthianum in Phaseolus leaves depends on fungus pathogenicity.

PubMed

Tavernier, Virginie; Cadiou, Sandrine; Pageau, Karine; Laugé, Richard; Reisdorf-Cren, Michèle; Langin, Thierry; Masclaux-Daubresse, Céline

2007-01-01

Nitrogen plays an essential role in the nutrient relationship between plants and pathogens. Some studies report that the nitrogen-mobilizing plant metabolism that occurs during abiotic and biotic stress could be a 'slash-and-burn' defence strategy. In order to study nitrogen recycling and mobilization in host plants during pathogen attack and invasion, the Colletotrichum lindemuthianum/Phaseolus vulgaris interaction was used as a model. C. lindemuthianum is a hemibiotroph that causes anthracnose disease on P. vulgaris. Non-pathogenic mutants and the pathogenic wild-type strain were used to compare their effects on plant metabolism. The deleterious effects of infection were monitored by measuring changes in chlorophyll, protein, and amino acid concentrations. It was shown that amino acid composition changed depending on the plant-fungus interaction and that glutamine accumulated mainly in the leaves infected by the pathogenic strain. Glutamine accumulation correlated with the accumulation of cytosolic glutamine synthetase (GS1 alpha) mRNA. The most striking result was that the GS1 alpha gene was induced in all the fungus-infected leaves, independent of the strain used for inoculation, and that GS1 alpha expression paralleled the PAL3 and CHS defence gene expression. It is concluded that a role of GS1 alpha in plant defence has to be considered.

A genomic approach to the understanding of Xylella fastidiosa pathogenicity.

PubMed

Lambais, M R; Goldman, M H; Camargo, L E; Goldman, G H

2000-10-01

Xylella fastidiosa is a fastidious, xylem-limited bacterium that causes several economically important plant diseases, including citrus variegated chlorosis (CVC). X. fastidiosa is the first plant pathogen to have its genome completely sequenced. In addition, it is probably the least previously studied of any organism for which the complete genome sequence is available. Several pathogenicity-related genes have been identified in the X. fastidiosa genome by similarity with other bacterial genes involved in pathogenesis in plants, as well as in animals. The X. fastidiosa genome encodes different classes of proteins directly or indirectly involved in cell-cell interactions, degradation of plant cell walls, iron homeostasis, anti-oxidant responses, synthesis of toxins, and regulation of pathogenicity. Neither genes encoding members of the type III protein secretion system nor avirulence-like genes have been identified in X. fastidiosa.

Recognition of bacterial plant pathogens: local, systemic and transgenerational immunity.

PubMed

Henry, Elizabeth; Yadeta, Koste A; Coaker, Gitta

2013-09-01

Bacterial pathogens can cause multiple plant diseases and plants rely on their innate immune system to recognize and actively respond to these microbes. The plant innate immune system comprises extracellular pattern recognition receptors that recognize conserved microbial patterns and intracellular nucleotide binding leucine-rich repeat (NLR) proteins that recognize specific bacterial effectors delivered into host cells. Plants lack the adaptive immune branch present in animals, but still afford flexibility to pathogen attack through systemic and transgenerational resistance. Here, we focus on current research in plant immune responses against bacterial pathogens. Recent studies shed light onto the activation and inactivation of pattern recognition receptors and systemic acquired resistance. New research has also uncovered additional layers of complexity surrounding NLR immune receptor activation, cooperation and sub-cellular localizations. Taken together, these recent advances bring us closer to understanding the web of molecular interactions responsible for coordinating defense responses and ultimately resistance. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.

Monitoring streams and stormwater ponds for early detection of oomycete plant pathogens in western Washington, a citizen science project

Treesearch

Marianne Elliott; Lucy Rollins; Gary Chastagner

2017-01-01

Sudden Oak Death (SOD) is the common name for a disease caused by Phytophthora ramorum (oomycetes), an invasive plant pathogen of regulatory concern. The nursery, timber, forest specialty product, and Christmas tree industries in Washington are at risk because of the spread of P. ramorum within nurseries and from nurseries into...

Constitutive expression of the xylanase inhibitor TAXI-III delays Fusarium head blight symptoms in durum wheat transgenic plants.

PubMed

Moscetti, Ilaria; Tundo, Silvio; Janni, Michela; Sella, Luca; Gazzetti, Katia; Tauzin, Alexandra; Giardina, Thierry; Masci, Stefania; Favaron, Francesco; D'Ovidio, Renato

2013-12-01

Cereals contain xylanase inhibitor (XI) proteins which inhibit microbial xylanases and are considered part of the defense mechanisms to counteract microbial pathogens. Nevertheless, in planta evidence for this role has not been reported yet. Therefore, we produced a number of transgenic plants constitutively overexpressing TAXI-III, a member of the TAXI type XI that is induced by pathogen infection. Results showed that TAXI-III endows the transgenic wheat with new inhibition capacities. We also showed that TAXI-III is correctly secreted into the apoplast and possesses the expected inhibition parameters against microbial xylanases. The new inhibition properties of the transgenic plants correlate with a significant delay of Fusarium head blight disease symptoms caused by Fusarium graminearum but do not significantly influence leaf spot symptoms caused by Bipolaris sorokiniana. We showed that this contrasting result can be due to the different capacity of TAXI-III to inhibit the xylanase activity of these two fungal pathogens. These results provide, for the first time, clear evidence in planta that XI are involved in plant defense against fungal pathogens and show the potential to manipulate TAXI-III accumulation to improve wheat resistance against F. graminearum.

Xylella fastidiosa: an examination of a re-emerging plant pathogen.

PubMed

Rapicavoli, Jeannette; Ingel, Brian; Blanco-Ulate, Barbara; Cantu, Dario; Roper, Caroline

2018-04-01

Xylella fastidiosa is a Gram-negative bacterial plant pathogen with an extremely wide host range. This species has recently been resolved into subspecies that correlate with host specificity. This review focuses on the status of X. fastidiosa pathogenic associations in plant hosts in which the bacterium is either endemic or has been recently introduced. Plant diseases associated with X. fastidiosa have been documented for over a century, and much about what is known in the context of host-pathogen interactions is based on these hosts, such as grape and citrus, in which this pathogen has been well described. Recent attention has focused on newly emerging X. fastidiosa diseases, such as in olives. Bacteria; Gammaproteobacteria; family Xanthomonadaceae; genus Xylella; species fastidiosa. Gram-negative rod (0.25-0.35 × 0.9-3.5 μm), non-flagellate, motile via Type IV pili-mediated twitching, fastidious. Xylella fastidiosa has a broad host range that includes ornamental, ecological and agricultural plants belonging to over 300 different species in 63 different families. To date, X. fastidiosa has been found to be pathogenic in over 100 plant species. In addition, it can establish non-symptomatic associations with many plants as a commensal endophyte. Here, we list the four distinct subspecies of X. fastidiosa and some of the agriculturally relevant diseases caused by them: X. fastidiosa ssp. fastidiosa causes Pierce's disease (PD) of grapevine (Vitis vinifera); X. fastidiosa ssp. multiplex causes almond leaf scorch (ALS) and diseases on other nut and shade tree crops; X. fastidiosa ssp. pauca causes citrus variegated chlorosis (CVC) (Citrus spp.), coffee leaf scorch and olive quick decline syndrome (OQDS) (Olea europaea); X. fastidiosa ssp. sandyi causes oleander leaf scorch (OLS) (Nerium oleander). Significant host specificity seemingly exists for some of the subspecies, although this could be a result of technical biases based on the limited number of plants tested, whereas some subspecies are not as stringent in their host range and can infect several plant hosts. Most X. fastidiosa-related diseases appear as marginal leaf necrosis and scorching of the leaves. In the case of PD, X. fastidiosa can also cause desiccation of berries (termed 'raisining'), irregular periderm development and abnormal abscission of petioles. In olive trees affected with OQDS, leaves exhibit marginal necrosis and defoliation, and overall tree decline occurs. Plants with ALS and OLS also exhibit the characteristic leaf scorch symptoms. Not all X. fastidiosa-related diseases exhibit the typical leaf scorch symptoms. These include CVC and Phony Peach disease, amongst others. In the case of CVC, symptoms include foliar wilt and interveinal chlorosis on the upper surfaces of the leaves (similar to zinc deficiency), which correspond to necrotic, gum-like regions on the undersides of the leaves. Additional symptoms of CVC include defoliation, dieback and hardening of fruits. Plants infected with Phony Peach disease exhibit a denser, more compact canopy (as a result of shortened internodes, darker green leaves and delayed leaf senescence), premature bloom and reduced fruit size. Some occlusions occur in the xylem vessels, but there are no foliar wilting, chlorosis or necrosis symptoms . USEFUL WEBSITES: http://www.piercesdisease.org/; https://pubmlst.org/xfastidiosa/; http://www.xylella.lncc.br/; https://nature.berkeley.edu/xylella/; https://ec.europa.eu/food/plant/plant_health_biosecurity/legislation/emergency_measures/xylella-fastidiosa_en. © 2017 BSPP AND JOHN WILEY & SONS LTD.

Biosensors for plant pathogen detection.

PubMed

Khater, Mohga; de la Escosura-Muñiz, Alfredo; Merkoçi, Arben

2017-07-15

Infectious plant diseases are caused by pathogenic microorganisms such as fungi, bacteria, viruses, viroids, phytoplasma and nematodes. Worldwide, plant pathogen infections are among main factors limiting crop productivity and increasing economic losses. Plant pathogen detection is important as first step to manage a plant disease in greenhouses, field conditions and at the country boarders. Current immunological techniques used to detect pathogens in plant include enzyme-linked immunosorbent assays (ELISA) and direct tissue blot immunoassays (DTBIA). DNA-based techniques such as polymerase chain reaction (PCR), real time PCR (RT-PCR) and dot blot hybridization have also been proposed for pathogen identification and detection. However these methodologies are time-consuming and require complex instruments, being not suitable for in-situ analysis. Consequently, there is strong interest for developing new biosensing systems for early detection of plant diseases with high sensitivity and specificity at the point-of-care. In this context, we revise here the recent advancement in the development of advantageous biosensing systems for plant pathogen detection based on both antibody and DNA receptors. The use of different nanomaterials such as nanochannels and metallic nanoparticles for the development of innovative and sensitive biosensing systems for the detection of pathogens (i.e. bacteria and viruses) at the point-of-care is also shown. Plastic and paper-based platforms have been used for this purpose, offering cheap and easy-to-use really integrated sensing systems for rapid on-site detection. Beside devices developed at research and development level a brief revision of commercially available kits is also included in this review. Copyright © 2016 Elsevier B.V. All rights reserved.

[Evaluation of Fusarium spp. pathogenicity in plant and murine models].

PubMed

Forero-Reyes, Consuelo M; Alvarado-Fernández, Angela M; Ceballos-Rojas, Ana M; González-Carmona, Lady C; Linares-Linares, Melva Y; Castañeda-Salazar, Rubiela; Pulido-Villamarín, Adriana; Góngora-Medina, Manuel E; Cortés-Vecino, Jesús A; Rodríguez-Bocanegra, María X

The genus Fusarium is widely recognized for its phytopathogenic capacity. However, it has been reported as an opportunistic pathogen in immunocompetent and immunocompromised patients. Thus, it can be considered a microorganism of interest in pathogenicity studies on different hosts. Therefore, this work evaluated the pathogenicity of Fusarium spp. isolates from different origins in plants and animals (murine hosts). Twelve isolates of Fusarium spp. from plants, animal superficial mycoses, and human superficial and systemic mycoses were inoculated in tomato, passion fruit and carnation plants, and in immunocompetent and immunosuppressed BALB/c mice. Pathogenicity tests in plants did not show all the symptoms associated with vascular wilt in the three plant models; however, colonization and necrosis of the vascular bundles, regardless of the species and origin of the isolates, showed the infective potential of Fusarium spp. in different plant species. Moreover, the pathogenicity tests in the murine model revealed behavioral changes. It was noteworthy that only five isolates (different origin and species) caused mortality. Additionally, it was observed that all isolates infected and colonized different organs, regardless of the species and origin of the isolates or host immune status. In contrast, the superficial inoculation test showed no evidence of epidermal injury or colonization. The observed results in plant and murine models suggest the pathogenic potential of Fusarium spp. isolates in different types of hosts. However, further studies on pathogenicity are needed to confirm the multihost capacity of this genus. Copyright © 2017 Asociación Argentina de Microbiología. Publicado por Elsevier España, S.L.U. All rights reserved.

Comparative Pathogenomics Reveals Horizontally Acquired Novel Virulence Genes in Fungi Infecting Cereal Hosts

PubMed Central

Gardiner, Donald M.; McDonald, Megan C.; Covarelli, Lorenzo; Solomon, Peter S.; Rusu, Anca G.; Marshall, Mhairi; Kazan, Kemal; Chakraborty, Sukumar; McDonald, Bruce A.; Manners, John M.

2012-01-01

Comparative analyses of pathogen genomes provide new insights into how pathogens have evolved common and divergent virulence strategies to invade related plant species. Fusarium crown and root rots are important diseases of wheat and barley world-wide. In Australia, these diseases are primarily caused by the fungal pathogen Fusarium pseudograminearum. Comparative genomic analyses showed that the F. pseudograminearum genome encodes proteins that are present in other fungal pathogens of cereals but absent in non-cereal pathogens. In some cases, these cereal pathogen specific genes were also found in bacteria associated with plants. Phylogenetic analysis of selected F. pseudograminearum genes supported the hypothesis of horizontal gene transfer into diverse cereal pathogens. Two horizontally acquired genes with no previously known role in fungal pathogenesis were studied functionally via gene knockout methods and shown to significantly affect virulence of F. pseudograminearum on the cereal hosts wheat and barley. Our results indicate using comparative genomics to identify genes specific to pathogens of related hosts reveals novel virulence genes and illustrates the importance of horizontal gene transfer in the evolution of plant infecting fungal pathogens. PMID:23028337

Inhibiting Microbial Toxins Using Plant-Derived Compounds and Plant Extracts

PubMed Central

Upadhyay, Abhinav; Mooyottu, Shankumar; Yin, Hsinbai; Surendran Nair, Meera; Bhattaram, Varunkumar; Venkitanarayanan, Kumar

2015-01-01

Many pathogenic bacteria and fungi produce potentially lethal toxins that cause cytotoxicity or impaired cellular function either at the site of colonization or other locations in the body through receptor-mediated interactions. Various factors, including biotic and abiotic environments, competing microbes, and chemical cues affect toxin expression in these pathogens. Recent work suggests that several natural compounds can modulate toxin production in pathogenic microbes. However, studies explaining the mechanistic basis for their effect are scanty. This review discusses the potential of various plant-derived compounds for reducing toxin production in foodborne and other microbes. In addition, studies highlighting their anti-toxigenic mechanism(s) are discussed. PMID:28930207

Characterization of a tryptophan 2-monooxygenase gene from Puccinia graminis f. sp. tritici involved in auxin biosynthesis and rust pathogenicity.

PubMed

Yin, Chuntao; Park, Jeong-Jin; Gang, David R; Hulbert, Scot H

2014-03-01

The plant hormone indole-3-acetic acid (IAA) is best known as a regulator of plant growth and development but its production can also affect plant-microbe interactions. Microorganisms, including numerous plant-associated bacteria and several fungi, are also capable of producing IAA. The stem rust fungus Puccinia graminis f. sp. tritici induced wheat plants to accumulate auxin in infected leaf tissue. A gene (Pgt-IaaM) encoding a putative tryptophan 2-monooxygenase, which makes the auxin precursor indole-3-acetamide (IAM), was identified in the P. graminis f. sp. tritici genome and found to be expressed in haustoria cells in infected plant tissue. Transient silencing of the gene in infected wheat plants indicated that it was required for full pathogenicity. Expression of Pgt-IaaM in Arabidopsis caused a typical auxin expression phenotype and promoted susceptibility to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000.

Lack of host specialization on winter annual grasses in the fungal seed bank pathogen Pyrenophora semeniperda

Treesearch

Julie Beckstead; Susan E. Meyer; Toby S. Ishizuka; Kelsey M. McEvoy; Craig E. Coleman

2016-01-01

Generalist plant pathogens may have wide host ranges, but many exhibit varying degrees of host specialization, with multiple pathogen races that have narrower host ranges. These races are often genetically distinct, with each race causing highest disease incidence on its host of origin. We examined host specialization in the seed pathogen Pyrenophora...

Arabidopsis and Brachypodium distachyon Transgenic Plants Expressing Aspergillus nidulans Acetylesterases Have Decreased Degree of Polysaccharide Acetylation and Increased Resistance to Pathogens1[C][W][OA

PubMed Central

Pogorelko, Gennady; Lionetti, Vincenzo; Fursova, Oksana; Sundaram, Raman M.; Qi, Mingsheng; Whitham, Steven A.; Bogdanove, Adam J.; Bellincampi, Daniela; Zabotina, Olga A.

2013-01-01

The plant cell wall has many significant structural and physiological roles, but the contributions of the various components to these roles remain unclear. Modification of cell wall properties can affect key agronomic traits such as disease resistance and plant growth. The plant cell wall is composed of diverse polysaccharides often decorated with methyl, acetyl, and feruloyl groups linked to the sugar subunits. In this study, we examined the effect of perturbing cell wall acetylation by making transgenic Arabidopsis (Arabidopsis thaliana) and Brachypodium (Brachypodium distachyon) plants expressing hemicellulose- and pectin-specific fungal acetylesterases. All transgenic plants carried highly expressed active Aspergillus nidulans acetylesterases localized to the apoplast and had significant reduction of cell wall acetylation compared with wild-type plants. Partial deacetylation of polysaccharides caused compensatory up-regulation of three known acetyltransferases and increased polysaccharide accessibility to glycosyl hydrolases. Transgenic plants showed increased resistance to the fungal pathogens Botrytis cinerea and Bipolaris sorokiniana but not to the bacterial pathogens Pseudomonas syringae and Xanthomonas oryzae. These results demonstrate a role, in both monocot and dicot plants, of hemicellulose and pectin acetylation in plant defense against fungal pathogens. PMID:23463782

Hitchhiker's guide to multi-dimensional plant pathology.

PubMed

Saunders, Diane G O

2015-02-01

Filamentous pathogens pose a substantial threat to global food security. One central question in plant pathology is how pathogens cause infection and manage to evade or suppress plant immunity to promote disease. With many technological advances over the past decade, including DNA sequencing technology, an array of new tools has become embedded within the toolbox of next-generation plant pathologists. By employing a multidisciplinary approach plant pathologists can fully leverage these technical advances to answer key questions in plant pathology, aimed at achieving global food security. This review discusses the impact of: cell biology and genetics on progressing our understanding of infection structure formation on the leaf surface; biochemical and molecular analysis to study how pathogens subdue plant immunity and manipulate plant processes through effectors; genomics and DNA sequencing technologies on all areas of plant pathology; and new forms of collaboration on accelerating exploitation of big data. As we embark on the next phase in plant pathology, the integration of systems biology promises to provide a holistic perspective of plant–pathogen interactions from big data and only once we fully appreciate these complexities can we design truly sustainable solutions to preserve our resources.

Crossover fungal pathogens: the biology and pathogenesis of fungi capable of crossing kingdoms to infect plants and humans.

PubMed

Gauthier, Gregory M; Keller, Nancy P

2013-12-01

The outbreak of fungal meningitis associated with contaminated methylprednisolone acetate has thrust the importance of fungal infections into the public consciousness. The predominant pathogen isolated from clinical specimens, Exserohilum rostratum (teleomorph: Setosphaeria rostrata), is a dematiaceous fungus that infects grasses and rarely humans. This outbreak highlights the potential for fungal pathogens to infect both plants and humans. Most crossover or trans-kingdom pathogens are soil saprophytes and include fungi in Ascomycota and Mucormycotina phyla. To establish infection, crossover fungi must overcome disparate, host-specific barriers, including protective surfaces (e.g. cuticle, skin), elevated temperature, and immune defenses. This review illuminates the underlying mechanisms used by crossover fungi to cause infection in plants and mammals, and highlights critical events that lead to human infection by these pathogens. Several genes including veA, laeA, and hapX are important in regulating biological processes in fungi important for both invasive plant and animal infections. Copyright © 2013 Elsevier Inc. All rights reserved.

Host structural carbohydrate induces vector transmission of a bacterial plant pathogen.

PubMed

Killiny, Nabil; Almeida, Rodrigo P P

2009-12-29

Many insect-borne pathogens have complex life histories because they must colonize both hosts and vectors for successful dissemination. In addition, the transition from host to vector environments may require changes in gene expression before the pathogen's departure from the host. Xylella fastidiosa is a xylem-limited plant-pathogenic bacterium transmitted by leafhopper vectors that causes diseases in a number of economically important plants. We hypothesized that factors of host origin, such as plant structural polysaccharides, are important in regulating X. fastidiosa gene expression and mediating vector transmission of this pathogen. The addition of pectin and glucan to a simple defined medium resulted in dramatic changes in X. fastidiosa's phenotype and gene-expression profile. Cells grown in the presence of pectin became more adhesive than in other media tested. In addition, the presence of pectin and glucan in media resulted in significant changes in the expression of several genes previously identified as important for X. fastidiosa's pathogenicity in plants. Furthermore, vector transmission of X. fastidiosa was induced in the presence of both polysaccharides. Our data show that host structural polysaccharides mediate gene regulation in X. fastidiosa, which results in phenotypic changes required for vector transmission. A better understanding of how vector-borne pathogens transition from host to vector, and vice versa, may lead to previously undiscovered disease-control strategies.

Evolution of an invasive species research program and implications for large-scale management of a non-native, invasive plant pathogen

Treesearch

Christopher A. Lee; Janice M. Alexander; Susan J. Frankel; Yana Valachovic

2012-01-01

We conducted a research needs assessment (RNA) in 2010 to gather opinions of "experts" and a larger public on research priorities for Phytophthora ramorum, the pathogen that causes sudden oak death in forest trees and Ramorum blight in ornamental plants. We place these 2010 findings in context with findings of similar P. ramorum...

Use of Green Fluorescent Protein-Transgenic Strains to Study Pathogenic and Nonpathogenic Lifestyles in Colletotrichum acutatum.

PubMed

Horowitz, Sigal; Freeman, Stanley; Sharon, Amir

2002-07-01

ABSTRACT Colletotrichum acutatum, which causes anthracnose disease on strawberry, can also persist on several other plant species without causing disease symptoms. The genetic and molecular bases that determine pathogenic and nonpathogenic lifestyles in C. acutatum are unclear. We developed a transformation system for C. acutatum by electroporation of germinating conidia, and transgenic isolates that express the green fluorescent protein (GFP) were produced. Details of the pathogenic and nonpathogenic lifestyles of C. acutatum were determined by using GFP-transgenic isolates. Major differences between colonization-mediating processes of strawberry and of other plants were observed. On the main host, strawberry, the germinating conidia formed branched, thick hyphae, and large numbers of appressoria were produced that were essential for plant penetration. In strawberry, the fungus developed rapidly, filling the mesophyll with dense mycelium that invaded the cells and caused necrosis of the tissue. In nonpathogenic interactions on pepper, eggplant, and tomato, the conidia germinated, producing thin, straight germ tubes. Appressoria were produced but failed to germinate and penetrate leaf tissue, resulting in epiphytic growth without invasion of the plant. Penetration of the plant occurred only several days after inoculation and was restricted to the intercellular spaces of the first cell layers of infected tissue without causing any visible damage. Much of the new fungal biomass continued to develop on the surface of inoculated organs in the nonpathogenic interaction. The differences in fungal development on strawberry compared with the other plant species suggest that signal molecules, which may be present only in strawberry, trigger appressorial germination and penetration of the primary host.

The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes

USDA-ARS?s Scientific Manuscript database

Phytophthora infestans is a destructive plant pathogen best known for causing the disease that triggered the Irish potato famine and continues to be the most costly potato pathogen to manage worldwide. Identification of its elusive center of origin is critical to understanding the mechanisms of repe...

Multi-locus tree and species tree approaches toward resolving a complex clade of downy mildews (Straminipila, Oomycota), including pathogens of beet and spinach

USDA-ARS?s Scientific Manuscript database

Accurate species determination of plant pathogens is a prerequisite for their control and quarantine, and further for assessing their potential threat to crops. The family Peronosporaceae (Straminipila; Oomycota) consists of obligate biotrophic pathogens that cause downy mildew disease on angiosperm...

Setosphaeria rostrata: Insights from the sequenced genome of Setosphaeria turcica.

PubMed

Wu, Dongliang; Turgeon, B Gillian

2013-12-01

Exserohilum rostratum, also known as Setosphaeria rostrata caused an outbreak of meningitis in 2012. S. rostrata is known as a minor pathogen of grasses and a member of the Dothideomycetes, a group that includes saprobes as well as mild to aggressive plant pathogens. A few taxa in this group, such as E. rostratum and Cochliobolus lunatus (Curvularia lunata) can be human pathogens, in favorable circumstances. Fortunately, human disease caused by E. rostratum is rare. However, the increasing number of formerly inconsequential fungi surfacing as significant pathogens demands efforts to identify determinants of crossover pathogenicity in general, and S. rostrata in particular. Very few genetic and molecular data are available for S. rostrata. The first genome sequence for any species in the genus Setosphaeria (Setosphaeria turcica) was published this year. The literature to date related to virulence determinants of S. rostrata and S. turcica to plants and a summary of S. turcica genome features that may inform future studies with the human pathogen, S. rostrata, are presented. Copyright © 2013 Elsevier Inc. All rights reserved.

Protein extraction and gel-based separation methods to analyze responses to pathogens in carnation (Dianthus caryophyllus L).

PubMed

Ardila, Harold Duban; Fernández, Raquel González; Higuera, Blanca Ligia; Redondo, Inmaculada; Martínez, Sixta Tulia

2014-01-01

We are currently using a 2-DE-based proteomics approach to study plant responses to pathogenic fungi by using the carnation (Dianthus caryophyllus L)-Fusarium oxysporum f. sp. dianthi pathosystem. It is clear that the protocols for the first stages of a standard proteomics workflow must be optimized to each biological system and objectives of the research. The optimization procedure for the extraction and separation of proteins by 1-DE and 2-DE in the indicated system is reported. This strategy can be extrapolated to other plant-pathogen interaction systems in order to perform an evaluation of the changes in the host protein profile caused by the pathogen and to identify proteins which, at early stages, are involved or implicated in the plant defense response.

Isolation of the etiological agent of primary amoebic meningoencephalitis from artificially heated waters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stevens, A.R.; Tyndall, R.L.; Coutant, C.C.

1977-12-01

To determine whether artificial heating of water by power plant discharges facilitates proliferation of the pathogenic free-living amoebae that cause primary amoebic meningoencephalitis, water samples (250 ml) were taken from discharges within 3,000 feet (ca. 914.4 m) of power plants and were processed for amoeba culture. Pathogenic Naegleria fowleri grew out of water samples from two of five lakes and rivers in Florida and from one of eight man-made lakes in Texas. Pathogenic N. fowleri did not grow from water samples taken from cooling towers and control lakes, the latter of which had no associated power plants. The identification ofmore » N. fowleri was confirmed by pathogenicity in mice and by indirect immunofluorescence analyses, by using a specific antiserum.« less

The Role of Pathogen-Secreted Proteins in Fungal Vascular Wilt Diseases

PubMed Central

de Sain, Mara; Rep, Martijn

2015-01-01

A limited number of fungi can cause wilting disease in plants through colonization of the vascular system, the most well-known being Verticillium dahliae and Fusarium oxysporum. Like all pathogenic microorganisms, vascular wilt fungi secrete proteins during host colonization. Whole-genome sequencing and proteomics screens have identified many of these proteins, including small, usually cysteine-rich proteins, necrosis-inducing proteins and enzymes. Gene deletion experiments have provided evidence that some of these proteins are required for pathogenicity, while the role of other secreted proteins remains enigmatic. On the other hand, the plant immune system can recognize some secreted proteins or their actions, resulting in disease resistance. We give an overview of proteins currently known to be secreted by vascular wilt fungi and discuss their role in pathogenicity and plant immunity. PMID:26473835

Plant-Pathogen Warfare under Changing Climate Conditions.

PubMed

Velásquez, André C; Castroverde, Christian Danve M; He, Sheng Yang

2018-05-21

Global environmental changes caused by natural and human activities have accelerated in the past 200 years. The increase in greenhouse gases is predicted to continue to raise global temperature and change water availability in the 21 st century. In this Review, we explore the profound effect the environment has on plant diseases - a susceptible host will not be infected by a virulent pathogen if the environmental conditions are not conducive for disease. The change in CO 2 concentrations, temperature, and water availability can have positive, neutral, or negative effects on disease development, as each disease may respond differently to these variations. However, the concept of disease optima could potentially apply to all pathosystems. Plant resistance pathways, including pattern-triggered immunity to effector-triggered immunity, RNA interference, and defense hormone networks, are all affected by environmental factors. On the pathogen side, virulence mechanisms, such as the production of toxins and virulence proteins, as well as pathogen reproduction and survival are influenced by temperature and humidity. For practical reasons, most laboratory investigations into plant-pathogen interactions at the molecular level focus on well-established pathosystems and use a few static environmental conditions that capture only a fraction of the dynamic plant-pathogen-environment interactions that occur in nature. There is great need for future research to increasingly use dynamic environmental conditions in order to fully understand the multidimensional nature of plant-pathogen interactions and produce disease-resistant crop plants that are resilient to climate change. Copyright © 2018 Elsevier Ltd. All rights reserved.

Genome analysis of the ubiquitous boxwood pathogen Pseudonectria foliicola: A small fungal genome with an increased cohort of genes associated with loss of virulence

USDA-ARS?s Scientific Manuscript database

Boxwood plants are affected by many different diseases caused by fungi. Some boxwood diseases are deadly and quickly kill the infected plants, but with others, the plant can survive and even thrive when infected. The fungus that causes volutella blight is the most common of these weak boxwood pathog...

Enhanced tomato disease resistance primed by arbuscular mycorrhizal fungus

PubMed Central

Song, Yuanyuan; Chen, Dongmei; Lu, Kai; Sun, Zhongxiang; Zeng, Rensen

2015-01-01

Roots of most terrestrial plants form symbiotic associations (mycorrhiza) with soil- borne arbuscular mycorrhizal fungi (AMF). Many studies show that mycorrhizal colonization enhances plant resistance against pathogenic fungi. However, the mechanism of mycorrhiza-induced disease resistance remains equivocal. In this study, we found that mycorrhizal inoculation with AMF Funneliformis mosseae significantly alleviated tomato (Solanum lycopersicum Mill.) early blight disease caused by Alternaria solani Sorauer. AMF pre-inoculation led to significant increases in activities of β-1,3-glucanase, chitinase, phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) in tomato leaves upon pathogen inoculation. Mycorrhizal inoculation alone did not influence the transcripts of most genes tested. However, pathogen attack on AMF-inoculated plants provoked strong defense responses of three genes encoding pathogenesis-related proteins, PR1, PR2, and PR3, as well as defense-related genes LOX, AOC, and PAL, in tomato leaves. The induction of defense responses in AMF pre-inoculated plants was much higher and more rapid than that in un-inoculated plants in present of pathogen infection. Three tomato genotypes: a Castlemart wild-type (WT) plant, a jasmonate (JA) biosynthesis mutant (spr2), and a prosystemin-overexpressing 35S::PS plant were used to examine the role of the JA signaling pathway in AMF-primed disease defense. Pathogen infection on mycorrhizal 35S::PS plants led to higher induction of defense-related genes and enzymes relative to WT plants. However, pathogen infection did not induce these genes and enzymes in mycorrhizal spr2 mutant plants. Bioassays showed that 35S::PS plants were more resistant and spr2 plants were more susceptible to early blight compared with WT plants. Our finding indicates that mycorrhizal colonization enhances tomato resistance to early blight by priming systemic defense response, and the JA signaling pathway is essential for mycorrhiza-primed disease resistance. PMID:26442091

Enhanced tomato disease resistance primed by arbuscular mycorrhizal fungus.

PubMed

Song, Yuanyuan; Chen, Dongmei; Lu, Kai; Sun, Zhongxiang; Zeng, Rensen

2015-01-01

Roots of most terrestrial plants form symbiotic associations (mycorrhiza) with soil- borne arbuscular mycorrhizal fungi (AMF). Many studies show that mycorrhizal colonization enhances plant resistance against pathogenic fungi. However, the mechanism of mycorrhiza-induced disease resistance remains equivocal. In this study, we found that mycorrhizal inoculation with AMF Funneliformis mosseae significantly alleviated tomato (Solanum lycopersicum Mill.) early blight disease caused by Alternaria solani Sorauer. AMF pre-inoculation led to significant increases in activities of β-1,3-glucanase, chitinase, phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) in tomato leaves upon pathogen inoculation. Mycorrhizal inoculation alone did not influence the transcripts of most genes tested. However, pathogen attack on AMF-inoculated plants provoked strong defense responses of three genes encoding pathogenesis-related proteins, PR1, PR2, and PR3, as well as defense-related genes LOX, AOC, and PAL, in tomato leaves. The induction of defense responses in AMF pre-inoculated plants was much higher and more rapid than that in un-inoculated plants in present of pathogen infection. Three tomato genotypes: a Castlemart wild-type (WT) plant, a jasmonate (JA) biosynthesis mutant (spr2), and a prosystemin-overexpressing 35S::PS plant were used to examine the role of the JA signaling pathway in AMF-primed disease defense. Pathogen infection on mycorrhizal 35S::PS plants led to higher induction of defense-related genes and enzymes relative to WT plants. However, pathogen infection did not induce these genes and enzymes in mycorrhizal spr2 mutant plants. Bioassays showed that 35S::PS plants were more resistant and spr2 plants were more susceptible to early blight compared with WT plants. Our finding indicates that mycorrhizal colonization enhances tomato resistance to early blight by priming systemic defense response, and the JA signaling pathway is essential for mycorrhiza-primed disease resistance.

Plants, plant pathogens, and microgravity--a deadly trio.

PubMed

Leach, J E; Ryba-White, M; Sun, Q; Wu, C J; Hilaire, E; Gartner, C; Nedukha, O; Kordyum, E; Keck, M; Leung, H; Guikema, J A

2001-06-01

Plants grown in spaceflight conditions are more susceptible to colonization by plant pathogens. The underlying causes for this enhanced susceptibility are not known. Possibly the formation of structural barriers and the activation of plant defense response components are impaired in spaceflight conditions. Either condition would result from altered gene expression of the plant. Because of the tools available, past studies focused on a few physiological responses or biochemical pathways. With recent advances in genomics research, new tools, including microarray technologies, are available to examine the global impact of growth in the spacecraft on the plant's gene expression profile. In ground-based studies, we have developed cDNA subtraction libraries of rice that are enriched for genes induced during pathogen infection and the defense response. Arrays of these genes are being used to dissect plant defense response pathways in a model system involving wild-type rice plants and lesion mimic mutants. The lesion mimic mutants are ideal experimental tools because they erratically develop defense response-like lesions in the absence of pathogens. The gene expression profiles from these ground-based studies will provide the molecular basis for understanding the biochemical and physiological impacts of spaceflight on plant growth, development and disease defense responses. This, in turn, will allow the development of strategies to manage plant disease for life in the space environment.

Plants, plant pathogens, and microgravity--a deadly trio

NASA Technical Reports Server (NTRS)

Leach, J. E.; Ryba-White, M.; Sun, Q.; Wu, C. J.; Hilaire, E.; Gartner, C.; Nedukha, O.; Kordyum, E.; Keck, M.; Leung, H.;

Resistance (R) Genes: Applications and Prospects for Plant Biotechnology and Breeding.

PubMed

Pandolfi, Valesca; Neto, Jose Ribamar Costa Ferreira; da Silva, Manasses Daniel; Amorim, Lidiane Lindinalva Barbosa; Wanderley-Nogueira, Ana Carolina; de Oliveira Silva, Roberta Lane; Kido, Ederson Akio; Crovella, Sergio; Iseppon, Ana Maria Benko

2017-01-01

The discovery of novel plant resistance (R) genes (including their homologs and analogs) opened interesting possibilities for controlling plant diseases caused by several pathogens. However, due to environmental pressure and high selection operated by pathogens, several crop plants have lost specificity, broad-spectrum or durability of resistance. On the other hand, the advances in plant genome sequencing and biotechnological approaches, combined with the increasing knowledge on Rgenes have provided new insights on their applications for plant genetic breeding, allowing the identification and implementation of novel and efficient strategies that enhance or optimize their use for efficiently controlling plant diseases. The present review focuses on main perspectives of application of R-genes and its co-players for the acquisition of resistance to pathogens in cultivated plants, with emphasis on biotechnological inferences, including transgenesis, cisgenesis, directed mutagenesis and gene editing, with examples of success and challenges to be faced. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Rose parental characterization and population development for the identification of novel rose black spot resistance genes [abstract

USDA-ARS?s Scientific Manuscript database

Rose black spot disease, caused by the pathogen Diplocarpon rosae Wolf, is one of the most widespread and serious diseases of outdoor-grown roses worldwide. Defoliation caused by the disease compromises ornamental value, and repeated defoliation events weakens plants and can lead to plant death. Bot...

Irrigation affects severity of root rot caused by Phythophthora plurivora and P. cinnamomi on rhododendron

USDA-ARS?s Scientific Manuscript database

Plant pathogens in the genus Phytophthora cause root rot that decrease product quality and result in plant death and economic losses to the nursery industry. Recently, we found Phytophthora plurivora prevalent on rhododendron in nurseries in the Pacific Northwest, USA, but there is little informatio...

Effectiveness of Natural Antifungal Compounds in Controlling Infection by Grapevine Trunk Disease Pathogens through Pruning Wounds

PubMed Central

Cobos, Rebeca; Mateos, Rosa María; Álvarez-Pérez, José Manuel; Olego, Miguel Angel; Sevillano, Silvia; González-García, Sandra; Garzón-Jimeno, Enrique

2015-01-01

Grapevine trunk fungal pathogens, such as Diplodia seriata and Phaeomoniella chlamydospora, can infect plants through pruning wounds. They cause grapevine trunk diseases and are involved in grapevine decline. Accordingly, the protection of pruning wounds is crucial for the management of grapevine trunk diseases. The efficacy of different natural antifungals in inhibiting the growth of several fungi causing grapevine trunk diseases was evaluated in vitro. The fungi showing greater in vitro efficacy were tested on autoclaved grape wood assays against D. seriata and P. chlamydospora. Based on results from these assays, chitosan oligosaccharide, vanillin, and garlic extract were selected for further evaluation on pruning wounds inoculated with D. seriata and P. chlamydospora in field trials. A significant decrease in plant mortality was observed after 2 years of growth in the plants treated with the different natural antifungals compared to the mortality rate observed in infected plants that were not treated with antifungals. Also, the infection rate for the inoculated pathogens was significantly reduced in plants treated with the selected natural antifungals. Therefore, natural antifungals represent a promising alternative for disease control and could provide significant economic benefits for the grape-growing industry. PMID:26162882

THE USE OF PLANTS TO PROTECT PLANTS AND FOOD AGAINST FUNGAL PATHOGENS: A REVIEW

PubMed Central

Shuping, D.S.S.; Eloff, J.N.

2017-01-01

Background: Plant fungal pathogens play a crucial role in the profitability, quality and quantity of plant production. These phytopathogens are persistent in avoiding plant defences causing diseases and quality losses around the world that amount to billions of US dollars annually. To control the scourge of plant fungal diseases, farmers have used fungicides to manage the damage of plant pathogenic fungi. Drawbacks such as development of resistance and environmental toxicity associated with these chemicals have motivated researchers and cultivators to investigate other possibilities. Materials and Methods: Several databases were accessed to determine work done on protecting plants against plant fungal pathogens with plant extracts using search terms “plant fungal pathogen”, “plant extracts” and “phytopathogens”. Proposals are made on the best extractants and bioassay techniques to be used. Results: In addition to chemical fungicides, biological agents have been used to deal with plant fungal diseases. There are many examples where plant extracts or plant derived compounds have been used as commercial deterrents of fungi on a large scale in agricultural and horticultural setups. One advantage of this approach is that plant extracts usually contain more than one antifungal compound. Consequently the development of resistance of pathogens may be lower if the different compounds affect a different metabolic process. Plants cultivated using plants extracts may also be marketed as organically produced. Many papers have been published on effective antimicrobial compounds present in plant extracts focusing on applications in human health. More research is required to develop suitable, sustainable, effective, cheaper botanical products that can be used to help overcome the scourge of plant fungal diseases. Conclusions: Scientists who have worked only on using plants to control human and animal fungal pathogens should consider the advantages of focusing on plant fungal pathogens. This approach could not only potentially increase food security for rural farmers, lead to commercial rewards, but it is also much easier to test the efficacy in greenhouse or field experiments. Even if extracts are toxic it may still be useful in the floriculture industry. PMID:28638874

The role of effectors and host immunity in plant-necrotrophic fungal interactions.

PubMed

Wang, Xuli; Jiang, Nan; Liu, Jinling; Liu, Wende; Wang, Guo-Liang

2014-01-01

Fungal diseases pose constant threats to the global economy and food safety. As the largest group of plant fungal pathogens, necrotrophic fungi cause heavy crop losses worldwide. The molecular mechanisms of the interaction between necrotrophic fungi and plants are complex and involve sophisticated recognition and signaling networks. Here, we review recent findings on the roles of phytotoxin and proteinaceous effectors, pathogen-associated molecular patterns (PAMPs), and small RNAs from necrotrophic fungi. We also consider the functions of damage-associated molecular patterns (DAMPs), the receptor-like protein kinase BIK1, and epigenetic regulation in plant immunity to necrotrophic fungi.

Multiple Classes of Immune-Related Proteases Associated with the Cell Death Response in Pepper Plants

PubMed Central

Bae, Chungyun; Kim, Su-min; Lee, Dong Ju; Choi, Doil

2013-01-01

Proteases regulate a large number of biological processes in plants, such as metabolism, physiology, growth, and defense. In this study, we carried out virus-induced gene silencing assays with pepper cDNA clones to elucidate the biological roles of protease superfamilies. A total of 153 representative protease genes from pepper cDNA were selected and cloned into a Tobacco rattle virus-ligation independent cloning vector in a loss-of-function study. Silencing of 61 proteases resulted in altered phenotypes, such as the inhibition of shoot growth, abnormal leaf shape, leaf color change, and lethality. Furthermore, the silencing experiments revealed that multiple proteases play a role in cell death and immune response against avirulent and virulent pathogens. Among these 153 proteases, 34 modulated the hypersensitive cell death response caused by infection with an avirulent pathogen, and 16 proteases affected disease symptom development caused by a virulent pathogen. Specifically, we provide experimental evidence for the roles of multiple protease genes in plant development and immune defense following pathogen infection. With these results, we created a broad sketch of each protease function. This information will provide basic information for further understanding the roles of the protease superfamily in plant growth, development, and defense. PMID:23696830

Detailed analysis of metagenome datasets obtained from biogas-producing microbial communities residing in biogas reactors does not indicate the presence of putative pathogenic microorganisms

PubMed Central

2013-01-01

Background In recent years biogas plants in Germany have been supposed to be involved in amplification and dissemination of pathogenic bacteria causing severe infections in humans and animals. In particular, biogas plants are discussed to contribute to the spreading of Escherichia coli infections in humans or chronic botulism in cattle caused by Clostridium botulinum. Metagenome datasets of microbial communities from an agricultural biogas plant as well as from anaerobic lab-scale digesters operating at different temperatures and conditions were analyzed for the presence of putative pathogenic bacteria and virulence determinants by various bioinformatic approaches. Results All datasets featured a low abundance of reads that were taxonomically assigned to the genus Escherichia or further selected genera comprising pathogenic species. Higher numbers of reads were taxonomically assigned to the genus Clostridium. However, only very few sequences were predicted to originate from pathogenic clostridial species. Moreover, mapping of metagenome reads to complete genome sequences of selected pathogenic bacteria revealed that not the pathogenic species itself, but only species that are more or less related to pathogenic ones are present in the fermentation samples analyzed. Likewise, known virulence determinants could hardly be detected. Only a marginal number of reads showed similarity to sequences described in the Microbial Virulence Database MvirDB such as those encoding protein toxins, virulence proteins or antibiotic resistance determinants. Conclusions Findings of this first study of metagenomic sequence reads of biogas producing microbial communities suggest that the risk of dissemination of pathogenic bacteria by application of digestates from biogas fermentations as fertilizers is low, because obtained results do not indicate the presence of putative pathogenic microorganisms in the samples analyzed. PMID:23557021

Paradigms: examples from the bacterium Xylella fastidiosa.

PubMed

Purcell, Alexander

2013-01-01

The history of advances in research on Xylella fastidiosa provides excellent examples of how paradigms both advance and limit our scientific understanding of plant pathogens and the plant diseases they cause. I describe this from a personal perspective, having been directly involved with many persons who made paradigm-changing discoveries, beginning with the discovery that a bacterium, not a virus, causes Pierce's disease of grape and other plant diseases in numerous plant species, including important crop and forest species.

Time-resolved dual transcriptomics reveal early induced Nicotiana benthamiana root genes and conserved infection-promoting Phytophthora palmivora effectors.

PubMed

Evangelisti, Edouard; Gogleva, Anna; Hainaux, Thomas; Doumane, Mehdi; Tulin, Frej; Quan, Clément; Yunusov, Temur; Floch, Kévin; Schornack, Sebastian

2017-05-11

Plant-pathogenic oomycetes are responsible for economically important losses in crops worldwide. Phytophthora palmivora, a tropical relative of the potato late blight pathogen, causes rotting diseases in many tropical crops including papaya, cocoa, oil palm, black pepper, rubber, coconut, durian, mango, cassava and citrus. Transcriptomics have helped to identify repertoires of host-translocated microbial effector proteins which counteract defenses and reprogram the host in support of infection. As such, these studies have helped in understanding how pathogens cause diseases. Despite the importance of P. palmivora diseases, genetic resources to allow for disease resistance breeding and identification of microbial effectors are scarce. We employed the model plant Nicotiana benthamiana to study the P. palmivora root infections at the cellular and molecular levels. Time-resolved dual transcriptomics revealed different pathogen and host transcriptome dynamics. De novo assembly of P. palmivora transcriptome and semi-automated prediction and annotation of the secretome enabled robust identification of conserved infection-promoting effectors. We show that one of them, REX3, suppresses plant secretion processes. In a survey for early transcriptionally activated plant genes we identified a N. benthamiana gene specifically induced at infected root tips that encodes a peptide with danger-associated molecular features. These results constitute a major advance in our understanding of P. palmivora diseases and establish extensive resources for P. palmivora pathogenomics, effector-aided resistance breeding and the generation of induced resistance to Phytophthora root infections. Furthermore, our approach to find infection-relevant secreted genes is transferable to other pathogen-host interactions and not restricted to plants.

[Plant immune system: the basal immunity].

PubMed

Shamraĭ, S N

2014-01-01

Plants have an efficient system of innate immunity which is based on the effective detection of potentially harmful microorganisms and rapid induction of defense responses. The first level of plant immunity is the basal immunity which is induced by the conserved molecular structures of microbes such as bacterial flagellins or fungal chitin, or molecules that result from the interaction of plants with pathogens, for example oligosaccharides and peptides ("danger signals"). Plants recognize these inducers through receptors localized to the plasma membrane, represented mainly receptor-like protein kinases or receptor-like proteins. Activation of the receptor by a ligand triggers a complex network of signaling events which eventually cause an array of plant defense responses to prevent further spread of the pathogen.

Antimicrobial Activity of Seven Essential Oils From Iranian Aromatic Plants Against Common Causes of Oral Infections

PubMed Central

Zomorodian, Kamiar; Ghadiri, Pooria; Saharkhiz, Mohammad Jamal; Moein, Mohammad Reza; Mehriar, Peiman; Bahrani, Farideh; Golzar, Tahereh; Pakshir, Keyvan; Fani, Mohammad Mehdi

2015-01-01

Background: Over the past two decades, there has been a growing trend in using oral hygienic products originating from natural resources such as essential oils (EOs) and plant extracts. Seven aromatic plants used in this study are among popular traditional Iranian medicinal plants with potential application in modern medicine as anti-oral infectious diseases. Objectives: This study was conducted to determine the chemical composition and antimicrobial activities of essential oils from seven medicinal plants against pathogens causing oral infections. Materials and Methods: The chemical compositions of EOs distilled from seven plants were analyzed by gas chromatography/mass spectrometry (GC/MS). These plants included Satureja khuzestanica, S. bachtiarica, Ocimum sanctum, Artemisia sieberi, Zataria multiflora, Carum copticum and Oliveria decumbens. The antimicrobial activity of the essential oils was evaluated by broth micro-dilution in 96 well plates as recommended by the Clinical and Laboratory Standards Institute (CLSI) methods. Results: The tested EOs inhibited the growth of examined oral pathogens at concentrations of 0.015-16 µL/mL. Among the examined oral pathogens, Enterococcus faecalis had the highest Minimum Inhibitory Concentrations (MICs) and Minimum Microbicidal Concentrations (MMCs). Of the examined EOs, S. khuzestanica, Z. multiflora and S. bachtiarica, showed the highest antimicrobial activities, respectively, while Artemisia sieberi exhibited the lowest antimicrobial activity. Conclusions: The excellent antimicrobial activities of the tested EOs might be due to their major phenolic or alcoholic monoterpenes with known antimicrobial activities. Hence, these EOs can be possibly used as an antimicrobial agent in treatment and control of oral pathogens. PMID:25793100

Survival of pathogenic Escherichia coli on basil, lettuce, and spinach

USDA-ARS?s Scientific Manuscript database

The contamination of lettuce, spinach and basil with pathogenic E. coli has caused numerous illnesses over the past decade. E. coli O157:H7, E. coli O104:H4 and avian pathogenic E. coli (APECstx- and APECstx+) were inoculated on basil plants and in promix soiless substrate using drip and overhead ir...

Infection processes of xylem-colonizing pathogenic bacteria: possible explanations for the scarcity of qualitative disease resistance genes against them in crops.

PubMed

Bae, Chungyun; Han, Sang Wook; Song, Yu-Rim; Kim, Bo-Young; Lee, Hyung-Jin; Lee, Je-Min; Yeam, Inhwa; Heu, Sunggi; Oh, Chang-Sik

2015-07-01

Disease resistance against xylem-colonizing pathogenic bacteria in crops. Plant pathogenic bacteria cause destructive diseases in many commercially important crops. Among these bacteria, eight pathogens, Ralstonia solanacearum, Xanthomonas oryzae pv. oryzae, X. campestris pv. campestris, Erwinia amylovora, Pantoea stewartii subsp. stewartii, Clavibacter michiganensis subsp. michiganensis, Pseudomonas syringae pv. actinidiae, and Xylella fastidiosa, infect their host plants through different infection sites and paths and eventually colonize the xylem tissues of their host plants, resulting in wilting symptoms by blocking water flow or necrosis of xylem tissues. Noticeably, only a relatively small number of resistant cultivars in major crops against these vascular bacterial pathogens except X. oryzae pv. oryzae have been found or generated so far, although these pathogens threaten productivity of major crops. In this review, we summarize the lifestyles of major xylem-colonizing bacterial pathogens and then discuss the progress of current research on disease resistance controlled by qualitative disease resistance genes or quantitative trait loci against them. Finally, we propose infection processes of xylem-colonizing bacterial pathogens as one of possible reasons for why so few qualitative disease resistance genes against these pathogens have been developed or identified so far in crops.

Comparative genomic analysis of multiple strains of two unusual plant pathogens: Pseudomonas corrugata and Pseudomonas mediterranea

PubMed Central

Trantas, Emmanouil A.; Licciardello, Grazia; Almeida, Nalvo F.; Witek, Kamil; Strano, Cinzia P.; Duxbury, Zane; Ververidis, Filippos; Goumas, Dimitrios E.; Jones, Jonathan D. G.; Guttman, David S.; Catara, Vittoria; Sarris, Panagiotis F.

2015-01-01

The non-fluorescent pseudomonads, Pseudomonas corrugata (Pcor) and P. mediterranea (Pmed), are closely related species that cause pith necrosis, a disease of tomato that causes severe crop losses. However, they also show strong antagonistic effects against economically important pathogens, demonstrating their potential for utilization as biological control agents. In addition, their metabolic versatility makes them attractive for the production of commercial biomolecules and bioremediation. An extensive comparative genomics study is required to dissect the mechanisms that Pcor and Pmed employ to cause disease, prevent disease caused by other pathogens, and to mine their genomes for genes that encode proteins involved in commercially important chemical pathways. Here, we present the draft genomes of nine Pcor and Pmed strains from different geographical locations. This analysis covered significant genetic heterogeneity and allowed in-depth genomic comparison. All examined strains were able to trigger symptoms in tomato plants but not all induced a hypersensitive-like response in Nicotiana benthamiana. Genome-mining revealed the absence of type III secretion system and known type III effector-encoding genes from all examined Pcor and Pmed strains. The lack of a type III secretion system appears to be unique among the plant pathogenic pseudomonads. Several gene clusters coding for type VI secretion system were detected in all genomes. Genome-mining also revealed the presence of gene clusters for biosynthesis of siderophores, polyketides, non-ribosomal peptides, and hydrogen cyanide. A highly conserved quorum sensing system was detected in all strains, although species specific differences were observed. Our study provides the basis for in-depth investigations regarding the molecular mechanisms underlying virulence strategies in the battle between plants and microbes. PMID:26300874

Two distinct secretion systems facilitate tissue invasion by the rice blast fungus Magnaporthe oryzae

PubMed Central

Giraldo, Martha C.; Dagdas, Yasin F.; Gupta, Yogesh K.; Mentlak, Thomas A.; Yi, Mihwa; Martinez-Rocha, Ana Lilia; Saitoh, Hiromasa; Terauchi, Ryohei; Talbot, Nicholas J.; Valent, Barbara

2013-01-01

To cause plant diseases, pathogenic micro-organisms secrete effector proteins into host tissue to suppress immunity and support pathogen growth. Bacterial pathogens have evolved several distinct secretion systems to target effector proteins, but whether fungi, which cause the major diseases of most crop species, also require different secretory mechanisms is not known. Here we report that the rice blast fungus Magnaporthe oryzae possesses two distinct secretion systems to target effectors during plant infection. Cytoplasmic effectors, which are delivered into host cells, preferentially accumulate in the biotrophic interfacial complex, a novel plant membrane-rich structure associated with invasive hyphae. We show that the biotrophic interfacial complex is associated with a novel form of secretion involving exocyst components and the Sso1 t-SNARE. By contrast, effectors that are secreted from invasive hyphae into the extracellular compartment follow the conventional secretory pathway. We conclude that the blast fungus has evolved distinct secretion systems to facilitate tissue invasion. PMID:23774898

Fabrication of biomimetically-patterned surfaces and their application to probing plant-bacteria interactions

USDA-ARS?s Scientific Manuscript database

Understanding of plant-bacterial interactions is of critical importance for developing effective control measures against infectious diseases caused by foodborne human pathogens. However, limitations of existing scientific tools to access and evaluate natural plant tissues, and the large variations ...

Salmonella interactions with plants and their associated microbiota

USDA-ARS?s Scientific Manuscript database

The increase in the incidence of gastroenteritis outbreaks linked to the consumption of foods of plant origin has ignited public concern and scientific interest in understanding interactions of human enteric pathogens with plants. Enteric disease caused by non-typhoidal Salmonella is a major public ...

Fertilizer N application rate impacts plant-soil feedback in a sanqi production system.

PubMed

Wei, Wei; Yang, Min; Liu, Yixiang; Huang, Huichuan; Ye, Chen; Zheng, Jianfen; Guo, Cunwu; Hao, Minwen; He, Xiahong; Zhu, Shusheng

2018-08-15

Replant failure caused by negative plant-soil feedback (NPFS) in agricultural ecosystems is a critical factor restricting the development of sustainable agriculture. Soil nutrient availability has the capacity to affect plant-soil feedback. Here, we used sanqi (Panax notoginseng), which is severely threatened by NPSF, as a model plant to decipher the overall effects of nitrogen (N) rates on NPSF and the underlying mechanism. We found that a high rate of N at 450kgNha -1 (450N) aggravated the NPSF through the accumulation of pathogens in the soil compared with the optimal 250N. The increased N rates resulted in a significant increase in the soil electrical conductivity and available nitrogen but a decrease in the soil pH and C/N ratio. GeoChip 5.0 data demonstrated that these changed soil properties caused the soil to undergo stress (acidification, salinization and carbon starvation), as indicated by the enriched soil microbial gene abundances related to stress response and nutrition cycling (N, C and S). Accordingly, increased N rates reduced the richness and diversity of soil fungi and bacteria and eventually caused a shift in soil microbes from a bacterial-dominant community to a fungal-dominant community. In particular, the high 450N treatment significantly suppressed the abundance of copiotrophic bacteria, including beneficial genera Bacillus and Pseudomonas, thus weakening the antagonistic activity of these bacteria against fungal pathogens. Moreover, 450N application significantly enriched the abundance of pathogen pathogenicity-related genes. Once sanqi plants were grown in this N-stressed soil, their host-specific fungal pathogen Fusarium oxysporum significantly accumulated, which aggravated the process of NPSF. This study suggested that over-application of nitrogen is not beneficial for disease management or the reduction of fungicide application in agricultural production. Copyright © 2018 Elsevier B.V. All rights reserved.

CRN13 candidate effectors from plant and animal eukaryotic pathogens are DNA-binding proteins which trigger host DNA damage response.

PubMed

Ramirez-Garcés, Diana; Camborde, Laurent; Pel, Michiel J C; Jauneau, Alain; Martinez, Yves; Néant, Isabelle; Leclerc, Catherine; Moreau, Marc; Dumas, Bernard; Gaulin, Elodie

2016-04-01

To successfully colonize their host, pathogens produce effectors that can interfere with host cellular processes. Here we investigated the function of CRN13 candidate effectors produced by plant pathogenic oomycetes and detected in the genome of the amphibian pathogenic chytrid fungus Batrachochytrium dendrobatidis (BdCRN13). When expressed in Nicotiana, AeCRN13, from the legume root pathogen Aphanomyces euteiches, increases the susceptibility of the leaves to the oomycete Phytophthora capsici. When transiently expressed in amphibians or plant cells, AeCRN13 and BdCRN13 localize to the cell nuclei, triggering aberrant cell development and eventually causing cell death. Using Förster resonance energy transfer experiments in plant cells, we showed that both CRN13s interact with nuclear DNA and trigger plant DNA damage response (DDR). Mutating key amino acid residues in a predicted HNH-like endonuclease motif abolished the interaction of AeCRN13 with DNA, the induction of DDR and the enhancement of Nicotiana susceptibility to P. capsici. Finally, H2AX phosphorylation, a marker of DNA damage, and enhanced expression of genes involved in the DDR were observed in A. euteiches-infected Medicago truncatula roots. These results show that CRN13 from plant and animal eukaryotic pathogens promotes host susceptibility by targeting nuclear DNA and inducing DDR. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

Climate change accelerates local disease extinction rates in a long-term wild host-pathogen association.

PubMed

Zhan, Jiasui; Ericson, Lars; Burdon, Jeremy J

2018-02-27

Pathogens are a significant component of all plant communities. In recent years, the potential for existing and emerging pathogens of agricultural crops to cause increased yield losses as a consequence of changing climatic patterns has raised considerable concern. In contrast, the response of naturally occurring, endemic pathogens to a warming climate has received little attention. Here, we report on the impact of a signature variable of global climate change - increasing temperature - on the long-term epidemiology of a natural host-pathogen association involving the rust pathogen Triphragmium ulmariae and its host plant Filipendula ulmaria. In a host-pathogen metapopulation involving approximately 230 host populations growing on an archipelago of islands in the Gulf of Bothnia we assessed changes in host population size and pathogen epidemiological measures over a 25-year period. We show how the incidence of disease and its severity declines over that period and most importantly demonstrate a positive association between a long-term trend of increasing extinction rates in individual pathogen populations of the metapopulation and increasing temperature. Our results are highly suggestive that changing climatic patterns, particularly mean monthly growing season (April-November) temperature, are markedly influencing the epidemiology of plant disease in this host-pathogen association. Given the important role plant pathogens have in shaping the structure of communities, changes in the epidemiology of pathogens have potentially far-reaching impacts on ecological and evolutionary processes. For these reasons, it is essential to increase understanding of pathogen epidemiology, its response to warming, and to invoke these responses in forecasts for the future. © 2018 John Wiley & Sons Ltd.

The influence of bacteria on multitrophic interactions among plants, psyllids, and pathogen.

PubMed

Tamborindeguy, Cecilia; Huot, Ordom Brian; Ibanez, Freddy; Levy, Julien

2017-12-01

The recent emergence of several plant diseases caused by psyllid-borne bacterial pathogens worldwide (Candidatus Liberibacter spp.) has created renewed interest on the interaction between psyllids and bacteria. In spite of these efforts to understand psyllid association with bacteria, many aspects of their interactions remain poorly understood. As more organisms are studied, subtleties on the molecular interactions as well as on the effects of the bacteria on the psyllid host are being uncovered. Additionally, psyllid-borne bacterial phytopathogens can also affect the host plant, which in turn can impact psyllid physiology and behavior. Here, we review the current literature on different aspects of the influence of bacteria on multitrophic interactions among plants, psyllids, and pathogens. We then highlight gaps that need to be addressed to advance this field, which can have significant implications for controlling these newly emergent and other plant diseases. © 2017 Institute of Zoology, Chinese Academy of Sciences.

Virulence Factors of Geminivirus Interact with MYC2 to Subvert Plant Resistance and Promote Vector Performance[C][W

PubMed Central

Li, Ran; Weldegergis, Berhane T.; Li, Jie; Jung, Choonkyun; Qu, Jing; Sun, Yanwei; Qian, Hongmei; Tee, ChuanSia; van Loon, Joop J.A.; Dicke, Marcel; Chua, Nam-Hai; Liu, Shu-Sheng

2014-01-01

A pathogen may cause infected plants to promote the performance of its transmitting vector, which accelerates the spread of the pathogen. This positive effect of a pathogen on its vector via their shared host plant is termed indirect mutualism. For example, terpene biosynthesis is suppressed in begomovirus-infected plants, leading to reduced plant resistance and enhanced performance of the whiteflies (Bemisia tabaci) that transmit these viruses. Although begomovirus-whitefly mutualism has been known, the underlying mechanism is still elusive. Here, we identified βC1 of Tomato yellow leaf curl China virus, a monopartite begomovirus, as the viral genetic factor that suppresses plant terpene biosynthesis. βC1 directly interacts with the basic helix-loop-helix transcription factor MYC2 to compromise the activation of MYC2-regulated terpene synthase genes, thereby reducing whitefly resistance. MYC2 associates with the bipartite begomoviral protein BV1, suggesting that MYC2 is an evolutionarily conserved target of begomoviruses for the suppression of terpene-based resistance and the promotion of vector performance. Our findings describe how this viral pathogen regulates host plant metabolism to establish mutualism with its insect vector. PMID:25490915

Pseudomonas syringae pv. tomato DC3000: a model pathogen for probing disease susceptibility and hormone signaling in plants.

PubMed

Xin, Xiu-Fang; He, Sheng Yang

2013-01-01

Since the early 1980s, various strains of the gram-negative bacterial pathogen Pseudomonas syringae have been used as models for understanding plant-bacterial interactions. In 1991, a P. syringae pathovar tomato (Pst) strain, DC3000, was reported to infect not only its natural host tomato but also Arabidopsis in the laboratory, a finding that spurred intensive efforts in the subsequent two decades to characterize the molecular mechanisms by which this strain causes disease in plants. Genomic analysis shows that Pst DC3000 carries a large repertoire of potential virulence factors, including proteinaceous effectors that are secreted through the type III secretion system and a polyketide phytotoxin called coronatine, which structurally mimics the plant hormone jasmonate (JA). Study of Pst DC3000 pathogenesis has not only provided several conceptual advances in understanding how a bacterial pathogen employs type III effectors to suppress plant immune responses and promote disease susceptibility but has also facilitated the discovery of the immune function of stomata and key components of JA signaling in plants. The concepts derived from the study of Pst DC3000 pathogenesis may prove useful in understanding pathogenesis mechanisms of other plant pathogens.

Adult trees cause density-dependent mortality in conspecific seedlings by regulating the frequency of pathogenic soil fungi.

PubMed

Liang, Minxia; Liu, Xubing; Gilbert, Gregory S; Zheng, Yi; Luo, Shan; Huang, Fengmin; Yu, Shixiao

2016-12-01

Negative density-dependent seedling mortality has been widely detected in tropical, subtropical and temperate forests, with soil pathogens as a major driver. Here we investigated how host density affects the composition of soil pathogen communities and consequently influences the strength of plant-soil feedbacks. In field censuses of six 1-ha permanent plots, we found that survival was much lower for newly germinated seedlings that were surrounded by more conspecific adults. The relative abundance of pathogenic fungi in soil increased with increasing conspecific tree density for five of nine tree species; more soil pathogens accumulated around roots where adult tree density was higher, and this greater pathogen frequency was associated with lower seedling survival. Our findings show how tree density influences populations of soil pathogens, which creates plant-soil feedbacks that contribute to community-level and population-level compensatory trends in seedling survival. © 2016 John Wiley & Sons Ltd/CNRS.

A nitrogen response pathway regulates virulence in plant pathogenic fungi: role of TOR and the bZIP protein MeaB.

PubMed

López-Berges, Manuel S; Rispail, Nicolas; Prados-Rosales, Rafael C; Di Pietro, Antonio

2010-12-01

Virulence in plant pathogenic fungi is controlled through a variety of cellular pathways in response to the host environment. Nitrogen limitation has been proposed to act as a key signal to trigger the in planta expression of virulence genes. Moreover, a conserved Pathogenicity mitogen activated protein kinase (MAPK) cascade is strictly required for plant infection in a wide range of pathogens. We investigated the relationship between nitrogen signaling and the Pathogenicity MAPK cascade in controlling infectious growth of the vascular wilt fungus Fusarium oxysporum. Several MAPK-activated virulence functions such as invasive growth, vegetative hyphal fusion and host adhesion were strongly repressed in the presence of the preferred nitrogen source ammonium. Repression of these functions by ammonium was abolished by L-Methionine sulfoximine (MSX) or rapamycin, two specific inhibitors of Gln synthetase and the protein kinase TOR (Target Of Rapamycin), respectively, and was dependent on the bZIP protein MeaB. Supplying tomato plants with ammonium rather than nitrate resulted in a significant delay of vascular wilt symptoms caused by the F. oxysporum wild type strain, but not by the ΔmeaB mutant. Ammonium also repressed invasive growth in two other pathogens, the rice blast fungus Magnaporthe oryzae and the wheat head blight pathogen Fusarium graminearum. Our results suggest the presence of a conserved nitrogen-responsive pathway that operates via TOR and MeaB to control infectious growth in plant pathogenic fungi.

Role of RpoS in virulence and stress tolerance of the plant pathogen Erwinia carotovora subsp. carotovora.

PubMed

Andersson, R A; Kõiv, V; Norman-Setterblad, C; Pirhonen, M

1999-12-01

The plant-pathogenic bacterium Erwinia carotovora subsp. carotovora causes plant disease mainly through a number of extracellular plant-cell-wall-degrading enzymes. In this study, the ability of an rpoS mutant of the Er. carotovora subsp. carotovora strain SCC3193 to infect plants and withstand environmental stress was characterized. This mutant was found to be sensitive to osmotic and oxidative stresses in vitro and to be deficient in glycogen accumulation. The production of extracellular enzymes in vitro was similar in the mutant and in the wild-type strains. However, the rpoS mutant caused more severe symptoms than the wild-type strain on tobacco plants and also produced more extracellular enzymes in planta, but did not grow to higher cell density in planta compared to the wild-type strain. When tested on plants with reduced catalase activities, which show higher levels of reactive oxygen species, the rpoS mutant was found to cause lower symptom levels and to have impaired growth. In addition, the mutant was unable to compete with the wild-type strain in planta and in vitro. These results suggest that a functional rpoS gene is needed mainly for survival in a competitive environment and during stress conditions, and not for effective infection of plants.

The role of strigolactones and ethylene in disease caused by Pythium irregulare.

PubMed

Blake, Sara N; Barry, Karen M; Gill, Warwick M; Reid, James B; Foo, Eloise

2016-06-01

Plant hormones play key roles in defence against pathogen attack. Recent work has begun to extend this role to encompass not just the traditional disease/stress hormones, such as ethylene, but also growth-promoting hormones. Strigolactones (SLs) are the most recently defined group of plant hormones with important roles in plant-microbe interactions, as well as aspects of plant growth and development, although the knowledge of their role in plant-pathogen interactions is extremely limited. The oomycete Pythium irregulare is a poorly controlled pathogen of many crops. Previous work has indicated an important role for ethylene in defence against this oomycete. We examined the role of ethylene and SLs in response to this pathogen in pea (Pisum sativum L.) at the molecular and whole-plant levels using a set of well-characterized hormone mutants, including an ethylene-insensitive ein2 mutant and SL-deficient and insensitive mutants. We identified a key role for ethylene signalling in specific cell types that reduces pathogen invasion, extending the work carried out in other species. However, we found no evidence that SL biosynthesis or response influences the interaction of pea with P. irregulare or that synthetic SL influences the growth or hyphal branching of the oomycete in vitro. Future work should seek to extend our understanding of the role of SLs in other plant interactions, including with other fungal, bacterial and viral pathogens, nematodes and insect pests. © 2015 BSPP AND JOHN WILEY & SONS LTD.

Agricultural Bioterrorism: Why It Is A Concern And What We Must Do

DTIC Science & Technology

2003-04-07

that causes smallpox. • Fungus are any of a major group (Fungi) of saprophytic and parasitic lower plants that lack chlorophyll and include molds, rusts ...fever* • Sheep and goat pox* • Swine vesicular disease* • Vesicular stomatitis* Plant Pathogens • Rice blast (Magnaporthe griesea) • Wheat stem rust ...Puccinia graminis) • Wheat smut (Fusarium graminearum) Wheat Pathogens • Wheat dwarf geminivirus • Barley yellow dwarf virus • Pseudomonas fascovaginaei

Resistance to rust fungi in Lolium perenne depends on within-species variation and performance of the host species in grasslands of different plant diversity.

PubMed

Roscher, Christiane; Schumacher, Jens; Foitzik, Oliver; Schulze, Ernst-Detlef

2007-08-01

The hypothesis that plant species diversity and genetic variation of the host species decrease the severity of plant diseases is supported by studies of agricultural systems, but experimental evidence from more complex systems is scarce. In an experiment with grassland communities of varying species richness (1, 2, 4, 8, 16, and 60 species) and functional group richness (1, 2, 3, and 4 functional groups), we used different cultivars of Lolium perenne (perennial ryegrass) to study effects of biodiversity and cultivar identity on the occurrence and severity of foliar fungal diseases caused by Puccinia coronata (crown rust) and P. graminis (stem rust). Cultivar monocultures of perennial ryegrass revealed strong differences in pathogen susceptibility among these cultivars. Disease intensity caused by both rust fungi decreased significantly with growing species richness of species mixtures. The response to the diversity gradient was related to the decreased density and size of the host individuals with increasing species richness. The occurrence of other grass species known to be possible hosts of the pathogens in the experimental mixtures did not promote disease intensity in L. perenne, indicating that there was a high host specificity of pathogen strains. Differences in pathogen susceptibility among perennial ryegrass cultivars persisted independent of diversity treatment, host density and host individual size, but resulted in a cultivar-specific pattern of changes in pathogen infestation across the species-richness gradient. Our study provided evidence that within-species variation in pathogen susceptibility and competitive interactions of the host species with the environment, as caused by species diversity treatments, are key determinants of the occurrence and severity of fungal diseases.

First Report of Neofusicoccum ribis causing postharvest decay of apple fruit from cold storage in Pennsylvania

USDA-ARS?s Scientific Manuscript database

Neofusicoccum ribis (Slippers, Crous & M.J. Wingf.), previously known as Botryosphaeria ribis (Grossenb. & Duggar), is an aggressive fungal plant pathogen that is part of the N. ribis/N. parvum species complex that causes stem cankers on a variety of woody plant species. An isolate of N. ribis was ...

The Biology and Biological Activity of Pseudomonas syringae pv. tagetis

USDA-ARS?s Scientific Manuscript database

Pseudomonas syringae pv. tagetis (Pst) is a disease of plants in the family Asteraceae. A distinctive characteristic of this bacterial pathogen is the symptom of apical chlorosis in infected plants, caused by the phytotoxin tagetitoxin. Strains of Pst have been isolated from several plant species ...

Salmonella Persistence in Tomatoes Requires a Distinct Set of Metabolic Functions Identified by Transposon Insertion Sequencing.

PubMed

de Moraes, Marcos H; Desai, Prerak; Porwollik, Steffen; Canals, Rocio; Perez, Daniel R; Chu, Weiping; McClelland, Michael; Teplitski, Max

2017-03-01

Human enteric pathogens, such as Salmonella spp. and verotoxigenic Escherichia coli , are increasingly recognized as causes of gastroenteritis outbreaks associated with the consumption of fruits and vegetables. Persistence in plants represents an important part of the life cycle of these pathogens. The identification of the full complement of Salmonella genes involved in the colonization of the model plant (tomato) was carried out using transposon insertion sequencing analysis. With this approach, 230,000 transposon insertions were screened in tomato pericarps to identify loci with reduction in fitness, followed by validation of the screen results using competition assays of the isogenic mutants against the wild type. A comparison with studies in animals revealed a distinct plant-associated set of genes, which only partially overlaps with the genes required to elicit disease in animals. De novo biosynthesis of amino acids was critical to persistence within tomatoes, while amino acid scavenging was prevalent in animal infections. Fitness reduction of the Salmonella amino acid synthesis mutants was generally more severe in the tomato rin mutant, which hyperaccumulates certain amino acids, suggesting that these nutrients remain unavailable to Salmonella spp. within plants. Salmonella lipopolysaccharide (LPS) was required for persistence in both animals and plants, exemplifying some shared pathogenesis-related mechanisms in animal and plant hosts. Similarly to phytopathogens, Salmonella spp. required biosynthesis of amino acids, LPS, and nucleotides to colonize tomatoes. Overall, however, it appears that while Salmonella shares some strategies with phytopathogens and taps into its animal virulence-related functions, colonization of tomatoes represents a distinct strategy, highlighting this pathogen's flexible metabolism. IMPORTANCE Outbreaks of gastroenteritis caused by human pathogens have been increasingly associated with foods of plant origin, with tomatoes being one of the common culprits. Recent studies also suggest that these human pathogens can use plants as alternate hosts as a part of their life cycle. While dual (animal/plant) lifestyles of other members of the Enterobacteriaceae family are well known, the strategies with which Salmonella colonizes plants are only partially understood. Therefore, we undertook a high-throughput characterization of the functions required for Salmonella persistence within tomatoes. The results of this study were compared with what is known about genes required for Salmonella virulence in animals and interactions of plant pathogens with their hosts to determine whether Salmonella repurposes its virulence repertoire inside plants or whether it behaves more as a phytopathogen during plant colonization. Even though Salmonella utilized some of its virulence-related genes in tomatoes, plant colonization required a distinct set of functions. Copyright © 2017 American Society for Microbiology.

Salmonella Persistence in Tomatoes Requires a Distinct Set of Metabolic Functions Identified by Transposon Insertion Sequencing

PubMed Central

Desai, Prerak; Porwollik, Steffen; Canals, Rocio; Perez, Daniel R.; Chu, Weiping; McClelland, Michael; Teplitski, Max

2016-01-01

ABSTRACT Human enteric pathogens, such as Salmonella spp. and verotoxigenic Escherichia coli, are increasingly recognized as causes of gastroenteritis outbreaks associated with the consumption of fruits and vegetables. Persistence in plants represents an important part of the life cycle of these pathogens. The identification of the full complement of Salmonella genes involved in the colonization of the model plant (tomato) was carried out using transposon insertion sequencing analysis. With this approach, 230,000 transposon insertions were screened in tomato pericarps to identify loci with reduction in fitness, followed by validation of the screen results using competition assays of the isogenic mutants against the wild type. A comparison with studies in animals revealed a distinct plant-associated set of genes, which only partially overlaps with the genes required to elicit disease in animals. De novo biosynthesis of amino acids was critical to persistence within tomatoes, while amino acid scavenging was prevalent in animal infections. Fitness reduction of the Salmonella amino acid synthesis mutants was generally more severe in the tomato rin mutant, which hyperaccumulates certain amino acids, suggesting that these nutrients remain unavailable to Salmonella spp. within plants. Salmonella lipopolysaccharide (LPS) was required for persistence in both animals and plants, exemplifying some shared pathogenesis-related mechanisms in animal and plant hosts. Similarly to phytopathogens, Salmonella spp. required biosynthesis of amino acids, LPS, and nucleotides to colonize tomatoes. Overall, however, it appears that while Salmonella shares some strategies with phytopathogens and taps into its animal virulence-related functions, colonization of tomatoes represents a distinct strategy, highlighting this pathogen's flexible metabolism. IMPORTANCE Outbreaks of gastroenteritis caused by human pathogens have been increasingly associated with foods of plant origin, with tomatoes being one of the common culprits. Recent studies also suggest that these human pathogens can use plants as alternate hosts as a part of their life cycle. While dual (animal/plant) lifestyles of other members of the Enterobacteriaceae family are well known, the strategies with which Salmonella colonizes plants are only partially understood. Therefore, we undertook a high-throughput characterization of the functions required for Salmonella persistence within tomatoes. The results of this study were compared with what is known about genes required for Salmonella virulence in animals and interactions of plant pathogens with their hosts to determine whether Salmonella repurposes its virulence repertoire inside plants or whether it behaves more as a phytopathogen during plant colonization. Even though Salmonella utilized some of its virulence-related genes in tomatoes, plant colonization required a distinct set of functions. PMID:28039131

The coronafacoyl phytotoxins: structure, biosynthesis, regulation and biological activities.

PubMed

Bignell, Dawn R D; Cheng, Zhenlong; Bown, Luke

2018-05-01

Phytotoxins are secondary metabolites that contribute to the development and/or severity of diseases caused by various plant pathogenic microorganisms. The coronafacoyl phytotoxins are an important family of plant toxins that are known or suspected to be produced by several phylogenetically distinct plant pathogenic bacteria, including the gammaproteobacterium Pseudomonas syringae and the actinobacterium Streptomyces scabies. At least seven different family members have been identified, of which coronatine was the first to be described and is the best-characterized. Though nonessential for disease development, coronafacoyl phytotoxins appear to enhance the severity of disease symptoms induced by pathogenic microbes during host infection. In addition, the identification of coronafacoyl phytotoxin biosynthetic genes in organisms not known to be plant pathogens suggests that these metabolites may have additional roles other than as virulence factors. This review focuses on our current understanding of the structures, biosynthesis, regulation, biological activities and evolution of coronafacoyl phytotoxins as well as the different methods that are used to detect these metabolites and the organisms that produce them.

Fungal model systems and the elucidation of pathogenicity determinants

PubMed Central

Perez-Nadales, Elena; Almeida Nogueira, Maria Filomena; Baldin, Clara; Castanheira, Sónia; El Ghalid, Mennat; Grund, Elisabeth; Lengeler, Klaus; Marchegiani, Elisabetta; Mehrotra, Pankaj Vinod; Moretti, Marino; Naik, Vikram; Oses-Ruiz, Miriam; Oskarsson, Therese; Schäfer, Katja; Wasserstrom, Lisa; Brakhage, Axel A.; Gow, Neil A.R.; Kahmann, Regine; Lebrun, Marc-Henri; Perez-Martin, José; Di Pietro, Antonio; Talbot, Nicholas J.; Toquin, Valerie; Walther, Andrea; Wendland, Jürgen

2014-01-01

Fungi have the capacity to cause devastating diseases of both plants and animals, causing significant harvest losses that threaten food security and human mycoses with high mortality rates. As a consequence, there is a critical need to promote development of new antifungal drugs, which requires a comprehensive molecular knowledge of fungal pathogenesis. In this review, we critically evaluate current knowledge of seven fungal organisms used as major research models for fungal pathogenesis. These include pathogens of both animals and plants; Ashbya gossypii, Aspergillus fumigatus, Candida albicans, Fusarium oxysporum, Magnaporthe oryzae, Ustilago maydis and Zymoseptoria tritici. We present key insights into the virulence mechanisms deployed by each species and a comparative overview of key insights obtained from genomic analysis. We then consider current trends and future challenges associated with the study of fungal pathogenicity. PMID:25011008

Species-level correlates of susceptibility to the pathogenic amphibian fungus Batrachochytrium dendrobatidis in the United States

Treesearch

Betsy A. Bancroft; Barbara A. Han; Catherine L. Searle; Lindsay M. Biga; Deanna H. Olson; Lee B. Kats; Joshua J. Lawler; Andrew R. Blaustein

2011-01-01

Disease is often implicated as a factor in population declines of wildlife and plants. Understanding the characteristics that may predispose a species to infection by a particular pathogen can help direct conservation efforts. Recent declines in amphibian populations world-wide are a major conservation issue and may be caused in part by a fungal pathogen, ...

Rhizosphere pseudomonads as probiotics improving plant health.

PubMed

Kim, Young Cheol; Anderson, Anne J

2018-04-20

Many root-colonizing microbes are multifaceted in traits that improve plant health. Although isolates designated as biological control agents directly reduce pathogen growth, many exert additional beneficial features that parallel changes induced in animal and other hosts by health-promoting microbes termed probiotics. Both animal and plant probiotics cause direct antagonism of pathogens and induce systemic immunity in the host to pathogens and other stresses. They also alter host development, and improve host nutrition. The probiotic root-colonizing pseudomonads are generalists in terms of plant hosts, soil habitats and the array of stress responses that are ameliorated in the plant. This review illustrates how the probiotic pseudomonads, nurtured by the C and N sources released by the plant in root exudates, form protective biofilms on the root surface and produce the metabolites or enzymes to boost plant health. The findings reveal the multifunctional nature of many of the microbial metabolites in the plant-probiotic interplay. The beneficial effects of probiotics on plant function can contribute to sustainable yield and quality in agricultural production. This article is protected by copyright. All rights reserved. © 2018 BSPP and John Wiley & Sons Ltd.

Synergisms between microbial pathogens in plant disease complexes: a growing trend

PubMed Central

Lamichhane, Jay Ram; Venturi, Vittorio

2015-01-01

Plant diseases are often thought to be caused by one species or even by a specific strain. Microbes in nature, however, mostly occur as part of complex communities and this has been noted since the time of van Leeuwenhoek. Interestingly, most laboratory studies focus on single microbial strains grown in pure culture; we were therefore unaware of possible interspecies and/or inter-kingdom interactions of pathogenic microbes in the wild. In human and animal infections, it is now being recognized that many diseases are the result of multispecies synergistic interactions. This increases the complexity of the disease and has to be taken into consideration in the development of more effective control measures. On the other hand, there are only a few reports of synergistic pathogen–pathogen interactions in plant diseases and the mechanisms of interactions are currently unknown. Here we review some of these reports of synergism between different plant pathogens and their possible implications in crop health. Finally, we briefly highlight the recent technological advances in diagnostics as these are beginning to provide important insights into the microbial communities associated with complex plant diseases. These examples of synergistic interactions of plant pathogens that lead to disease complexes might prove to be more common than expected and understanding the underlying mechanisms might have important implications in plant disease epidemiology and management. PMID:26074945

Surveys for Pathogens of Monoecious Hydrilla

DTIC Science & Technology

2014-01-01

scab, which severely reduces the quality of infected fruit (Agrios 2005). Similar diseases affect pears (V. pyrina) and hawthorns (V. inaequalis...are leaf, stem, and fruit pathogens of a variety of plants (Farr et al. 1989). Venturia inaequalis, for example, causes a serious disease of apples...in areas where environmental conditions are cool and moist during the early growing season when trees are beginning to set fruit . The disease causes

Sentinel trees as a tool to forecast invasions of alien plant pathogens.

PubMed

Vettraino, AnnaMaria; Roques, Alain; Yart, Annie; Fan, Jian-ting; Sun, Jiang-hua; Vannini, Andrea

2015-01-01

Recent disease outbreaks caused by alien invasive pathogens into European forests posed a serious threat to forest sustainability with relevant environmental and economic effects. Many of the alien tree pathogens recently introduced into Europe were not previously included on any quarantine lists, thus they were not subject to phytosanitary inspections. The identification and description of alien fungi potentially pathogenic to native European flora before their introduction in Europe, is a paramount need in order to limit the risk of invasion and the impact to forest ecosystems. To determine the potential invasive fungi, a sentinel trees plot was established in Fuyang, China, using healthy seedlings of European tree species including Quercus petreae, Q. suber, and Q. ilex. The fungal assemblage associated with symptomatic specimens was studied using the tag-encoded 454 pyrosequencing of the nuclear ribosomal internal transcribed spacer-1 (ITS 1). Taxa with probable Asiatic origin were identified and included plant pathogenic genera. These results indicate that sentinel plants may be a strategic tool to improve the prevention of bioinvasions.

Effect of chitinase on resistance to fungal pathogens in sea buckthorn, Hippophae rhamnoides, and cloning of Class I and III chitinase genes.

PubMed

Sun, Yan-Lin; Hong, Soon-Kwan

2012-08-01

Sea buckthorn (Hippophae rhamnoides L.) is naturally distributed from Asia to Europe. It has been widely planted as an ornamental shrub and is rich in nutritional and medicinal compounds. Fungal pathogens that cause diseases such as dried-shrink disease are threats to the production of this plant. In this study, we isolated the dried-shrink disease pathogen from bark and total chitinase protein from leaves of infected plants. The results of the Oxford Cup experiment suggested that chitinase protein inhibited the growth of this pathogen. To improve pathogen resistance, we cloned chitinase Class I and III genes in H. rhamnoides, designated Hrchi1 and Hrchi3. The full-length cDNA of the open reading frame region of Hrchi1 contained 903 bp encoding 300 amino acids and Hrchi3 contained 894 bp encoding 297 amino acids. Active domain analysis, protein types, and secondary and 3D structures were predicted using online software.

N-acetylcysteine in agriculture, a novel use for an old molecule: focus on controlling the plant-pathogen Xylella fastidiosa.

PubMed

Muranaka, Lígia S; Giorgiano, Thais E; Takita, Marco A; Forim, Moacir R; Silva, Luis F C; Coletta-Filho, Helvécio D; Machado, Marcos A; de Souza, Alessandra A

2013-01-01

Xylella fastidiosa is a plant pathogen bacterium that causes diseases in many different crops. In citrus, it causes Citrus Variegated Chlorosis (CVC). The mechanism of pathogenicity of this bacterium is associated with its capacity to colonize and form a biofilm in the xylem vessels of host plants, and there is not yet any method to directly reduce populations of this pathogen in the field. In this study, we investigated the inhibitory effect of N-Acetylcysteine (NAC), a cysteine analogue used mainly to treat human diseases, on X. fastidiosa in different experimental conditions. Concentrations of NAC over 1 mg/mL reduced bacterial adhesion to glass surfaces, biofilm formation and the amount of exopolysaccharides (EPS). The minimal inhibitory concentration of NAC was 6 mg/mL. NAC was supplied to X. fastidiosa-infected plants in hydroponics, fertigation, and adsorbed to organic fertilizer (NAC-Fertilizer). HPLC analysis indicated that plants absorbed NAC at concentrations of 0.48 and 2.4 mg/mL but not at 6 mg/mL. Sweet orange plants with CVC symptoms treated with NAC (0.48 and 2.4 mg/mL) in hydroponics showed clear symptom remission and reduction in bacterial population, as analyzed by quantitative PCR and bacterial isolation. Experiments using fertigation and NAC-Fertilizer were done to simulate a condition closer to that normally is used in the field. For both, significant symptom remission and a reduced bacterial growth rate were observed. Using NAC-Fertilizer the lag for resurgence of symptoms on leaves after interruption of the treatment increased to around eight months. This is the first report of the anti-bacterial effect of NAC against a phytopathogenic bacterium. The results obtained in this work together with the characteristics of this molecule indicate that the use of NAC in agriculture might be a new and sustainable strategy for controlling plant pathogenic bacteria.

Susceptibility of Australian plant species to Phytophthora ramorum

Treesearch

Kylie Ireland; Daniel H& uuml; berli; Bernard Dell; Ian Smith; David Rizzo; Giles Hardy

2010-01-01

Phytophthora ramorum is an invasive plant pathogen causing considerable and widespread damage in nurseries, gardens, and natural woodland ecosystems of the United States and Europe, and is classified as a Category 1 pest in Australia. It is of particular interest to Australian plant biosecurity as, like P. cinnamomi; it has...

New hosts of Myrothecium SPP. In brazil and a preliminary In Vitro assay of fungicides

PubMed Central

Quezado Duval, A.M.; Henz, G.P.; Paz-Lima, M.L.; Medeiros, A.R.; Miranda, B.E.C.; Pfenning, L.H.; Reis, A.

2010-01-01

Myrothecium roridum and M. verrucaria are two plant pathogenic species causing foliar spots in a large number of cultivated plants. This paper aims to study the causal agents of foliar spots in vegetable crops (sweet pepper, tomato, cucumber), ornamental plants (Spathiphyllum, Solidago canadensis, Anthurium, Dieffenbachia) and a solanaceous weed plant (Nicandra physalodes). Most of the isolates were identified as M. roridum; only the isolate ‘Myr-02’ from S. canadensis was identified as M. verrucaria. All the isolates were pathogenic to their original plant hosts and also to some other plants. Some fungicides were tested in vitro against an isolate of M. roridum and the mycelial growth recorded after seven days. Fungicides with quartenary ammonium, Tebuconzole and copper were highly effective in inhibiting the mycelial growth of M. roridum. This paper confirms the first record of M. roridum causing leaf spots in sweet pepper, tomato, Spathiphyllum, Anthurium, Dieffenbachia and N. physalodes. We also report M. roridum as causal agent of cucumber fruit rot and also M. verrucaria in tango plants. PMID:24031487

Seed treatments to control seedborne fungal pathogens of vegetable crops.

PubMed

Mancini, Valeria; Romanazzi, Gianfranco

2014-06-01

Vegetable crops are frequently infected by fungal pathogens, which can include seedborne fungi. In such cases, the pathogen is already present within or on the seed surface, and can thus cause seed rot and seedling damping-off. Treatment of vegetable seeds has been shown to prevent plant disease epidemics caused by seedborne fungal pathogens. Furthermore, seed treatments can be useful in reducing the amounts of pesticides required to manage a disease, because effective seed treatments can eliminate the need for foliar application of fungicides later in the season. Although the application of fungicides is almost always effective, their non-target environmental impact and the development of pathogen resistance have led to the search for alternative methods, especially in the past few years. Physical treatments that have already been used in the past and treatments with biopesticides, such as plant extracts, natural compounds and biocontrol agents, have proved to be effective in controlling seedborne pathogens. These have been applied alone or in combination, and they are widely used owing to their broad spectrum in terms of disease control and production yield. In this review, the effectiveness of different seed treatments against the main seedborne pathogens of some important vegetable crops is critically discussed. © 2013 Society of Chemical Industry.

A Novel High-Affinity Sucrose Transporter Is Required for Virulence of the Plant Pathogen Ustilago maydis

PubMed Central

Goos, Sarah; Kämper, Jörg; Sauer, Norbert

2010-01-01

Plant pathogenic fungi cause massive yield losses and affect both quality and safety of food and feed produced from infected plants. The main objective of plant pathogenic fungi is to get access to the organic carbon sources of their carbon-autotrophic hosts. However, the chemical nature of the carbon source(s) and the mode of uptake are largely unknown. Here, we present a novel, plasma membrane-localized sucrose transporter (Srt1) from the corn smut fungus Ustilago maydis and its characterization as a fungal virulence factor. Srt1 has an unusually high substrate affinity, is absolutely sucrose specific, and allows the direct utilization of sucrose at the plant/fungal interface without extracellular hydrolysis and, thus, without the production of extracellular monosaccharides known to elicit plant immune responses. srt1 is expressed exclusively during infection, and its deletion strongly reduces fungal virulence. This emphasizes the central role of this protein both for efficient carbon supply and for avoidance of apoplastic signals potentially recognized by the host. PMID:20161717

Proteomics of Plant Pathogenic Fungi

PubMed Central

González-Fernández, Raquel; Prats, Elena; Jorrín-Novo, Jesús V.

2010-01-01

Plant pathogenic fungi cause important yield losses in crops. In order to develop efficient and environmental friendly crop protection strategies, molecular studies of the fungal biological cycle, virulence factors, and interaction with its host are necessary. For that reason, several approaches have been performed using both classical genetic, cell biology, and biochemistry and the modern, holistic, and high-throughput, omic techniques. This work briefly overviews the tools available for studying Plant Pathogenic Fungi and is amply focused on MS-based Proteomics analysis, based on original papers published up to December 2009. At a methodological level, different steps in a proteomic workflow experiment are discussed. Separate sections are devoted to fungal descriptive (intracellular, subcellular, extracellular) and differential expression proteomics and interactomics. From the work published we can conclude that Proteomics, in combination with other techniques, constitutes a powerful tool for providing important information about pathogenicity and virulence factors, thus opening up new possibilities for crop disease diagnosis and crop protection. PMID:20589070

Proteomics of plant pathogenic fungi.

PubMed

González-Fernández, Raquel; Prats, Elena; Jorrín-Novo, Jesús V

2010-01-01

Plant pathogenic fungi cause important yield losses in crops. In order to develop efficient and environmental friendly crop protection strategies, molecular studies of the fungal biological cycle, virulence factors, and interaction with its host are necessary. For that reason, several approaches have been performed using both classical genetic, cell biology, and biochemistry and the modern, holistic, and high-throughput, omic techniques. This work briefly overviews the tools available for studying Plant Pathogenic Fungi and is amply focused on MS-based Proteomics analysis, based on original papers published up to December 2009. At a methodological level, different steps in a proteomic workflow experiment are discussed. Separate sections are devoted to fungal descriptive (intracellular, subcellular, extracellular) and differential expression proteomics and interactomics. From the work published we can conclude that Proteomics, in combination with other techniques, constitutes a powerful tool for providing important information about pathogenicity and virulence factors, thus opening up new possibilities for crop disease diagnosis and crop protection.

Broad and efficient control of major foodborne pathogenic strains of Escherichia coli by mixtures of plant-produced colicins

PubMed Central

Schulz, Steve; Stephan, Anett; Hahn, Simone; Bortesi, Luisa; Jarczowski, Franziska; Bettmann, Ulrike; Paschke, Anne-Katrin; Tusé, Daniel; Stahl, Chad H.; Giritch, Anatoli; Gleba, Yuri

2015-01-01

Enterohemorrhagic Escherichia coli (EHEC) is one of the leading causes of bacterial enteric infections worldwide, causing ∼100,000 illnesses, 3,000 hospitalizations, and 90 deaths annually in the United States alone. These illnesses have been linked to consumption of contaminated animal products and vegetables. Currently, other than thermal inactivation, there are no effective methods to eliminate pathogenic bacteria in food. Colicins are nonantibiotic antimicrobial proteins, produced by E. coli strains that kill or inhibit the growth of other E. coli strains. Several colicins are highly effective against key EHEC strains. Here we demonstrate very high levels of colicin expression (up to 3 g/kg of fresh biomass) in tobacco and edible plants (spinach and leafy beets) at costs that will allow commercialization. Among the colicins examined, plant-expressed colicin M had the broadest antimicrobial activity against EHEC and complemented the potency of other colicins. A mixture of colicin M and colicin E7 showed very high activity against all major EHEC strains, as defined by the US Department of Agriculture/Food and Drug Administration. Treatments with low (less than 10 mg colicins per L) concentrations reduced the pathogenic bacterial load in broth culture by 2 to over 6 logs depending on the strain. In experiments using meats spiked with E. coli O157:H7, colicins efficiently reduced the population of the pathogen by at least 2 logs. Plant-produced colicins could be effectively used for the broad control of pathogenic E. coli in both plant- and animal-based food products and, in the United States, colicins could be approved using the generally recognized as safe (GRAS) regulatory approval pathway. PMID:26351689

Broad and efficient control of major foodborne pathogenic strains of Escherichia coli by mixtures of plant-produced colicins.

PubMed

Schulz, Steve; Stephan, Anett; Hahn, Simone; Bortesi, Luisa; Jarczowski, Franziska; Bettmann, Ulrike; Paschke, Anne-Katrin; Tusé, Daniel; Stahl, Chad H; Giritch, Anatoli; Gleba, Yuri

2015-10-06

Enterohemorrhagic Escherichia coli (EHEC) is one of the leading causes of bacterial enteric infections worldwide, causing ∼100,000 illnesses, 3,000 hospitalizations, and 90 deaths annually in the United States alone. These illnesses have been linked to consumption of contaminated animal products and vegetables. Currently, other than thermal inactivation, there are no effective methods to eliminate pathogenic bacteria in food. Colicins are nonantibiotic antimicrobial proteins, produced by E. coli strains that kill or inhibit the growth of other E. coli strains. Several colicins are highly effective against key EHEC strains. Here we demonstrate very high levels of colicin expression (up to 3 g/kg of fresh biomass) in tobacco and edible plants (spinach and leafy beets) at costs that will allow commercialization. Among the colicins examined, plant-expressed colicin M had the broadest antimicrobial activity against EHEC and complemented the potency of other colicins. A mixture of colicin M and colicin E7 showed very high activity against all major EHEC strains, as defined by the US Department of Agriculture/Food and Drug Administration. Treatments with low (less than 10 mg colicins per L) concentrations reduced the pathogenic bacterial load in broth culture by 2 to over 6 logs depending on the strain. In experiments using meats spiked with E. coli O157:H7, colicins efficiently reduced the population of the pathogen by at least 2 logs. Plant-produced colicins could be effectively used for the broad control of pathogenic E. coli in both plant- and animal-based food products and, in the United States, colicins could be approved using the generally recognized as safe (GRAS) regulatory approval pathway.

The Emerging British Verticillium longisporum Population Consists of Aggressive Brassica Pathogens.

PubMed

Depotter, Jasper R L; Rodriguez-Moreno, Luis; Thomma, Bart P H J; Wood, Thomas A

2017-11-01

Verticillium longisporum is an economically important fungal pathogen of brassicaceous crops that originated from at least three hybridization events between different Verticillium spp., leading to the hybrid lineages A1/D1, A1/D2, and A1/D3. Isolates of lineage A1/D1 generally cause stem striping on oilseed rape (Brassica napus), which has recently been reported for the first time to occur in the United Kingdom. Intriguingly, the emerging U.K. population is distinct from the north-central European stem striping population. Little is known about the pathogenicity of the newly emerged U.K. population; hence, pathogenicity tests were executed to compare British isolates to previously characterized reference strains. In addition to the model plant Arabidopsis thaliana, the pathogenicity of four British isolates was assessed on four cultivars of three Brassica crop species: oilseed rape (Quartz and Incentive), cauliflower (Clapton), and Chinese cabbage (Hilton). To this end, vascular discoloration of the roots, plant biomass accumulations, and fungal stem colonization upon isolate infection were evaluated. The British isolates appeared to be remarkably aggressive, because plant biomass was significantly affected and severe vascular discoloration was observed. The British isolates were successful stem colonizers and the extent of fungal colonization negatively correlated with plant biomass of cauliflower and Quartz oilseed rape. However, in Quartz, the fungal colonization of A1/D1 isolates was significantly lower than that of the virulent reference isolate from lineage A1/D3, PD589. Moreover, despite levels of stem colonization similar to those of A1/D1 strains, PD589 did not cause significant disease on Incentive. Thus, A1/D1 isolates, including British isolates, are aggressive oilseed rape pathogens despite limited colonization levels in comparison with a virulent A1/D3 isolate.

Expression of an Engineered Heterologous Antimicrobial Peptide in Potato Alters Plant Development and Mitigates Normal Abiotic and Biotic Responses

PubMed Central

Goyal, Ravinder K.; Hancock, Robert E. W.; Mattoo, Autar K.; Misra, Santosh

2013-01-01

Antimicrobial cationic peptides (AMPs) are ubiquitous small proteins used by living cells to defend against a wide spectrum of pathogens. Their amphipathic property helps their interaction with negatively charged cellular membrane of the pathogen causing cell lysis and death. AMPs also modulate signaling pathway(s) and cellular processes in animal models; however, little is known of cellular processes other than the pathogen-lysis phenomenon modulated by AMPs in plants. An engineered heterologous AMP, msrA3, expressed in potato was previously shown to cause resistance of the transgenic plants against selected fungal and bacterial pathogens. These lines together with the wild type were studied for growth habits, and for inducible defense responses during challenge with biotic (necrotroph Fusarium solani) and abiotic stressors (dark-induced senescence, wounding and temperature stress). msrA3-expression not only conferred protection against F. solani but also delayed development of floral buds and prolonged vegetative phase. Analysis of select gene transcript profiles showed that the transgenic potato plants were suppressed in the hypersensitive (HR) and reactive oxygen species (ROS) responses to both biotic and abiotic stressors. Also, the transgenic leaves accumulated lesser amounts of the defense hormone jasmonic acid upon wounding with only a slight change in salicylic acid as compared to the wild type. Thus, normal host defense responses to the pathogen and abiotic stressors were mitigated by msrA3 expression suggesting MSRA3 regulates a common step(s) of these response pathways. The stemming of the pathogen growth and mitigating stress response pathways likely contributes to resource reallocation for higher tuber yield. PMID:24147012

Comparative and bioinformatics analyses of pathogenic bacterial secretomes identified by mass spectrometry in Burkholderia species.

PubMed

Nguyen, Thao Thi; Chon, Tae-Soo; Kim, Jaehan; Seo, Young-Su; Heo, Muyoung

2017-07-01

Secreted proteins (secretomes) play crucial roles during bacterial pathogenesis in both plant and human hosts. The identification and characterization of secretomes in the two plant pathogens Burkholderia glumae BGR1 and B. gladioli BSR3, which cause diseases in rice such as seedling blight, panicle blight, and grain rot, are important steps to not only understand the disease-causing mechanisms but also find remedies for the diseases. Here, we identified two datasets of secretomes in B. glumae BGR1 and B. gladioli BSR3, which consist of 118 and 111 proteins, respectively, using mass spectrometry approach and literature curation. Next, we characterized the functional properties, potential secretion pathways and sequence information properties of secretomes of two plant pathogens in a comparative analysis by various computational approaches. The ratio of potential non-classically secreted proteins (NCSPs) to classically secreted proteins (CSPs) in B. glumae BGR1 was greater than that in B. gladioli BSR3. For CSPs, the putative hydrophobic regions (PHRs) which are essential for secretion process of CSPs were screened in detail at their N-terminal sequences using hidden Markov model (HMM)-based method. Total 31 pairs of homologous proteins in two bacterial secretomes were indicated based on the global alignment (identity ≥ 70%). Our results may facilitate the understanding of the species-specific features of secretomes in two plant pathogenic Burkholderia species.

Shoot the Message, Not the Messenger—Combating Pathogenic Virulence in Plants by Inhibiting Quorum Sensing Mediated Signaling Molecules

PubMed Central

Alagarasan, Ganesh; Aswathy, Kumar S.; Madhaiyan, Munusamy

2017-01-01

Immunity, virulence, biofilm formation, and survival in the host environment are regulated by the versatile nature of density dependent microbial cell signaling, also called quorum sensing (QS). The QS molecules can associate with host plant tissues and, at times, cause a change in its gene expression at the downstream level through inter-kingdom cross talking. Progress in controlling QS through fungicide/bactericide in pathogenic microscopic organisms has lead to a rise of antibiotic resistance pathogens. Here, we review the application of selective quorum quenching (QQ) endophytes to control phytopathogens that are shared by most, if not all, terrestrial plant species as well as aquatic plants. Allowing the plants to posses endophytic colonies through biotization will be an additional and a sustainable encompassing methodology resulting in attenuated virulence rather than killing the pathogens. Furthermore, the introduced endophytes could serve as a potential biofertilizer and bioprotection agent, which in turn increases the PAMP- triggered immunity and hormonal systemic acquired resistance (SAR) in plants through SA-JA-ET signaling systems. This paper discusses major challenges imposed by QS and QQ application in biotechnology. PMID:28446917

Direct and Indirect Visualization of Bacterial Effector Delivery into Diverse Plant Cell Types during Infection[OPEN

PubMed Central

Henry, Elizabeth; Jauneau, Alain; Deslandes, Laurent

2017-01-01

To cause disease, diverse pathogens deliver effector proteins into host cells. Pathogen effectors can inhibit defense responses, alter host physiology, and represent important cellular probes to investigate plant biology. However, effector function and localization have primarily been investigated after overexpression in planta. Visualizing effector delivery during infection is challenging due to the plant cell wall, autofluorescence, and low effector abundance. Here, we used a GFP strand system to directly visualize bacterial effectors delivered into plant cells through the type III secretion system. GFP is a beta barrel that can be divided into 11 strands. We generated transgenic Arabidopsis thaliana plants expressing GFP1-10 (strands 1 to 10). Multiple bacterial effectors tagged with the complementary strand 11 epitope retained their biological function in Arabidopsis and tomato (Solanum lycopersicum). Infection of plants expressing GFP1-10 with bacteria delivering GFP11-tagged effectors enabled direct effector detection in planta. We investigated the temporal and spatial delivery of GFP11-tagged effectors during infection with the foliar pathogen Pseudomonas syringae and the vascular pathogen Ralstonia solanacearum. Thus, the GFP strand system can be broadly used to investigate effector biology in planta. PMID:28600390

Temporal and spatial scaling of the genetic structure of a vector-borne plant pathogen.

PubMed

Coletta-Filho, Helvécio D; Francisco, Carolina S; Almeida, Rodrigo P P

2014-02-01

The ecology of plant pathogens of perennial crops is affected by the long-lived nature of their immobile hosts. In addition, changes to the genetic structure of pathogen populations may affect disease epidemiology and management practices; examples include local adaptation of more fit genotypes or introduction of novel genotypes from geographically distant areas via human movement of infected plant material or insect vectors. We studied the genetic structure of Xylella fastidiosa populations causing disease in sweet orange plants in Brazil at multiple scales using fast-evolving molecular markers (simple-sequence DNA repeats). Results show that populations of X. fastidiosa were regionally isolated, and that isolation was maintained for populations analyzed a decade apart from each other. However, despite such geographic isolation, local populations present in year 2000 were largely replaced by novel genotypes in 2009 but not as a result of migration. At a smaller spatial scale (individual trees), results suggest that isolates within plants originated from a shared common ancestor. In summary, new insights on the ecology of this economically important plant pathogen were obtained by sampling populations at different spatial scales and two different time points.

Unravelling Linkages between Plant Community Composition and the Pathogen-Suppressive Potential of Soils

PubMed Central

Latz, Ellen; Eisenhauer, Nico; Rall, Björn Christian; Scheu, Stefan; Jousset, Alexandre

2016-01-01

Plant diseases cause dramatic yield losses worldwide. Current disease control practices can be deleterious for the environment and human health, calling for alternative and sustainable management regimes. Soils harbour microorganisms that can efficiently suppress pathogens. Uncovering mediators driving their functioning in the field still remains challenging, but represents an essential step in order to develop strategies for increased soil health. We set up plant communities of varying richness to experimentally test the potential of soils differing in plant community history to suppress the pathogen Rhizoctonia solani. The results indicate that plant communities shape soil-disease suppression via changes in abiotic soil properties and the abundance of bacterial groups including species of the genera Actinomyces, Bacillus and Pseudomonas. Further, the results suggest that pairwise interactions between specific plant species strongly affect soil suppressiveness. Using structural equation modelling, we provide a pathway orientated framework showing how the complex interactions between plants, soil and microorganisms jointly shape soil suppressiveness. Our results stress the importance of plant community composition as a determinant of soil functioning, such as the disease suppressive potential of soils. PMID:27021053

Antibacterial activity of plant extracts on foodborne bacterial pathogens and food spoilage bacteria

USDA-ARS?s Scientific Manuscript database

Bacterial foodborne diseases are caused by consumption of foods contaminated with bacteria and/or their toxins. In this study, we evaluated antibacterial properties of twelve different extracts including turmeric, lemon and different kinds of teas against four major pathogenic foodborne bacteria inc...

Principles of Plant-Microbe Interactions - Microbes for Sustainable Agriculture

USDA-ARS?s Scientific Manuscript database

Crops lack resistance to many soilborne pathogens and rely on antagonistic microbes recruited from the soil microbiome to protect their roots. Disease-suppressive soils, the best examples of microbial-based defense, are soils in which a pathogen does not establish or persist, establishes but causes ...

Emergence of the sudden oak death pathogen Phytophthora ramorum

Treesearch

Niklaus J. Grunwald; Matteo Garbelotto; Erica M. Goss; Kurt Huengens; Simone Prospero

2012-01-01

The recently emerged plant pathogen Phytophthora ramorum is responsible for causing the sudden oak death epidemic. This review documents the emergence of P. ramorum based on evolutionary and population genetic analyses. Currently infection by P. ramorum occurs only in Europe and North America and three...

Molecular genetics of Erwinia amylovora involved in the development of fire blight.

PubMed

Oh, Chang-Sik; Beer, Steven V

2005-12-15

The bacterial plant pathogen, Erwinia amylovora, causes the devastating disease known as fire blight in some Rosaceous plants like apple, pear, quince, raspberry and several ornamentals. Knowledge of the factors affecting the development of fire blight has mushroomed in the last quarter century. On the molecular level, genes encoding a Hrp type III secretion system, genes encoding enzymes involved in synthesis of extracellular polysaccharides and genes facilitating the growth of E. amylovora in its host plants have been characterized. The Hrp pathogenicity island, delimited by genes suggesting horizontal gene transfer, is composed of four distinct regions, the hrp/hrc region, the HEE (Hrp effectors and elicitors) region, the HAE (Hrp-associated enzymes) region, and the IT (Island transfer) region. The Hrp pathogenicity island encodes a Hrp type III secretion system (TTSS), which delivers several proteins from bacteria to plant apoplasts or cytoplasm. E. amylovora produces two exopolysaccharides, amylovoran and levan, which cause the characteristic fire blight wilting symptom in host plants. In addition, other genes, and their encoded proteins, have been characterized as virulence factors of E. amylovora that encode enzymes facilitating sorbitol metabolism, proteolytic activity and iron harvesting. This review summarizes our understanding of the genes and gene products of E. amylovora that are involved in the development of the fire blight disease.

A Permutation-Randomization Approach to Test the Spatial Distribution of Plant Diseases.

PubMed

Lione, G; Gonthier, P

2016-01-01

The analysis of the spatial distribution of plant diseases requires the availability of trustworthy geostatistical methods. The mean distance tests (MDT) are here proposed as a series of permutation and randomization tests to assess the spatial distribution of plant diseases when the variable of phytopathological interest is categorical. A user-friendly software to perform the tests is provided. Estimates of power and type I error, obtained with Monte Carlo simulations, showed the reliability of the MDT (power > 0.80; type I error < 0.05). A biological validation on the spatial distribution of spores of two fungal pathogens causing root rot on conifers was successfully performed by verifying the consistency between the MDT responses and previously published data. An application of the MDT was carried out to analyze the relation between the plantation density and the distribution of the infection of Gnomoniopsis castanea, an emerging fungal pathogen causing nut rot on sweet chestnut. Trees carrying nuts infected by the pathogen were randomly distributed in areas with different plantation densities, suggesting that the distribution of G. castanea was not related to the plantation density. The MDT could be used to analyze the spatial distribution of plant diseases both in agricultural and natural ecosystems.

Contribution of a harpin protein from Xanthomonas axonopodis pv. citri to pathogen virulence.

PubMed

Sgro, Germán G; Ficarra, Florencia A; Dunger, Germán; Scarpeci, Telma E; Valle, Estela M; Cortadi, Adriana; Orellano, Elena G; Gottig, Natalia; Ottado, Jorgelina

2012-12-01

Xanthomonas axonopodis pv. citri (Xac), the bacterium that causes citrus canker, contains a gene in the hrp [for hypersensitive response (HR) and pathogenicity] cluster that encodes a harpin protein called Hpa1. Hpa1 produced HR in the nonhost plants tobacco, pepper and Arabidopsis, whereas, in the host plant citrus, it elicited a weak defence response with no visible phenotype. Co-infiltrations of Xac with or without the recombinant Hpa1 protein in citrus leaves produced a larger number of cankers in the presence of the protein. To characterize the effect of Hpa1 during the disease, an XacΔhpa1 mutant was constructed, and infiltration of this mutant caused a smaller number of cankers. In addition, the lack of Hpa1 hindered bacterial aggregation both in solution and in planta. Analysis of citrus leaves infiltrated with Hpa1 revealed alterations in mesophyll morphology caused by the presence of cavitations and crystal idioblasts, suggesting the binding of the harpin to plant membranes and the elicitation of signalling cascades. Overall, these results suggest that, even though Hpa1 elicits the defence response in nonhost plants and, to a lesser extent, in host plants, its main roles in citrus canker are to alter leaf mesophyll structure and to aggregate bacterial cells, and thus increase virulence and pathogen fitness. We expressed the N-terminal and C-terminal regions and found that, although both regions elicited HR in nonhost plants, only the N-terminal region showed increased virulence and bacterial aggregation, supporting the role of this region of the protein as the main active domain. © 2012 THE AUTHORS. MOLECULAR PLANT PATHOLOGY © 2012 BSPP AND BLACKWELL PUBLISHING LTD.

Development of qPCR systems to quantify shoot infections by canker-causing pathogens in stone fruits and nut crops.

PubMed

Luo, Y; Gu, S; Felts, D; Puckett, R D; Morgan, D P; Michailides, T J

2017-02-01

To develop real-time PCR assays for quantification of shoot infection levels of canker disease of stone fruits and nut crops caused by six fungal pathogen groups. This study focused on six major canker-causing fungal pathogen groups: Phomopsis sp., Botryosphaeria dothidea, Lasiodiplodia sp., Cytospora sp., Neofusicoccum sp. and Diplodia sp., occurring in stone fruits and nut crops in California. DNA primers were designed to specifically target each of the six pathogen groups after the specificity tests using canker-causing and non-canker-causing pathogens and by using DNA sequences of other species from GenBank using blast. The quantitative real-time PCR (qPCR) systems were developed and used to quantify the infection levels of inoculated dried plum shoots. For Neofusicoccum sp. and Phomopsis sp., which were used in inoculation of walnut shoots, the values of the molecular severity ranged from 5·60 to 6·94 during the 16 days of latent infection period. The qPCR assays were more efficient, accurate and precise to quantify latent infections caused by canker-causing pathogens as compared to the traditional plating methods. This study demonstrated the potential of using the developed qPCR systems for epidemiological studies on canker diseases of woody plants. © 2016 The Society for Applied Microbiology.

Effect of volatile compounds produced by Ralstonia solanacearum on plant growth promoting and systemic resistance inducing potential of Bacillus volatiles.

PubMed

Tahir, Hafiz Abdul Samad; Gu, Qin; Wu, Huijun; Raza, Waseem; Safdar, Asma; Huang, Ziyang; Rajer, Faheem Uddin; Gao, Xuewen

2017-08-02

Microbial volatiles play an expedient role in the agricultural ecological system by enhancing plant growth and inducing systemic resistance against plant pathogens, without causing hazardous effects on the environment. To explore the effects of VOCs of Ralstonia solanacearum TBBS1 (Rs) on tobacco plant growth and on plant growth promoting efficiency of VOCs produced by Bacillus subtilis SYST2, experiments were conducted both in vitro and in planta. The VOCs produced by SYST2 significantly enhanced the plant growth and induced the systemic resistance (ISR) against wilt pathogen Rs in all experiments. The SYST2-VOCs significantly increased PPO and PAL activity and over-expressed the genes relating to expansin, wilt resistance, and plant defense while repressed the genes relating to ethylene production. More interestingly, VOCs produced by pathogen, Rs had no significant effect on plant growth; however, Rs-VOCs decreased the growth promoting potential of SYST2-VOCs when plants were exposed to VOCs produced by both SYST2 and Rs. The co-culture of SYST2 and Rs revealed that they inhibited the growth of each other; however, the inhibition of Rs by SYST2-VOCs appeared to be greater than that of SYST2 by Rs-VOCs. Our findings provide new insights regarding the interaction among SYST2-VOCs, Rs-VOCs and plant, resulting in growth promotion and induced systemic resistance against the bacterial wilt pathogen Rs. This is the first report of the effect of VOCs produced by pathogenic microorganism on plant growth and on plant growth-promoting and systemic resistance-inducing potential of PGPR strain SYST2.

Colonization of cashew plants by Lasiodiplodia theobromae: Microscopical features

USDA-ARS?s Scientific Manuscript database

Lasiodiplodia theobromae is a phytopathogenic fungus causing gummosis, a threatening disease for cashew plants in Brazil. In an attempt to investigate the ultrastructural features of the pathogen colonization and its response to immunofluorescence labeling, light, confocal and electron microscope st...

The role of strigolactones during plant interactions with the pathogenic fungus Fusarium oxysporum.

PubMed

Foo, Eloise; Blake, Sara N; Fisher, Brendan J; Smith, Jason A; Reid, James B

2016-06-01

Strigolactones (SLs) do not influence spore germination or hyphal growth of Fusarium oxysporum. Mutant studies revealed no role for SLs but a role for ethylene signalling in defence against this pathogen in pea. Strigolactones (SLs) play important roles both inside the plant as a hormone and outside the plant as a rhizosphere signal in interactions with mycorrhizal fungi and parasitic weeds. What is less well understood is any potential role SLs may play in interactions with disease causing microbes such as pathogenic fungi. In this paper we investigate the influence of SLs on the hemibiotrophic pathogen Fusarium oxysporum f.sp. pisi both directly via their effects on fungal growth and inside the plant through the use of a mutant deficient in SL. Given that various stereoisomers of synthetic and naturally occuring SLs can display different biological activities, we used (+)-GR24, (-)-GR24 and the naturally occurring SL, (+)-strigol, as well as a racemic mixture of 5-deoxystrigol. As a positive control, we examined the influence of a plant mutant with altered ethylene signalling, ein2, on disease development. We found no evidence that SLs influence spore germination or hyphal growth of Fusarium oxysporum and that, while ethylene signalling influences pea susceptibility to this pathogen, SLs do not.

Gene expression profiling of the plant pathogenic basidiomycetous fungus Rhizoctonia solani AG 4 reveals putative virulence factors

USDA-ARS?s Scientific Manuscript database

Rhizoctonia solani is a ubiquitous basidiomycetous soilborne fungal pathogen causing damping off of seedlings, aerial blights and postharvest diseases. To gain insight into the molecular mechanisms of pathogenesis a global approach based on analysis of expressed sequence tags (ESTs) was undertaken. ...

Virulence and molecular characterization of experimental isolates of the stripe rust pathogen (Puccinia striiformis) indicate somatic recombination

USDA-ARS?s Scientific Manuscript database

Puccinia striiformis causes stripe rust on wheat, barley, and grasses. Natural population studies have indicated that somatic recombination plays a possible role in the pathogen variation. To determine if somatic recombination can occur, susceptible wheat or barley plants were inoculated with mixe...

Plant-derived antimicrobial eugenol modulates C. jejuni proteome and virulence critical for colonization in chickens

USDA-ARS?s Scientific Manuscript database

Campylobacter jejuni is an important foodborne pathogen that causes severe diarrhea in humans. Chickens act as the reservoir host for Campylobacter, wherein the pathogen colonizes the ceca leading to contaminated poultry products during slaughter. The potential of natural intervention strategies, in...

Nitric oxide detoxification by Fusarium verticillioides flavohemoglobin and role in pathogenicity of maize

USDA-ARS?s Scientific Manuscript database

Fusarium verticillioides is a non-obligate plant pathogen of maize causing a number of specific diseases, including root rot, kernel rot, seed rot, stalk rot, and seedling blight. The saprophytic nature of this fungus, its production of the mycotoxin fumonisin, and complex relationship maize puts t...

Adaptation to the Host Environment by Plant-Pathogenic Fungi.

PubMed

van der Does, H Charlotte; Rep, Martijn

2017-08-04

Many fungi can live both saprophytically and as endophyte or pathogen inside a living plant. In both environments, complex organic polymers are used as sources of nutrients. Propagation inside a living host also requires the ability to respond to immune responses of the host. We review current knowledge of how plant-pathogenic fungi do this. First, we look at how fungi change their global gene expression upon recognition of the host environment, leading to secretion of effectors, enzymes, and secondary metabolites; changes in metabolism; and defense against toxic compounds. Second, we look at what is known about the various cues that enable fungi to sense the presence of living plant cells. Finally, we review literature on transcription factors that participate in gene expression in planta or are suspected to be involved in that process because they are required for the ability to cause disease.

Global food and fibre security threatened by current inefficiencies in fungal identification.

PubMed

Crous, Pedro W; Groenewald, Johannes Z; Slippers, Bernard; Wingfield, Michael J

2016-12-05

Fungal pathogens severely impact global food and fibre crop security. Fungal species that cause plant diseases have mostly been recognized based on their morphology. In general, morphological descriptions remain disconnected from crucially important knowledge such as mating types, host specificity, life cycle stages and population structures. The majority of current fungal species descriptions lack even the most basic genetic data that could address at least some of these issues. Such information is essential for accurate fungal identifications, to link critical metadata and to understand the real and potential impact of fungal pathogens on production and natural ecosystems. Because international trade in plant products and introduction of pathogens to new areas is likely to continue, the manner in which fungal pathogens are identified should urgently be reconsidered. The technologies that would provide appropriate information for biosecurity and quarantine already exist, yet the scientific community and the regulatory authorities are slow to embrace them. International agreements are urgently needed to enforce new guidelines for describing plant pathogenic fungi (including key DNA information), to ensure availability of relevant data and to modernize the phytosanitary systems that must deal with the risks relating to trade-associated plant pathogens.This article is part of the themed issue 'Tackling emerging fungal threats to animal health, food security and ecosystem resilience'. © 2016 The Author(s).

Biocontrol mechanism by root-associated Bacillus amyloliquefaciens FZB42 - a review.

PubMed

Chowdhury, Soumitra Paul; Hartmann, Anton; Gao, XueWen; Borriss, Rainer

2015-01-01

Bacillus amyloliquefaciens subsp. plantarum FZB42 is a Gram-positive model bacterium for unraveling plant-microbe interactions in Bacilli. In addition, FZB42 is used commercially as biofertilizer and biocontrol agent in agriculture. Genome analysis of FZB42 revealed that nearly 10% of the FZB42 genome is devoted to synthesizing antimicrobial metabolites and their corresponding immunity genes. However, recent investigations in planta demonstrated that - except surfactin - the amount of such compounds found in vicinity of plant roots is relatively low, making doubtful a direct function in suppressing competing microflora including plant pathogens. These metabolites have been also suspected to induce changes within the rhizosphere microbial community, which might affect environment and plant health. However, sequence analysis of rhizosphere samples revealed only marginal changes in the root microbiome, suggesting that secondary metabolites are not the key factor in protecting plants from pathogenic microorganisms. On the other hand, adding FZB42 to plants compensate, at least in part, changes in the community structure caused by the pathogen, indicating an interesting mechanism of plant protection by beneficial Bacilli. Sub-lethal concentrations of cyclic lipopeptides and volatiles produced by plant-associated Bacilli trigger pathways of induced systemic resistance (ISR), which protect plants against attacks of pathogenic microbes, viruses, and nematodes. Stimulation of ISR by bacterial metabolites is likely the main mechanism responsible for biocontrol action of FZB42.

Fusaric acid is a crucial factor in the disturbance of leaf water imbalance in Fusarium-infected banana plants.

PubMed

Dong, Xian; Ling, Ning; Wang, Min; Shen, Qirong; Guo, Shiwei

2012-11-01

Fusarium wilt of banana is caused by Fusarium oxysporum f. sp. cubense infection. The initial chlorosis symptoms occur progressively from lower to upper leaves, with wilt symptoms subsequently occurring in the whole plant. To determine the effect of the pathogen infection on the gas exchange characteristics and water content in banana leaves, hydroponic experiments with pathogen inoculation were conducted in a greenhouse. Compared with control plants, infected banana seedlings showed a higher leaf temperature as determined by thermal imaging. Reduced stomatal conductance (g(s)) and transpiration rate (E) in infected plants resulted in lower levels of water loss than in control plants. Water potential in heavily diseased plants (II) was significantly reduced and the E/g(s) ratio was higher than in noninfected plants, indicating the occurrence of uncontrolled water loss not regulated by stomata in diseased plants. As no pathogen colonies were detected from the infected plant leaves, the crude toxin was extracted from the pathogen culture and evaluated about the effect on banana plant to further investigate the probable reason of these physiological changes in Fusarium-infected banana leaf. The phytotoxin fusaric acid (FA) was found in the crude toxin, and both crude toxin and pure FA had similar effects as the pathogen infection on the physiological changes in banana leaf. Additionally, FA was present at all positions in diseased plants and its concentration was positively correlated with the incidence of disease symptoms. Taken together, these observations indicated that FA secreted by the pathogen is an important factor involved in the disturbance of leaf temperature, resulting in uncontrolled leaf water loss and electrolyte leakage due to damaging the cell membrane. In conclusion, FA plays a critical role in accelerating the development of Fusarium wilt in banana plants by acting as a phytotoxin. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

WHEAT LEAF RUST SEVERITY AS AFFECTED BY PLANT DENSITY AND SPECIES PROPORTION IN SIMPLE COMMUNITIES OF WHEAT AND WILD OATS

EPA Science Inventory

While it is generally accepted that dense stands of plants exacerbate epidemics caused by foliar pathogens, there is little experimental evidence to support this view. We grew model plant communities consisting of wheat and wild oats at different densities and proportions and exp...

WHEAT LEAF RUST SEVERITY AS AFFECTED BY PLANT DENSITY AND SPECIES PROPORTION IN SIMPLE COMMUNITIES OF WHEAT AND WILD OATS

EPA Science Inventory

While it is generally accepted that dense stands of plants exacerbate epidermics caused by foliar pathogens, there is little experimental evidence to support this view. We grew model plant communities consisting of wheat and wild oats at different densities and proportions and ex...

Clavibacter michiganensis subsp. michiganensis: first steps in the understanding of virulence of a Gram-positive phytopathogenic bacterium.

PubMed

Gartemann, Karl-Heinz; Kirchner, Oliver; Engemann, Jutta; Gräfen, Ines; Eichenlaub, Rudolf; Burger, Annette

2003-12-19

Clavibacter michiganensis subsp. michiganensis is a plant-pathogenic actinomycete. It infects tomato, spreads through the xylem and causes bacterial wilt and canker. The wild-type strain NCPPB382 carries two plasmids, pCM1 and pCM2. The cured plasmid-free derivative CMM100 is still able to colonize tomato, but no disease symptoms develop indicating that all genes required for successful infection, establishment and growth in the plant reside on the chromosome. Both plasmids carry one virulence factor, a gene encoding a cellulase, CelA in case of pCM1 and a putative serine protease Pat-1 on pCM2. These genes can independently convert the non-virulent strain CMM100 into a pathogen causing wilt on tomatoes. Currently, genome projects for Cmm and the closely related potato-pathogen C. michiganensis subsp. sepedonicus have been initiated. The data from the genome project shall give clues on further genes involved in plant-microbe interaction that can be tested experimentally. Especially, identification of genes related to host-specificity through genome comparison of the two subspecies might be possible.

Healthy plants: necessary for a balanced 'One Health' concept.

PubMed

Fletcher, Jacqueline; Franz, David; Leclerc, J Eugene

2009-01-01

All life forms depend ultimately upon sunlight to create the energy 'currency' required for the functions of living. Green plants can make that conversion directly but the rest of us would perish without access to foods derived, directly or indirectly, from plants. We also require their fibre which we use for clothing, building and other purposes. However, plants, just as humans and animals, are attacked by pathogens that cause a myriad of symptoms that can lead to reduced yields, lower quality products and diminished nutritional value. Plant pathogens share many features with their human and animal counterparts. Some pathogens - whether of humans, animals, or plants - have nimble genomes or the ability to pirate genes from other organisms via mobile elements. Some have developed the ability to cross kingdoms in their host ranges. Many others share virulence factors, such as the type III secretion system (T3SS) or mechanisms for sensing population density, that work equally well in all kingdoms. Certain pathogens of hosts in all kingdoms rely upon insect vectors and use similar mechanisms to ensure dispersal (and sometimes survival) in this way. Plant-pathogen interactions have more direct consequence for humans when the microbes are human pathogens such as Escherichia coli 0157:H7 and Salmonella spp., which can contaminate fresh produce or when they produce metabolites, such as mycotoxins, which are harmful when consumed. Finally, national biosecurity concerns and the need for prevention, preparedness and forensic capabilities cross all kingdom barriers. Thus, our communities that focus on one of these kingdoms have much to learn from one another and a complete and balanced 'One Health' initiative must be tripartite, embracing the essential components of healthy plants, healthy animals and healthy people.

The potential of pathogens as biological control of parthenium weed (Parthenium hysterophorus L.) in Ethiopia.

PubMed

Taye, T; Gossmann, M; Einhorn, G; Büttner, C; Metz, R; Abate, D

2002-01-01

P. hsyterophorus is an exotic invasive annual weed now causing severe infestation in Ethiopia. Studies on diagnosis, incidence and distribution of pathogens associated with parthenium weed in Ethiopia were carried out from 1998-2002. Several fungal isolates were obtained from seed and other parts of parthenium plants. Among them were putative pathogenic fungal species of the genus Helminthosporium, Phoma, Curvularia, Chaetomium, Alternaria, and Fusarium. However, pathogenecity test of the isolates obtained showed no or non-specific symptoms. It was concluded that these pathogens could be opportunistic with insignificant potential for biological control of parthenium. Two most important diseases associated with parthenium were a rust disease, caused by Puccinia abrupta var. partheniicola, and a phyllody disease, caused by a phytoplasma of fababean phyllody (PBP) phytoplasma group. The rust was commonly found in cool mid altitude (1500-2500 m) areas while phyllody was observed in low to mid altitude regions (900-2500 m) of Ethiopia, with a disease incidence up to 100% and 75%, respectively, in some locations. Study of the individual effects of the rust and phyllody diseases under field conditions showed a reduction on weed morphological parameters (plant height, leaf area, and dry matter yield). Parthenium seed production was reduced by 42% and 85% due to rust and phyllody, respectively. Phyllody and rust diseases of parthenium showed significant potential for classical biological control of parthenium after further confirmation of insect vectors that transmit phyllody and host range of phyllody disease to the related economic plants in Ethiopia.

N-Acetylcysteine in Agriculture, a Novel Use for an Old Molecule: Focus on Controlling the Plant–Pathogen Xylella fastidiosa

PubMed Central

Muranaka, Lígia S.; Giorgiano, Thais E.; Takita, Marco A.; Forim, Moacir R.; Silva, Luis F. C.; Coletta-Filho, Helvécio D.; Machado, Marcos A.; de Souza, Alessandra A.

2013-01-01

Xylella fastidiosa is a plant pathogen bacterium that causes diseases in many different crops. In citrus, it causes Citrus Variegated Chlorosis (CVC). The mechanism of pathogenicity of this bacterium is associated with its capacity to colonize and form a biofilm in the xylem vessels of host plants, and there is not yet any method to directly reduce populations of this pathogen in the field. In this study, we investigated the inhibitory effect of N-Acetylcysteine (NAC), a cysteine analogue used mainly to treat human diseases, on X. fastidiosa in different experimental conditions. Concentrations of NAC over 1 mg/mL reduced bacterial adhesion to glass surfaces, biofilm formation and the amount of exopolysaccharides (EPS). The minimal inhibitory concentration of NAC was 6 mg/mL. NAC was supplied to X. fastidiosa-infected plants in hydroponics, fertigation, and adsorbed to organic fertilizer (NAC-Fertilizer). HPLC analysis indicated that plants absorbed NAC at concentrations of 0.48 and 2.4 mg/mL but not at 6 mg/mL. Sweet orange plants with CVC symptoms treated with NAC (0.48 and 2.4 mg/mL) in hydroponics showed clear symptom remission and reduction in bacterial population, as analyzed by quantitative PCR and bacterial isolation. Experiments using fertigation and NAC-Fertilizer were done to simulate a condition closer to that normally is used in the field. For both, significant symptom remission and a reduced bacterial growth rate were observed. Using NAC-Fertilizer the lag for resurgence of symptoms on leaves after interruption of the treatment increased to around eight months. This is the first report of the anti-bacterial effect of NAC against a phytopathogenic bacterium. The results obtained in this work together with the characteristics of this molecule indicate that the use of NAC in agriculture might be a new and sustainable strategy for controlling plant pathogenic bacteria. PMID:24009716

Characterisation of a flavonoid ligand of the fungal protein Alt a 1

PubMed Central

Garrido-Arandia, María; Silva-Navas, Javier; Ramírez-Castillejo, Carmen; Cubells-Baeza, Nuria; Gómez-Casado, Cristina; Barber, Domingo; Pozo, Juan C.; Melendi, Pablo G.; Pacios, Luis F.; Díaz-Perales, Araceli

2016-01-01

Spores of pathogenic fungi are virtually ubiquitous and cause human disease and severe losses in crops. The endophytic fungi Alternaria species produce host-selective phytotoxins. Alt a 1 is a strongly allergenic protein found in A. alternata that causes severe asthma. Despite the well-established pathogenicity of Alt a 1, the molecular mechanisms underlying its action and physiological function remain largely unknown. To gain insight into the role played by this protein in the pathogenicity of the fungus, we studied production of Alt a 1 and its activity in spores. We found that Alt a 1 accumulates inside spores and that its release with a ligand is pH-dependent, with optimum production in the 5.0–6.5 interval. The Alt a 1 ligand was identified as a methylated flavonoid that inhibits plant root growth and detoxifies reactive oxygen species. We also found that Alt a 1 changes its oligomerization state depending on the pH of the surrounding medium and that these changes facilitate the release of the ligand. Based on these results, we propose that release of Alt a 1 should be a pathogenic target in approaches used to block plant defenses and consequently to favor fungal entry into the plant. PMID:27633190

Characterisation of a flavonoid ligand of the fungal protein Alt a 1.

PubMed

Garrido-Arandia, María; Silva-Navas, Javier; Ramírez-Castillejo, Carmen; Cubells-Baeza, Nuria; Gómez-Casado, Cristina; Barber, Domingo; Pozo, Juan C; Melendi, Pablo G; Pacios, Luis F; Díaz-Perales, Araceli

2016-09-16

Spores of pathogenic fungi are virtually ubiquitous and cause human disease and severe losses in crops. The endophytic fungi Alternaria species produce host-selective phytotoxins. Alt a 1 is a strongly allergenic protein found in A. alternata that causes severe asthma. Despite the well-established pathogenicity of Alt a 1, the molecular mechanisms underlying its action and physiological function remain largely unknown. To gain insight into the role played by this protein in the pathogenicity of the fungus, we studied production of Alt a 1 and its activity in spores. We found that Alt a 1 accumulates inside spores and that its release with a ligand is pH-dependent, with optimum production in the 5.0-6.5 interval. The Alt a 1 ligand was identified as a methylated flavonoid that inhibits plant root growth and detoxifies reactive oxygen species. We also found that Alt a 1 changes its oligomerization state depending on the pH of the surrounding medium and that these changes facilitate the release of the ligand. Based on these results, we propose that release of Alt a 1 should be a pathogenic target in approaches used to block plant defenses and consequently to favor fungal entry into the plant.

Soil mixture composition alters Arabidopsis susceptibility to Pseudomonas syringae infection

USDA-ARS?s Scientific Manuscript database

Pseudomonas syringae is a Gram-negative bacterial pathogen that causes disease on more than 100 different plant species, including the model plant Arabidopsis thaliana. Dissection of the Arabidopsis thaliana-Pseudomonas syringae pathosystem has identified many factors that contribute to successful ...

First report of an Armillaria root disease pathogen, Armillaria gallica, associated with several new hosts in Hawaii

Treesearch

M.-S. Kim; J. W. Hanna; N. B. Klopfenstein

2010-01-01

The loss and decline of native tree species caused by invasive plant pathogens is a major threat to the endangered endemic forests of the Hawaiian Islands (3). Thus, it is critical to characterize existing pathogens to evaluate potential invasiveness. In August 2005, rhizomorphs and mycelial bark fans of genet HI-4 were collected from dead/declining, mature trees of...

Biofilm formation by pathogenic Prototheca algae.

PubMed

Kwiecinski, J

2015-12-01

Prototheca microalgae are the only plants known to cause infections in humans and animals. The mechanisms of Prototheca infections are poorly understood, and no good treatments are available. Biofilms-surface-attached, three-dimensional microbial communities contributing to chronic infections-are formed by many pathogenic bacteria and fungi, but it is not known if Prototheca algae also have this ability. This study shows that various Prototheca species form biofilms composed of surface-attached cells in all growth phases, linked together by matrix containing DNA and polysaccharides. Biofilm formation was modulated by the presence of host plasma or milk. Compared to planktonic cells, Prototheca biofilms caused decreased release of IL-6 by mononuclear immune cells and responded differently to treatment with antimicrobials. Prototheca biofilms possibly contribute to chronic and hard-to-treat character of those algal infections. Prototheca algae are the only existing pathogenic plants. Almost nothing is known about mechanisms of Prototheca infections. This study identifies that, similar to pathogenic bacteria and fungi, Prototheca algae can form biofilms. These biofilms induce reduced immune cell activation relative to planktonic cells, and are also less susceptible to antimicrobials. Biofilm formation by Prototheca could be the first in vitro correlate of pathogenicity, opening a new research field for this pathogen. © 2015 The Society for Applied Microbiology.

Mycosphaerella fijiensis, the black leaf streak pathogen of banana: progress towards understanding pathogen biology and detection, disease development, and the challenges of control.

PubMed

Churchill, Alice C L

2011-05-01

Banana (Musa spp.) is grown throughout the tropical and subtropical regions of the world. The fruits are a key staple food in many developing countries and a source of income for subsistence farmers. Bananas are also a major, multibillion-dollar export commodity for consumption primarily in developed countries, where few banana cultivars are grown. The fungal pathogen Mycosphaerella fijiensis causes black leaf streak disease (BLSD; aka black Sigatoka leaf spot) on the majority of edible banana cultivars grown worldwide. The fact that most of these cultivars are sterile and unsuitable for the breeding of resistant lines necessitates the extensive use of fungicides as the primary means of disease control. BLSD is a significant threat to the food security of resource-poor populations who cannot afford fungicides, and increases the environmental and health hazards where large-acreage monocultures of banana (Cavendish subgroup, AAA genome) are grown for export. Mycosphaerella fijiensis M. Morelet is a sexual, heterothallic fungus having Pseudocercospora fijiensis (M. Morelet) Deighton as the anamorph stage. It is a haploid, hemibiotrophic ascomycete within the class Dothideomycetes, order Capnodiales and family Mycosphaerellaceae. Its taxonomic placement is based on DNA phylogeny, morphological analyses and cultural characteristics. Mycosphaerella fijiensis is a leaf pathogen that causes reddish-brown streaks running parallel to the leaf veins, which aggregate to form larger, dark-brown to black compound streaks. These streaks eventually form fusiform or elliptical lesions that coalesce, form a water-soaked border with a yellow halo and, eventually, merge to cause extensive leaf necrosis. The disease does not kill the plants immediately, but weakens them by decreasing the photosynthetic capacity of leaves, causing a reduction in the quantity and quality of fruit, and inducing the premature ripening of fruit harvested from infected plants. Although Musa spp. are the primary hosts of M. fijiensis, the ornamental plant Heliconia psittacorum has been reported as an alternative host. Several valuable tools and resources have been developed to overcome some of the challenges of studying this host-pathogen system. These include a DNA-mediated fungal transformation system and the ability to conduct targeted gene disruptions, reliable quantitative plant bioassays, diagnostic probes to detect and differentiate M. fijiensis from related pathogens and to distinguish strains of different mating types, and a genome sequence that has revealed a wealth of gene sequences and molecular markers to be utilized in functional and population biology studies. http://bananas.bioversityinternational.org/, http://genome.jgi-psf.org/Mycfi2/Mycfi2.home.html, http://www.isppweb.org/names_banana_pathogen.asp#fun, http://www.promusa.org/. © 2010 THE AUTHOR. MOLECULAR PLANT PATHOLOGY © 2010 BSPP AND BLACKWELL PUBLISHING LTD.

A De Novo-Assembly Based Data Analysis Pipeline for Plant Obligate Parasite Metatranscriptomic Studies.

PubMed

Guo, Li; Allen, Kelly S; Deiulio, Greg; Zhang, Yong; Madeiras, Angela M; Wick, Robert L; Ma, Li-Jun

2016-01-01

Current and emerging plant diseases caused by obligate parasitic microbes such as rusts, downy mildews, and powdery mildews threaten worldwide crop production and food safety. These obligate parasites are typically unculturable in the laboratory, posing technical challenges to characterize them at the genetic and genomic level. Here we have developed a data analysis pipeline integrating several bioinformatic software programs. This pipeline facilitates rapid gene discovery and expression analysis of a plant host and its obligate parasite simultaneously by next generation sequencing of mixed host and pathogen RNA (i.e., metatranscriptomics). We applied this pipeline to metatranscriptomic sequencing data of sweet basil (Ocimum basilicum) and its obligate downy mildew parasite Peronospora belbahrii, both lacking a sequenced genome. Even with a single data point, we were able to identify both candidate host defense genes and pathogen virulence genes that are highly expressed during infection. This demonstrates the power of this pipeline for identifying genes important in host-pathogen interactions without prior genomic information for either the plant host or the obligate biotrophic pathogen. The simplicity of this pipeline makes it accessible to researchers with limited computational skills and applicable to metatranscriptomic data analysis in a wide range of plant-obligate-parasite systems.

Biocontrol mechanism by root-associated Bacillus amyloliquefaciens FZB42 – a review

PubMed Central

Chowdhury, Soumitra Paul; Hartmann, Anton; Gao, XueWen; Borriss, Rainer

2015-01-01

Bacillus amyloliquefaciens subsp. plantarum FZB42 is a Gram-positive model bacterium for unraveling plant–microbe interactions in Bacilli. In addition, FZB42 is used commercially as biofertilizer and biocontrol agent in agriculture. Genome analysis of FZB42 revealed that nearly 10% of the FZB42 genome is devoted to synthesizing antimicrobial metabolites and their corresponding immunity genes. However, recent investigations in planta demonstrated that – except surfactin – the amount of such compounds found in vicinity of plant roots is relatively low, making doubtful a direct function in suppressing competing microflora including plant pathogens. These metabolites have been also suspected to induce changes within the rhizosphere microbial community, which might affect environment and plant health. However, sequence analysis of rhizosphere samples revealed only marginal changes in the root microbiome, suggesting that secondary metabolites are not the key factor in protecting plants from pathogenic microorganisms. On the other hand, adding FZB42 to plants compensate, at least in part, changes in the community structure caused by the pathogen, indicating an interesting mechanism of plant protection by beneficial Bacilli. Sub-lethal concentrations of cyclic lipopeptides and volatiles produced by plant-associated Bacilli trigger pathways of induced systemic resistance (ISR), which protect plants against attacks of pathogenic microbes, viruses, and nematodes. Stimulation of ISR by bacterial metabolites is likely the main mechanism responsible for biocontrol action of FZB42. PMID:26284057

A new approach for detecting fungal and oomycete plant pathogens in next generation sequencing metagenome data utilising electronic probes

USDA-ARS?s Scientific Manuscript database

Early stage infections caused by fungal/oomycete spores can remain undetected until signs or symptoms develop. Serological and molecular techniques are currently used for detecting these pathogens. Next-generation sequencing (NGS) has potential as a diagnostic tool, due to the capacity to target mul...

Using hierarchical clustering of secreted protein families to classify and rank candidate effectors of rust fungi

USDA-ARS?s Scientific Manuscript database

Rust fungi are obligate biotrophic pathogens causing considerable damage on crop plants. P. graminis f. sp. tritici, the causal agent of wheat stem rust, and M. larici-populina, the poplar rust pathogen, have strong deleterious impact on wheat and poplar wood production, respectively. The recently r...

The role of Xylella fastidiosa cold shock proteins in Pierce’s disease of grapes

USDA-ARS?s Scientific Manuscript database

Pierce’s disease of grapevine, caused by the bacterial pathogen Xylella fastidiosa (Xf) is limited to warmer climates, and plant infection can be eliminated by cold winter conditions. Milder winters can increase the likelihood of pathogen persistence from one growing season to the next. Cold adaptat...

Similarities and differences in global gene expression profiles between herbicide- and pathogen-induced PSII inhibition

USDA-ARS?s Scientific Manuscript database

Plant pathogens, and photosynthesis inhibiting herbicides, can both damage photosystem II (PSII), causing it to be highly sensitive to damage by light energy, and to release high levels of reactive oxygen species (ROS). This photoinhibition of PSII could possibly be the source of the strong oxidativ...

Quantitative trait loci for resistance to two fungal pathogens in Quercus robur

Treesearch

Cécile Robin; Amira Mougou-Hamdane; Jean-Marc Gion; Antoine Kremer; Marie-Laure Desprez-Loustau

2012-01-01

Powdery mildew, caused by Erysiphe alphitoides (Ascomycete), is the most frequent disease of oaks, which are also known to be host plants for Phytophthora cinnamomi (Oomycete), the causal agent of ink disease. Components of genetic resistance to these two pathogens, infecting either leaves or root and collar, were...

Estimating the Effectiveness of Imidacloprid When Used to Suppress Transmission of Tomato spotted wilt orthotospovirus in Commercial Agriculture.

PubMed

Chappell, Thomas M; Kennedy, George G

2018-06-21

Imidacloprid is widely used to manage tomato spotted wilt disease (TSW) in tobacco, tomato, and pepper, caused by Tomato spotted wilt orthotospovirus (TSWV) and spread by the tobacco thrips, Frankliniella fusca Hinds (Thysanoptera: Thripidae). Imidacloprid suppresses transmission of TSWV by reducing probing and feeding by adult thrips on treated plants, thereby reducing the probability of transmission by infectious thrips. Because imidacloprid does not reduce probing and feeding on treated plants to zero, the reduction in transmission probability per viruliferous thrips can be offset by an increase in the number of viruliferous thrips challenging treated plants. A composite of these effects which we call 'pathogen pressure' experienced by plants is a function of thrips population size, the proportion of those thrips that are viruliferous, and the probability that viruliferous thrips successfully inoculate plants. To better understand the relationship between imidacloprid's effect on virus transmission, pathogen pressure, and TSW incidence in tobacco, we modeled TSW incidence as a function of the two most important variables affecting components of pathogen pressure, temperature, and precipitation, and the dependence of imidacloprid's effect on pathogen pressure. A model incorporating imidacloprid's effect as a reduction in pathogen pressure was found to be more descriptive than models incorporating the effect as a reduction in TSW incidence. Results reveal maximum proportional reduction in TSW incidence resulting from imidacloprid use is associated with minimal potential TSW incidence. As pathogen pressure increases, potential TSW incidence approaches 100%, and the benefits of imidacloprid use are highest at intermediate levels of pathogen pressure.

Plant-Associated Symbiotic Burkholderia Species Lack Hallmark Strategies Required in Mammalian Pathogenesis

PubMed Central

Fong, Stephanie; Yerrapragada, Shailaja; Estrada-de los Santos, Paulina; Yang, Paul; Song, Nannie; Kano, Stephanie; de Faria, Sergio M.; Dakora, Felix D.; Weinstock, George; Hirsch, Ann M.

2014-01-01

Burkholderia is a diverse and dynamic genus, containing pathogenic species as well as species that form complex interactions with plants. Pathogenic strains, such as B. pseudomallei and B. mallei, can cause serious disease in mammals, while other Burkholderia strains are opportunistic pathogens, infecting humans or animals with a compromised immune system. Although some of the opportunistic Burkholderia pathogens are known to promote plant growth and even fix nitrogen, the risk of infection to infants, the elderly, and people who are immunocompromised has not only resulted in a restriction on their use, but has also limited the application of non-pathogenic, symbiotic species, several of which nodulate legume roots or have positive effects on plant growth. However, recent phylogenetic analyses have demonstrated that Burkholderia species separate into distinct lineages, suggesting the possibility for safe use of certain symbiotic species in agricultural contexts. A number of environmental strains that promote plant growth or degrade xenobiotics are also included in the symbiotic lineage. Many of these species have the potential to enhance agriculture in areas where fertilizers are not readily available and may serve in the future as inocula for crops growing in soils impacted by climate change. Here we address the pathogenic potential of several of the symbiotic Burkholderia strains using bioinformatics and functional tests. A series of infection experiments using Caenorhabditis elegans and HeLa cells, as well as genomic characterization of pathogenic loci, show that the risk of opportunistic infection by symbiotic strains such as B. tuberum is extremely low. PMID:24416172

Sentinel Trees as a Tool to Forecast Invasions of Alien Plant Pathogens

PubMed Central

Vettraino, AnnaMaria; Roques, Alain; Yart, Annie; Fan, Jian-ting; Sun, Jiang-hua; Vannini, Andrea

2015-01-01

Recent disease outbreaks caused by alien invasive pathogens into European forests posed a serious threat to forest sustainability with relevant environmental and economic effects. Many of the alien tree pathogens recently introduced into Europe were not previously included on any quarantine lists, thus they were not subject to phytosanitary inspections. The identification and description of alien fungi potentially pathogenic to native European flora before their introduction in Europe, is a paramount need in order to limit the risk of invasion and the impact to forest ecosystems. To determine the potential invasive fungi, a sentinel trees plot was established in Fuyang, China, using healthy seedlings of European tree species including Quercus petreae, Q. suber, and Q. ilex. The fungal assemblage associated with symptomatic specimens was studied using the tag-encoded 454 pyrosequencing of the nuclear ribosomal internal transcribed spacer-1 (ITS 1). Taxa with probable Asiatic origin were identified and included plant pathogenic genera. These results indicate that sentinel plants may be a strategic tool to improve the prevention of bioinvasions. PMID:25826684

Chitosan-induced immunity in Camellia sinensis (L.) O. Kuntze against blister blight disease is mediated by nitric-oxide.

PubMed

Chandra, Swarnendu; Chakraborty, Nilanjan; Panda, Koustubh; Acharya, Krishnendu

2017-06-01

Blister blight disease, caused by an obligate biotrophic fungal pathogen, Exobasidium vexans Massee is posing a serious threat for tea cultivation in Asia. As the use of chemical pesticides on tea leaves substantially increases the toxic risks of tea consumption, serious attempts are being made to control such pathogens by boosting the intrinsic natural defense responses against invading pathogens in tea plants. In this study, the nature and durability of resistance offered by chitosan and the possible mechanism of chitosan-induced defense induction in Camellia sinensis (L.) O. Kuntze plants against blister blight disease were investigated. Foliar application of 0.01% chitosan solution at 15 days interval not only reduced the blister blight incidence for two seasons, but also maintained the induced expressions of different defense related enzymes and total phenol content compared to the control. Defense responses induced by chitosan were found to be down regulated under nitric oxide (NO) deficient conditions in vivo, indicating that the observed chitosan-induced resistance is probably activated via NO signaling. Such role of NO in host defense response was further established by application of the NO donor, sodium nitroprusside (SNP), which produced similar defense responses accomplished through chitosan treatment. Taken together, our results suggest that increased production of NO in chitosan-treated tea plants may play a critical role in triggering the innate defense responses effective against plant pathogens, including that causing the blister blight disease. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Analyses of Xylella whole genome sequences and proposal of Xylella taiwanensis sp. nov.

USDA-ARS?s Scientific Manuscript database

Xylella fastidiosa is a Gram negative, xylem limited and nutritionally fastidious plant pathogenic bacterium that cause disease in many economically important plants. A single species, fastidiosa, with three subspecies (fastidiosa, multiplex, and pauca) have been described. Most Xylella strains were...

Bacterial subfamily of LuxR regulators that respond to plant compounds

USDA-ARS?s Scientific Manuscript database

Certain strains of Pseudomonas fluorescens inhabit the rhizosphere where they can suppress plant diseases caused by soilborne pathogens. The expression of genes coding for the biosynthesis of antibiotics is crucial to the biological control properties of these bacteria, but factors influencing the ...

Insect pathogenicity in plant-beneficial pseudomonads: phylogenetic distribution and comparative genomics.

PubMed

Flury, Pascale; Aellen, Nora; Ruffner, Beat; Péchy-Tarr, Maria; Fataar, Shakira; Metla, Zane; Dominguez-Ferreras, Ana; Bloemberg, Guido; Frey, Joachim; Goesmann, Alexander; Raaijmakers, Jos M; Duffy, Brion; Höfte, Monica; Blom, Jochen; Smits, Theo H M; Keel, Christoph; Maurhofer, Monika

2016-10-01

Bacteria of the genus Pseudomonas occupy diverse environments. The Pseudomonas fluorescens group is particularly well-known for its plant-beneficial properties including pathogen suppression. Recent observations that some strains of this group also cause lethal infections in insect larvae, however, point to a more versatile ecology of these bacteria. We show that 26 P. fluorescens group strains, isolated from three continents and covering three phylogenetically distinct sub-clades, exhibited different activities toward lepidopteran larvae, ranging from lethal to avirulent. All strains of sub-clade 1, which includes Pseudomonas chlororaphis and Pseudomonas protegens, were highly insecticidal regardless of their origin (animals, plants). Comparative genomics revealed that strains in this sub-clade possess specific traits allowing a switch between plant- and insect-associated lifestyles. We identified 90 genes unique to all highly insecticidal strains (sub-clade 1) and 117 genes common to all strains of sub-clade 1 and present in some moderately insecticidal strains of sub-clade 3. Mutational analysis of selected genes revealed the importance of chitinase C and phospholipase C in insect pathogenicity. The study provides insight into the genetic basis and phylogenetic distribution of traits defining insecticidal activity in plant-beneficial pseudomonads. Strains with potent dual activity against plant pathogens and herbivorous insects have great potential for use in integrated pest management for crops.

Insect pathogenicity in plant-beneficial pseudomonads: phylogenetic distribution and comparative genomics

PubMed Central

Flury, Pascale; Aellen, Nora; Ruffner, Beat; Péchy-Tarr, Maria; Fataar, Shakira; Metla, Zane; Dominguez-Ferreras, Ana; Bloemberg, Guido; Frey, Joachim; Goesmann, Alexander; Raaijmakers, Jos M; Duffy, Brion; Höfte, Monica; Blom, Jochen; Smits, Theo H M; Keel, Christoph; Maurhofer, Monika

2016-01-01

Bacteria of the genus Pseudomonas occupy diverse environments. The Pseudomonas fluorescens group is particularly well-known for its plant-beneficial properties including pathogen suppression. Recent observations that some strains of this group also cause lethal infections in insect larvae, however, point to a more versatile ecology of these bacteria. We show that 26 P. fluorescens group strains, isolated from three continents and covering three phylogenetically distinct sub-clades, exhibited different activities toward lepidopteran larvae, ranging from lethal to avirulent. All strains of sub-clade 1, which includes Pseudomonas chlororaphis and Pseudomonas protegens, were highly insecticidal regardless of their origin (animals, plants). Comparative genomics revealed that strains in this sub-clade possess specific traits allowing a switch between plant- and insect-associated lifestyles. We identified 90 genes unique to all highly insecticidal strains (sub-clade 1) and 117 genes common to all strains of sub-clade 1 and present in some moderately insecticidal strains of sub-clade 3. Mutational analysis of selected genes revealed the importance of chitinase C and phospholipase C in insect pathogenicity. The study provides insight into the genetic basis and phylogenetic distribution of traits defining insecticidal activity in plant-beneficial pseudomonads. Strains with potent dual activity against plant pathogens and herbivorous insects have great potential for use in integrated pest management for crops. PMID:26894448

Comparative genomics of the Fusarium fujikuroi species complex: biosynthetic pathways metabolite production and plant pathogenicity

USDA-ARS?s Scientific Manuscript database

Fusarium is a huge genus of filamentous fungi causing plant diseases in a wide range of host plants that result in high economic losses to world agriculture every year. Phylogenetic studies have shown that the genus Fusarium consists of different species complexes. One of them is the “Fusarium fujik...

Advanced DNA-Based Point-of-Care Diagnostic Methods for Plant Diseases Detection.

PubMed

Lau, Han Yih; Botella, Jose R

2017-01-01

Diagnostic technologies for the detection of plant pathogens with point-of-care capability and high multiplexing ability are an essential tool in the fight to reduce the large agricultural production losses caused by plant diseases. The main desirable characteristics for such diagnostic assays are high specificity, sensitivity, reproducibility, quickness, cost efficiency and high-throughput multiplex detection capability. This article describes and discusses various DNA-based point-of care diagnostic methods for applications in plant disease detection. Polymerase chain reaction (PCR) is the most common DNA amplification technology used for detecting various plant and animal pathogens. However, subsequent to PCR based assays, several types of nucleic acid amplification technologies have been developed to achieve higher sensitivity, rapid detection as well as suitable for field applications such as loop-mediated isothermal amplification, helicase-dependent amplification, rolling circle amplification, recombinase polymerase amplification, and molecular inversion probe. The principle behind these technologies has been thoroughly discussed in several review papers; herein we emphasize the application of these technologies to detect plant pathogens by outlining the advantages and disadvantages of each technology in detail.

Advanced DNA-Based Point-of-Care Diagnostic Methods for Plant Diseases Detection

PubMed Central

Lau, Han Yih; Botella, Jose R.

2017-01-01

Diagnostic technologies for the detection of plant pathogens with point-of-care capability and high multiplexing ability are an essential tool in the fight to reduce the large agricultural production losses caused by plant diseases. The main desirable characteristics for such diagnostic assays are high specificity, sensitivity, reproducibility, quickness, cost efficiency and high-throughput multiplex detection capability. This article describes and discusses various DNA-based point-of care diagnostic methods for applications in plant disease detection. Polymerase chain reaction (PCR) is the most common DNA amplification technology used for detecting various plant and animal pathogens. However, subsequent to PCR based assays, several types of nucleic acid amplification technologies have been developed to achieve higher sensitivity, rapid detection as well as suitable for field applications such as loop-mediated isothermal amplification, helicase-dependent amplification, rolling circle amplification, recombinase polymerase amplification, and molecular inversion probe. The principle behind these technologies has been thoroughly discussed in several review papers; herein we emphasize the application of these technologies to detect plant pathogens by outlining the advantages and disadvantages of each technology in detail. PMID:29375588

Transcriptome and Metabolite Profiling of the Infection Cycle of Zymoseptoria tritici on Wheat Reveals a Biphasic Interaction with Plant Immunity Involving Differential Pathogen Chromosomal Contributions and a Variation on the Hemibiotrophic Lifestyle Definition1[OPEN

PubMed Central

Rudd, Jason J.; Kanyuka, Kostya; Hassani-Pak, Keywan; Derbyshire, Mark; Andongabo, Ambrose; Devonshire, Jean; Lysenko, Artem; Saqi, Mansoor; Desai, Nalini M.; Powers, Stephen J.; Hooper, Juliet; Ambroso, Linda; Bharti, Arvind; Farmer, Andrew; Hammond-Kosack, Kim E.; Dietrich, Robert A.; Courbot, Mikael

2015-01-01

The hemibiotrophic fungus Zymoseptoria tritici causes Septoria tritici blotch disease of wheat (Triticum aestivum). Pathogen reproduction on wheat occurs without cell penetration, suggesting that dynamic and intimate intercellular communication occurs between fungus and plant throughout the disease cycle. We used deep RNA sequencing and metabolomics to investigate the physiology of plant and pathogen throughout an asexual reproductive cycle of Z. tritici on wheat leaves. Over 3,000 pathogen genes, more than 7,000 wheat genes, and more than 300 metabolites were differentially regulated. Intriguingly, individual fungal chromosomes contributed unequally to the overall gene expression changes. Early transcriptional down-regulation of putative host defense genes was detected in inoculated leaves. There was little evidence for fungal nutrient acquisition from the plant throughout symptomless colonization by Z. tritici, which may instead be utilizing lipid and fatty acid stores for growth. However, the fungus then subsequently manipulated specific plant carbohydrates, including fructan metabolites, during the switch to necrotrophic growth and reproduction. This switch coincided with increased expression of jasmonic acid biosynthesis genes and large-scale activation of other plant defense responses. Fungal genes encoding putative secondary metabolite clusters and secreted effector proteins were identified with distinct infection phase-specific expression patterns, although functional analysis suggested that many have overlapping/redundant functions in virulence. The pathogenic lifestyle of Z. tritici on wheat revealed through this study, involving initial defense suppression by a slow-growing extracellular and nutritionally limited pathogen followed by defense (hyper) activation during reproduction, reveals a subtle modification of the conceptual definition of hemibiotrophic plant infection. PMID:25596183

Drought Impact on the Soilborne Fungal Pathogen of Tomato: Fusarium Oxysporum f. sp. Lycopersici Race 3

NASA Astrophysics Data System (ADS)

Raju, T.

2016-12-01

This paper reviews the drought impact on fungal pathogen of tomato. It presents the 11 Main Procedures used to conduct the experiments and discusses materials used. The 11 procedures are: Gather All the Soils, Sterilize the Soils Using Auto-Clave, Water Retention Test Using Auto-Clave, Cultivate Pathogen, Grow Tomato Plant, Count Pathogenic Cells, Inoculate the Pathogen, Conduct Root Dip, Grow Positive and Negative Samples, Test for Fusarium, and the Soil Separation Experiment with Pathogenic Soil. Experiments conducted on 6 Main Soils used in farming throughout California. The Yolo Series, Whiterock Series, Euic Soil, Potting Soil, Blacklock Series, and Henneke Series. The 6 Soils include amounts of clay, silt, sand, loam, and humus. It was crucial that these soils include these properties because deriving from last year's research I found that these particles in the soil has a role in the growth of the plant. Next, I tested the dry/wet weight of the soils, as this gave me a good estimate of how much water the soils can retain. This is very important because I found a direct correlation between the soil that retained the most amount of water and the soil that had the least harms done. Next, the other labs were completed to cultivate, inoculate, and test the pathogens in the soil, now these steps must be carried out with accuracy and precision because pathogens are a biological agent that causes disease or illness to its host, and if even 0.100 mL is changed in the pathogenic level it can make a large difference. Later, after I finished conducting the root dip, and raising the tomato plants. I counted the Fusarium count in the soil and plated the samples, where I was able to find the results on how much harm the pathogen had on the plant. In each of the 90 reps. the Fusarium (soilborne pathogen) decreased a little, which factors in the transfer from Potato Dextrose Agar Petri Dish to the Soils. After, this transfer the pathogen decreased and never increased, but from my Pathogen Severity Experiment, the harms done to the Early Pak 7 Tomato Plants were much greater, in soils with lower amounts of pathogen. This is because the pathogen was dying in soils with low water content, and dry material. Since, the soil was poor the plant's vascular system was weak, thus it was easier for a small Colony Forming Unit to weaken the plant and eventually kill it.

Glacial Refugia in Pathogens: European Genetic Structure of Anther Smut Pathogens on Silene latifolia and Silene dioica

PubMed Central

Vercken, Elodie; Fontaine, Michael C.; Gladieux, Pierre; Hood, Michael E.; Jonot, Odile; Giraud, Tatiana

2010-01-01

Climate warming is predicted to increase the frequency of invasions by pathogens and to cause the large-scale redistribution of native host species, with dramatic consequences on the health of domesticated and wild populations of plants and animals. The study of historic range shifts in response to climate change, such as during interglacial cycles, can help in the prediction of the routes and dynamics of infectious diseases during the impending ecosystem changes. Here we studied the population structure in Europe of two Microbotryum species causing anther smut disease on the plants Silene latifolia and Silene dioica. Clustering analyses revealed the existence of genetically distinct groups for the pathogen on S. latifolia, providing a clear-cut example of European phylogeography reflecting recolonization from southern refugia after glaciation. The pathogen genetic structure was congruent with the genetic structure of its host species S. latifolia, suggesting dependence of the migration pathway of the anther smut fungus on its host. The fungus, however, appeared to have persisted in more numerous and smaller refugia than its host and to have experienced fewer events of large-scale dispersal. The anther smut pathogen on S. dioica also showed a strong phylogeographic structure that might be related to more northern glacial refugia. Differences in host ecology probably played a role in these differences in the pathogen population structure. Very high selfing rates were inferred in both fungal species, explaining the low levels of admixture between the genetic clusters. The systems studied here indicate that migration patterns caused by climate change can be expected to include pathogen invasions that follow the redistribution of their host species at continental scales, but also that the recolonization by pathogens is not simply a mirror of their hosts, even for obligate biotrophs, and that the ecology of hosts and pathogen mating systems likely affects recolonization patterns. PMID:21187901

The role of effectors and host immunity in plant–necrotrophic fungal interactions

PubMed Central

Wang, Xuli; Jiang, Nan; Liu, Jinling; Liu, Wende; Wang, Guo-Liang

2014-01-01

Fungal diseases pose constant threats to the global economy and food safety. As the largest group of plant fungal pathogens, necrotrophic fungi cause heavy crop losses worldwide. The molecular mechanisms of the interaction between necrotrophic fungi and plants are complex and involve sophisticated recognition and signaling networks. Here, we review recent findings on the roles of phytotoxin and proteinaceous effectors, pathogen-associated molecular patterns (PAMPs), and small RNAs from necrotrophic fungi. We also consider the functions of damage-associated molecular patterns (DAMPs), the receptor-like protein kinase BIK1, and epigenetic regulation in plant immunity to necrotrophic fungi. PMID:25513773

Emerging oomycete threats to plants and animals

PubMed Central

Chaparro-Garcia, Angela

2016-01-01

Oomycetes, or water moulds, are fungal-like organisms phylogenetically related to algae. They cause devastating diseases in both plants and animals. Here, we describe seven oomycete species that are emerging or re-emerging threats to agriculture, horticulture, aquaculture and natural ecosystems. They include the plant pathogens Phytophthora infestans, Phytophthora palmivora, Phytophthora ramorum, Plasmopara obducens, and the animal pathogens Aphanomyces invadans, Saprolegnia parasitica and Halioticida noduliformans. For each species, we describe its pathology, importance and impact, discuss why it is an emerging threat and briefly review current research activities. This article is part of the themed issue ‘Tackling emerging fungal threats to animal health, food security and ecosystem resilience’. PMID:28080985

A PR-1-like Protein of Fusarium oxysporum Functions in Virulence on Mammalian Hosts*

PubMed Central

Prados-Rosales, Rafael C.; Roldán-Rodríguez, Raquel; Serena, Carolina; López-Berges, Manuel S.; Guarro, Josep; Martínez-del-Pozo, Álvaro; Di Pietro, Antonio

2012-01-01

The pathogenesis-related PR-1-like protein family comprises secreted proteins from the animal, plant, and fungal kingdoms whose biological function remains poorly understood. Here we have characterized a PR-1-like protein, Fpr1, from Fusarium oxysporum, an ubiquitous fungal pathogen that causes vascular wilt disease on a wide range of plant species and can produce life-threatening infections in immunocompromised humans. Fpr1 is secreted and proteolytically processed by the fungus. The fpr1 gene is required for virulence in a disseminated immunodepressed mouse model, and its function depends on the integrity of the proposed active site of PR-1-like proteins. Fpr1 belongs to a gene family that has expanded in plant pathogenic Sordariomycetes. These results suggest that secreted PR-1-like proteins play important roles in fungal pathogenicity. PMID:22553200

Phomalactone from a Phytopathogenic Fungus Infecting ZINNIA elegans (ASTERACEAE) Leaves.

PubMed

Meepagala, Kumudini M; Johnson, Robert D; Techen, Natascha; Wedge, David E; Duke, Stephen O

2015-07-01

Zinnia elegans Jacq. plants are infected by a fungus that causes dark red spots with necrosis on leaves, particularly in late spring to the middle of summer in the Mid-South of the United States. This fungal disease causes the leaves to wilt and eventually kills the plant. The fungus was isolated, cultured in potato dextrose broth, and identified as Nigrospora sphaerica by molecular techniques. Two major lactone metabolites (phomalactone and catenioblin A) were isolated from liquid culture of N. sphaerica isolated from Z. elegans. When injected into leaves of Z. elegans, phomalactone caused lesions similar to those of the fungus. The lesion sizes were proportional to the concentration of the phomalactone. Phomalactone, but not catenioblin A, was phytotoxic to Z. elegans and other plant species by inhibition of seedling growth and by causing electrolyte leakage from photosynthetic tissues of both Z. elegans leaves and cucumber cotyledons. This latter effect may be related to the wilting caused by the fungus in mature Z. elegans plants. Phomalactone was moderately fungicidal to Coletotrichum fragariae and two Phomopsis species, indicating that the compound may keep certain other fungi from encroaching into plant tissue that N. sphaerica has infected. Production of large amounts of phomalactone by N. sphaerica contributes to the pathogenic behavior of this fungus, and may have other ecological functions in the interaction of N. sphaerica with other fungi. This is the first report of isolation of catenioblin A from a plant pathogenic fungus. The function of catenioblin A is unclear, as it was neither significantly phyto- nor fungitoxic.

The type III secretion system is necessary for the development of a pathogenic and endophytic interaction between Herbaspirillum rubrisubalbicans and Poaceae.

PubMed

Schmidt, Maria Augusta; Balsanelli, Eduardo; Faoro, Hellison; Cruz, Leonardo M; Wassem, Roseli; de Baura, Valter A; Weiss, Vinícius; Yates, Marshall G; Madeira, Humberto M F; Pereira-Ferrari, Lilian; Fungaro, Maria H P; de Paula, Francine M; Pereira, Luiz F P; Vieira, Luiz G E; Olivares, Fábio L; Pedrosa, Fábio O; de Souza, Emanuel M; Monteiro, Rose A

2012-06-06

Herbaspirillum rubrisubalbicans was first identified as a bacterial plant pathogen, causing the mottled stripe disease in sugarcane. H. rubrisubalbicans can also associate with various plants of economic interest in a non pathogenic manner. A 21 kb DNA region of the H. rubrisubalbicans genome contains a cluster of 26 hrp/hrc genes encoding for the type three secretion system (T3SS) proteins. To investigate the contribution of T3SS to the plant-bacterial interaction process we generated mutant strains of H. rubrisubalbicans M1 carrying a Tn5 insertion in both the hrcN and hrpE genes. H. rubrisulbalbicans hrpE and hrcN mutant strains of the T3SS system failed to cause the mottled stripe disease in the sugarcane susceptible variety B-4362. These mutant strains also did not produce lesions on Vigna unguiculata leaves. Oryza sativa and Zea mays colonization experiments showed that mutations in hrpE and hrcN genes reduced the capacity of H. rubrisulbalbicans to colonize these plants, suggesting that hrpE and hrcN genes are involved in the endophytic colonization. Our results indicate that the T3SS of H. rubrisubalbicans is necessary for the development of the mottled stripe disease and endophytic colonization of rice.

Genomic dissection of host-microbe and microbe-microbe interactions for advanced plant breeding.

PubMed

Kroll, Samuel; Agler, Matthew T; Kemen, Eric

2017-04-01

Agriculture faces many emerging challenges to sustainability, including limited nutrient resources, losses from diseases caused by current and emerging pathogens and environmental degradation. Microorganisms have great importance for plant growth and performance, including the potential to increase yields, nutrient uptake and pathogen resistance. An urgent need is therefore to understand and engineer plants and their associated microbial communities. Recent massive genomic sequencing of host plants and associated microbes offers resources to identify novel mechanisms of communal assembly mediated by the host. For example, host-microbe and microbe-microbe interactions are involved in niche formation, thereby contributing to colonization. By leveraging genomic resources, genetic traits underlying those mechanisms will become important resources to design plants selecting and hosting beneficial microbial communities. Copyright © 2017 Elsevier Ltd. All rights reserved.

The fire blight pathogen Erwinia amylovora requires the rpoN gene for pathogenicity in apple.

PubMed

Ramos, Laura S; Lehman, Brian L; Sinn, Judith P; Pfeufer, Emily E; Halbrendt, Noemi O; McNellis, Timothy W

2013-10-01

RpoN is a σ(54) factor regulating essential virulence gene expression in several plant pathogenic bacteria, including Pseudomonas syringae and Pectobacterium carotovorum. In this study, we found that mutation of rpoN in the fire blight pathogen Erwinia amylovora caused a nonpathogenic phenotype. The E. amylovora rpoN Tn5 transposon mutant rpoN1250::Tn5 did not cause fire blight disease symptoms on shoots of mature apple trees. In detached immature apple fruits, the rpoN1250::Tn5 mutant failed to cause fire blight disease symptoms and grew to population levels 12 orders of magnitude lower than the wild-type. In addition, the rpoN1250::Tn5 mutant failed to elicit a hypersensitive response when infiltrated into nonhost tobacco plant leaves, and rpoN1250::Tn5 cells failed to express HrpN protein when grown in hrp (hypersensitive response and pathogenicity)-inducing liquid medium. A plasmid-borne copy of the wild-type rpoN gene complemented all the rpoN1250::Tn5 mutant phenotypes tested. The rpoN1250::Tn5 mutant was prototrophic on minimal solid and liquid media, indicating that the rpoN1250::Tn5 nonpathogenic phenotype was not caused by a defect in basic metabolism or growth. This study provides clear genetic evidence that rpoN is an essential virulence gene of E. amylovora, suggesting that rpoN has the same function in E. amylovora as in P. syringae and Pe. carotovorum. 2013 BSPP and JOHN WILEY & SONS LTD

The Sugarcane Defense Protein SUGARWIN2 Causes Cell Death in Colletotrichum falcatum but Not in Non-Pathogenic Fungi

PubMed Central

Franco, Flávia P.; Santiago, Adelita C.; Henrique-Silva, Flávio; de Castro, Patrícia Alves; Goldman, Gustavo H.; Moura, Daniel S.; Silva-Filho, Marcio C.

2014-01-01

Plants respond to pathogens and insect attacks by inducing and accumulating a large set of defense-related proteins. Two homologues of a barley wound-inducible protein (BARWIN) have been characterized in sugarcane, SUGARWIN1 and SUGARWIN2 (sugarcane wound-inducible proteins). Induction of SUGARWINs occurs in response to Diatraea saccharalis damage but not to pathogen infection. In addition, the protein itself does not show any effect on insect development; instead, it has antimicrobial activities toward Fusarium verticillioides, an opportunistic fungus that usually occurs after D. saccharalis borer attacks on sugarcane. In this study, we sought to evaluate the specificity of SUGARWIN2 to better understand its mechanism of action against phytopathogens and the associations between fungi and insects that affect plants. We used Colletotrichum falcatum, a fungus that causes red rot disease in sugarcane fields infested by D. saccharalis, and Ceratocystis paradoxa, which causes pineapple disease in sugarcane. We also tested whether SUGARWIN2 is able to cause cell death in Aspergillus nidulans, a fungus that does not infect sugarcane, and in the model yeast Saccharomyces cerevisiae, which is used for bioethanol production. Recombinant SUGARWIN2 altered C. falcatum morphology by increasing vacuolization, points of fractures and a leak of intracellular material, leading to germling apoptosis. In C. paradoxa, SUGARWIN2 showed increased vacuolization in hyphae but did not kill the fungi. Neither the non-pathogenic fungus A. nidulans nor the yeast S. cerevisiae was affected by recombinant SUGARWIN2, suggesting that the protein is specific to sugarcane opportunistic fungal pathogens. PMID:24608349

Is the pathogenic ergot fungus a conditional defensive mutualist for its host grass?

PubMed

Wäli, Pauliina P; Wäli, Piippa R; Saikkonen, Kari; Tuomi, Juha

2013-01-01

It is well recognized, that outcomes of mutualistic plant-microorganism interactions are often context dependent and can range from mutualistic to antagonistic depending on conditions. Instead, seemingly pathogenic associations are generally considered only harmful to plants. The ergot fungus (Claviceps purpurea) is a common seed pathogen of grasses and cereals. Ergot sclerotia contain alkaloids which can cause severe toxicity in mammals when ingested, and thus the fungal infection might provide protection for the host plant against mammalian herbivores. Theoretically, the net effect of ergot infection would positively affect host seed set if the cost is not too high and the defensive effect is strong enough. According to our empirical data, this situation is plausible. First, we found no statistically significant seed loss in wild red fescue (Festuca rubra) inflorescences due to ergot infection, but the seed succession decreased along increasing number of sclerotia. Second, in a food choice experiment, sheep showed avoidance against forage containing ergot. Third, the frequency of ergot-infected inflorescences was higher in sheep pastures than surrounding ungrazed areas, indicating a protective effect against mammalian grazing. We conclude that, although ergot can primarily be categorized as a plant pathogen, ergot infection may sometimes represent indirect beneficial effects for the host plant. Ergot may thus serve as a conditional defensive mutualist for its host grass, and the pathogenic interaction may range from antagonistic to mutualistic depending on the situation.

Is the Pathogenic Ergot Fungus a Conditional Defensive Mutualist for Its Host Grass?

PubMed Central

Wäli, Pauliina P.; Wäli, Piippa R.; Saikkonen, Kari; Tuomi, Juha

2013-01-01

It is well recognized, that outcomes of mutualistic plant-microorganism interactions are often context dependent and can range from mutualistic to antagonistic depending on conditions. Instead, seemingly pathogenic associations are generally considered only harmful to plants. The ergot fungus (Claviceps purpurea) is a common seed pathogen of grasses and cereals. Ergot sclerotia contain alkaloids which can cause severe toxicity in mammals when ingested, and thus the fungal infection might provide protection for the host plant against mammalian herbivores. Theoretically, the net effect of ergot infection would positively affect host seed set if the cost is not too high and the defensive effect is strong enough. According to our empirical data, this situation is plausible. First, we found no statistically significant seed loss in wild red fescue (Festuca rubra) inflorescences due to ergot infection, but the seed succession decreased along increasing number of sclerotia. Second, in a food choice experiment, sheep showed avoidance against forage containing ergot. Third, the frequency of ergot-infected inflorescences was higher in sheep pastures than surrounding ungrazed areas, indicating a protective effect against mammalian grazing. We conclude that, although ergot can primarily be categorized as a plant pathogen, ergot infection may sometimes represent indirect beneficial effects for the host plant. Ergot may thus serve as a conditional defensive mutualist for its host grass, and the pathogenic interaction may range from antagonistic to mutualistic depending on the situation. PMID:23874924

The Lr34 adult plant rust resistance gene provides seedling resistance in durum wheat without senescence.

PubMed

Rinaldo, Amy; Gilbert, Brian; Boni, Rainer; Krattinger, Simon G; Singh, Davinder; Park, Robert F; Lagudah, Evans; Ayliffe, Michael

2017-07-01

The hexaploid wheat (Triticum aestivum) adult plant resistance gene, Lr34/Yr18/Sr57/Pm38/Ltn1, provides broad-spectrum resistance to wheat leaf rust (Lr34), stripe rust (Yr18), stem rust (Sr57) and powdery mildew (Pm38) pathogens, and has remained effective in wheat crops for many decades. The partial resistance provided by this gene is only apparent in adult plants and not effective in field-grown seedlings. Lr34 also causes leaf tip necrosis (Ltn1) in mature adult plant leaves when grown under field conditions. This D genome-encoded bread wheat gene was transferred to tetraploid durum wheat (T. turgidum) cultivar Stewart by transformation. Transgenic durum lines were produced with elevated gene expression levels when compared with the endogenous hexaploid gene. Unlike nontransgenic hexaploid and durum control lines, these transgenic plants showed robust seedling resistance to pathogens causing wheat leaf rust, stripe rust and powdery mildew disease. The effectiveness of seedling resistance against each pathogen correlated with the level of transgene expression. No evidence of accelerated leaf necrosis or up-regulation of senescence gene markers was apparent in these seedlings, suggesting senescence is not required for Lr34 resistance, although leaf tip necrosis occurred in mature plant flag leaves. Several abiotic stress-response genes were up-regulated in these seedlings in the absence of rust infection as previously observed in adult plant flag leaves of hexaploid wheat. Increasing day length significantly increased Lr34 seedling resistance. These data demonstrate that expression of a highly durable, broad-spectrum adult plant resistance gene can be modified to provide seedling resistance in durum wheat. © 2016 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd.

Conserved nematode signaling molecules elicit plant defenses and pathogen resistance

USDA-ARS?s Scientific Manuscript database

Nematodes, which are ubiquitous in soil and are estimated to cause $100 B of agricultural damage annually, produce novel, highly conserved small sugar-based molecules call ascarosides. Ascarosides play critical roles in nematode development and behavior. We report here that plants recognize these un...

A molecular tug-of-war: Global plant proteome changes during viral infection

USDA-ARS?s Scientific Manuscript database

Plant pathogenic viruses cause a number of economically important diseases in food, fuel, and fiber crops worldwide. As obligate parasites with highly reduced genomes, viruses rely heavily on their hosts for replication, assembly, intra- and intercellular movement, and attraction of vectors for disp...

Putative rust fungal effector proteins in infected bean and soybean leaves

USDA-ARS?s Scientific Manuscript database

The plant pathogenic fungi Uromyces appendiculatus and Phakopsora pachyrhizi cause debilitating rust diseases on common bean and soybean. These rust fungi secrete effector proteins that allow them to infect plants, but the effector repertoire for U. appendiculatus and P. pachyrhizi is not fully def...

The Bacterial Pathogen Xylella fastidiosa Affects the Leaf Ionome of Plant Hosts during Infection

PubMed Central

De La Fuente, Leonardo; Parker, Jennifer K.; Oliver, Jonathan E.; Granger, Shea; Brannen, Phillip M.; van Santen, Edzard; Cobine, Paul A.

2013-01-01

Xylella fastidiosa is a plant pathogenic bacterium that lives inside the host xylem vessels, where it forms biofilm believed to be responsible for disrupting the passage of water and nutrients. Here, Nicotiana tabacum was infected with X. fastidiosa, and the spatial and temporal changes in the whole-leaf ionome (i.e. the mineral and trace element composition) were measured as the host plant transitioned from healthy to diseased physiological status. The elemental composition of leaves was used as an indicator of the physiological changes in the host at a specific time and relative position during plant development. Bacterial infection was found to cause significant increases in concentrations of calcium prior to the appearance of symptoms and decreases in concentrations of phosphorous after symptoms appeared. Field-collected leaves from multiple varieties of grape, blueberry, and pecan plants grown in different locations over a four-year period in the Southeastern US showed the same alterations in Ca and P. This descriptive ionomics approach characterizes the existence of a mineral element-based response to X. fastidiosa using a model system suitable for further manipulation to uncover additional details of the role of mineral elements during plant-pathogen interactions. This is the first report on the dynamics of changes in the ionome of the host plant throughout the process of infection by a pathogen. PMID:23667547

Enhanced resistance in Theobroma cacao against oomycete and fungal pathogens by secretion of phosphatidylinositol-3-phosphate-binding proteins.

PubMed

Helliwell, Emily E; Vega-Arreguín, Julio; Shi, Zi; Bailey, Bryan; Xiao, Shunyuan; Maximova, Siela N; Tyler, Brett M; Guiltinan, Mark J

2016-03-01

The internalization of some oomycete and fungal pathogen effectors into host plant cells has been reported to be blocked by proteins that bind to the effectors' cell entry receptor, phosphatidylinositol-3-phosphate (PI3P). This finding suggested a novel strategy for disease control by engineering plants to secrete PI3P-binding proteins. In this study, we tested this strategy using the chocolate tree Theobroma cacao. Transient expression and secretion of four different PI3P-binding proteins in detached leaves of T. cacao greatly reduced infection by two oomycete pathogens, Phytophthora tropicalis and Phytophthora palmivora, which cause black pod disease. Lesion size and pathogen growth were reduced by up to 85%. Resistance was not conferred by proteins lacking a secretory leader, by proteins with mutations in their PI3P-binding site, or by a secreted PI4P-binding protein. Stably transformed, transgenic T. cacao plants expressing two different PI3P-binding proteins showed substantially enhanced resistance to both P. tropicalis and P. palmivora, as well as to the fungal pathogen Colletotrichum theobromicola. These results demonstrate that secretion of PI3P-binding proteins is an effective way to increase disease resistance in T. cacao, and potentially in other plants, against a broad spectrum of pathogens. © 2015 Society for Experimental Biology, Association of Applied Biologists and John Wiley & Sons Ltd.

Studies on oil palm trunks as sources of infection in the field.

PubMed

Flood, J; Keenan, L; Wayne, S; Hasan, Y

2005-01-01

Diseases of oil palm caused by Ganoderma boninense are of major economic importance in much of South-East Asia. This paper describes results from an ongoing field trial concerning the spread of the pathogen from artificially inoculated trunks used to simulate spread from windrowed trunks. Three planting distances for bait seedlings revealed that the closer the seedling was planted to the source of inoculum the sooner it succumbed to the disease. However, infection only occurred when the trunks were mounded (covered with soil), and seedlings planted around uncovered trunks (at any distance) have showed no symptoms of disease to date. Isolates are being collected from infected plants and molecular analysis is being undertaken to give more information on the spread of the pathogen.

Antioxidant genes of plants and fungal pathogens are distinctly regulated during disease development in different Rhizoctonia solani pathosystems.

PubMed

Samsatly, Jamil; Copley, Tanya R; Jabaji, Suha H

2018-01-01

Biotic stress, as a result of plant-pathogen interactions, induces the accumulation of reactive oxygen species in the cells, causing severe oxidative damage to plants and pathogens. To overcome this damage, both the host and pathogen have developed antioxidant systems to quench excess ROS and keep ROS production and scavenging systems under control. Data on ROS-scavenging systems in the necrotrophic plant pathogen Rhizoctonia solani are just emerging. We formerly identified vitamin B6 biosynthetic machinery of R. solani AG3 as a powerful antioxidant exhibiting a high ability to quench ROS, similar to CATALASE (CAT) and GLUTATHIONE S-TRANSFERASE (GST). Here, we provide evidence on the involvement of R. solani vitamin B6 biosynthetic pathway genes; RsolPDX1 (KF620111.1), RsolPDX2 (KF620112.1), and RsolPLR (KJ395592.1) in vitamin B6 de novo biosynthesis by yeast complementation assays. Since gene expression studies focusing on oxidative stress responses of both the plant and the pathogen following R. solani infection are very limited, this study is the first coexpression analysis of genes encoding vitamin B6, CAT and GST in plant and fungal tissues of three pathosystems during interaction of different AG groups of R. solani with their respective hosts. The findings indicate that distinct expression patterns of fungal and host antioxidant genes were correlated in necrotic tissues and their surrounding areas in each of the three R. solani pathosystems: potato sprout-R. solani AG3; soybean hypocotyl-R. solani AG4 and soybean leaves-R. solani AG1-IA interactions. Levels of ROS increased in all types of potato and soybean tissues, and in fungal hyphae following infection of R. solani AGs as determined by non-fluorescence and fluorescence methods using H2DCF-DA and DAB, respectively. Overall, we demonstrate that the co-expression and accumulation of certain plant and pathogen ROS-antioxidant related genes in each pathosystem are highlighted and might be critical during disease development from the plant's point of view, and in pathogenicity and developing of infection structures from the fungal point of view.

A comparative hidden Markov model analysis pipeline identifies proteins characteristic of cereal-infecting fungi

PubMed Central

2013-01-01

Background Fungal pathogens cause devastating losses in economically important cereal crops by utilising pathogen proteins to infect host plants. Secreted pathogen proteins are referred to as effectors and have thus far been identified by selecting small, cysteine-rich peptides from the secretome despite increasing evidence that not all effectors share these attributes. Results We take advantage of the availability of sequenced fungal genomes and present an unbiased method for finding putative pathogen proteins and secreted effectors in a query genome via comparative hidden Markov model analyses followed by unsupervised protein clustering. Our method returns experimentally validated fungal effectors in Stagonospora nodorum and Fusarium oxysporum as well as the N-terminal Y/F/WxC-motif from the barley powdery mildew pathogen. Application to the cereal pathogen Fusarium graminearum reveals a secreted phosphorylcholine phosphatase that is characteristic of hemibiotrophic and necrotrophic cereal pathogens and shares an ancient selection process with bacterial plant pathogens. Three F. graminearum protein clusters are found with an enriched secretion signal. One of these putative effector clusters contains proteins that share a [SG]-P-C-[KR]-P sequence motif in the N-terminal and show features not commonly associated with fungal effectors. This motif is conserved in secreted pathogenic Fusarium proteins and a prime candidate for functional testing. Conclusions Our pipeline has successfully uncovered conservation patterns, putative effectors and motifs of fungal pathogens that would have been overlooked by existing approaches that identify effectors as small, secreted, cysteine-rich peptides. It can be applied to any pathogenic proteome data, such as microbial pathogen data of plants and other organisms. PMID:24252298

Colonization of plants by human pathogenic bacteria in the course of organic vegetable production.

PubMed

Hofmann, Andreas; Fischer, Doreen; Hartmann, Anton; Schmid, Michael

2014-01-01

In recent years, increasing numbers of outbreaks caused by the consumption of vegetables contaminated with human pathogenic bacteria were reported. The application of organic fertilizers during vegetable production is one of the possible reasons for contamination with those pathogens. In this study laboratory experiments in axenic and soil systems following common practices in organic farming were conducted to identify the minimal dose needed for bacterial colonization of plants and to identify possible factors like bacterial species or serovariation, plant species or organic fertilizer types used, influencing the success of plant colonization by human pathogenic bacteria. Spinach and corn salad were chosen as model plants and were inoculated with different concentrations of Salmonella enterica sv. Weltevreden, Listeria monocytogenes sv. 4b and EGD-E sv. 1/2a either directly (axenic system) or via agricultural soil amended with spiked organic fertilizers (soil system). In addition to PCR- and culture-based detection methods, fluorescence in situ hybridization (FISH) was applied in order to localize bacteria on or in plant tissues. Our results demonstrate that shoots were colonized by the pathogenic bacteria at inoculation doses as low as 4 × 10 CFU/ml in the axenic system or 4 × 10(5) CFU/g in the soil system. In addition, plant species dependent effects were observed. Spinach was colonized more often and at lower inoculation doses compared to corn salad. Differential colonization sites on roots, depending on the plant species could be detected using FISH-CLSM analysis. Furthermore, the transfer of pathogenic bacteria to plants via organic fertilizers was observed more often and at lower initial inoculation doses when fertilization was performed with inoculated slurry compared to inoculated manure. Finally, it could be shown that by introducing a simple washing step, the bacterial contamination was reduced in most cases or even was removed completely in some cases.

Colonization of plants by human pathogenic bacteria in the course of organic vegetable production

PubMed Central

Hofmann, Andreas; Fischer, Doreen; Hartmann, Anton; Schmid, Michael

2014-01-01

In recent years, increasing numbers of outbreaks caused by the consumption of vegetables contaminated with human pathogenic bacteria were reported. The application of organic fertilizers during vegetable production is one of the possible reasons for contamination with those pathogens. In this study laboratory experiments in axenic and soil systems following common practices in organic farming were conducted to identify the minimal dose needed for bacterial colonization of plants and to identify possible factors like bacterial species or serovariation, plant species or organic fertilizer types used, influencing the success of plant colonization by human pathogenic bacteria. Spinach and corn salad were chosen as model plants and were inoculated with different concentrations of Salmonella enterica sv. Weltevreden, Listeria monocytogenes sv. 4b and EGD-E sv. 1/2a either directly (axenic system) or via agricultural soil amended with spiked organic fertilizers (soil system). In addition to PCR- and culture-based detection methods, fluorescence in situ hybridization (FISH) was applied in order to localize bacteria on or in plant tissues. Our results demonstrate that shoots were colonized by the pathogenic bacteria at inoculation doses as low as 4 × 10 CFU/ml in the axenic system or 4 × 105 CFU/g in the soil system. In addition, plant species dependent effects were observed. Spinach was colonized more often and at lower inoculation doses compared to corn salad. Differential colonization sites on roots, depending on the plant species could be detected using FISH-CLSM analysis. Furthermore, the transfer of pathogenic bacteria to plants via organic fertilizers was observed more often and at lower initial inoculation doses when fertilization was performed with inoculated slurry compared to inoculated manure. Finally, it could be shown that by introducing a simple washing step, the bacterial contamination was reduced in most cases or even was removed completely in some cases. PMID:24829562

The CebE/MsiK Transporter is a Doorway to the Cello-oligosaccharide-mediated Induction of Streptomyces scabies Pathogenicity

PubMed Central

Jourdan, Samuel; Francis, Isolde Maria; Kim, Min Jung; Salazar, Joren Jeico C.; Planckaert, Sören; Frère, Jean-Marie; Matagne, André; Kerff, Frédéric; Devreese, Bart; Loria, Rosemary; Rigali, Sébastien

2016-01-01

Streptomyces scabies is an economically important plant pathogen well-known for damaging root and tuber crops by causing scab lesions. Thaxtomin A is the main causative agent responsible for the pathogenicity of S. scabies and cello-oligosaccharides are environmental triggers that induce the production of this phytotoxin. How cello-oligosaccharides are sensed or transported in order to induce the virulent behavior of S. scabies? Here we report that the cellobiose and cellotriose binding protein CebE, and MsiK, the ATPase providing energy for carbohydrates transport, are the protagonists of the cello-oligosaccharide mediated induction of thaxtomin production in S. scabies. Our work provides the first example where the transport and not the sensing of major constituents of the plant host is the central mechanism associated with virulence of the pathogen. Our results allow to draw a complete pathway from signal transport to phytotoxin production where each step of the cascade is controlled by CebR, the cellulose utilization regulator. We propose the high affinity of CebE to cellotriose as possible adaptation of S. scabies to colonize expanding plant tissue. Our work further highlights how genes associated with primary metabolism in nonpathogenic Streptomyces species have been recruited as basic elements of virulence in plant pathogenic species. PMID:27250236

Gene expression profile of the plant pathogen Fusarium graminearum under the antagonistic effect of Pantoea agglomerans.

PubMed

Pandolfi, V; Jorge, E C; Melo, C M R; Albuquerque, A C S; Carrer, H

2010-07-06

The pathogenic fungus Fusarium graminearum is an ongoing threat to agriculture, causing losses in grain yield and quality in diverse crops. Substantial progress has been made in the identification of genes involved in the suppression of phytopathogens by antagonistic microorganisms; however, limited information regarding responses of plant pathogens to these biocontrol agents is available. Gene expression analysis was used to identify differentially expressed transcripts of the fungal plant pathogen F. graminearum under antagonistic effect of the bacterium Pantoea agglomerans. A macroarray was constructed, using 1014 transcripts from an F. graminearum cDNA library. Probes consisted of the cDNA of F. graminearum grown in the presence and in the absence of P. agglomerans. Twenty-nine genes were either up (19) or down (10) regulated during interaction with the antagonist bacterium. Genes encoding proteins associated with fungal defense and/or virulence or with nutritional and oxidative stress responses were induced. The repressed genes coded for a zinc finger protein associated with cell division, proteins containing cellular signaling domains, respiratory chain proteins, and chaperone-type proteins. These data give molecular and biochemical evidence of response of F. graminearum to an antagonist and could help develop effective biocontrol procedures for pathogenic plant fungi.

New report of additional enterobacterial species causing wilt in West Bengal, India.

PubMed

Sarkar, Shamayeeta; Chaudhuri, Sujata

2015-07-01

Ralstonia solanacearum is known to be the most prominent causal agent of bacterial wilt worldwide. It has a wide host range comprising solanaceous and nonsolanaceous plants. Typical symptoms of the disease are leaf wilt, browning of vascular tissues, and collapsing of the plant. With the objective of studying the diversity of pathogens causing bacterial wilt in West Bengal, we collected samples of diseased symptomatic crops and adjacent symptomatic and asymptomatic weeds from widespread locations in West Bengal. By means of a routine molecular identification test specific to "R. solanacearum species complex", the majority of these strains (68 out of 71) were found to not be R. solanacearum. Presumptive identification of these isolates with conventional biochemicals, extensive testing of pathogenicity of a subset involving greenhouse trials fulfilling Koch's postulate test, and scanning electron microscopic analysis for the presence of pathogen in diseased plants were done. 16S rDNA sequencing of a subset of these strains (GenBank accession Nos. JX880249-JX880251) and analysis of sequences with the nBLAST programme showed a high similarity (97%-99%) to sequences of the Enterobacteriaceae group available in GenBank. Molecular phylogeny further established the taxonomic position of the strains. The 3 bacterial strain cultures have been submitted to MTCC, Institute of Microbial Technology, Chandigarh, India, and were identified as Klebsiella oxytoca, Enterobacter cowanii, and Klebsiella oxytoca, respectively. Although Enterobacter sp. has previously been reported to cause wilt in many plants, susceptibility of most of the dedicated hosts of R. solanacearum to wilt caused by Enterobacter and other bacteria from Enterobacteriaceae is being reported for the first time in this work.

Aggressive root pathogen Phellinus noxius and implications for western Pacific Islands

Treesearch

Sara M. Ashiglar; Phil G. Cannon; Ned B. Klopfenstein

2015-01-01

Phellinus noxius is an aggressive root rot pathogen affecting tropical and subtropical forests. Causing much damage in tropical Asia, Africa, Taiwan, Japan and the Pacific Islands, its wide host range encompasses more than 200 plant species representing 59 families (Ann et al. 2002). It can devastate agricultural plantations of tea, rubber, cocoa, avocados,...

Transcriptome analyses suggest a disturbance of iron homeostasis in soybean leaves during white mould disease establishment

USDA-ARS?s Scientific Manuscript database

Sclerotinia sclerotiorum is a serious pathogen of numerous crops around the world. The major virulence factor of this pathogen is oxalic acid (OA). Mutants that cannot produce OA do not cause disease, and plants that express enzymes that degrade OA, such as oxalate oxidase (OxO) are very resistant t...

Comparative Susceptibility of Plants Native to the Appalachian Range of the United States to Inoculation With Phytophthora ramorum

Treesearch

R.G. Linderman; Patricia B. de Sá; E.A. Davis

2008-01-01

Phytophthora ramorum, cause of sudden oak death of trees or ramorum blight of other plant species, has many hosts. Some geographic regions, such as the Appalachian range of the eastern United States, are considered high risk of becoming infested with the pathogen because known susceptible plants occur there and climatic characteristics appear...

Higher plant diversity promotes higher diversity of fungal pathogens, while it decreases pathogen infection per plant.

PubMed

Rottstock, Tanja; Joshi, Jasmin; Kummer, Volker; Fischer, Markus

2014-07-01

Fungal plant pathogens are common in natural communities where they affect plant physiology, plant survival, and biomass production. Conversely, pathogen transmission and infection may be regulated by plant community characteristics such as plant species diversity and functional composition that favor pathogen diversity through increases in host diversity while simultaneously reducing pathogen infection via increased variability in host density and spatial heterogeneity. Therefore, a comprehensive understanding of multi-host multi-pathogen interactions is of high significance in the context of biodiversity-ecosystem functioning. We investigated the relationship between plant diversity and aboveground obligate parasitic fungal pathogen ("pathogens" hereafter) diversity and infection in grasslands of a long-term, large-scale, biodiversity experiment with varying plant species (1-60 species) and plant functional group diversity (1-4 groups). To estimate pathogen infection of the plant communities, we visually assessed pathogen-group presence (i.e., rusts, powdery mildews, downy mildews, smuts, and leaf-spot diseases) and overall infection levels (combining incidence and severity of each pathogen group) in 82 experimental plots on all aboveground organs of all plant species per plot during four surveys in 2006. Pathogen diversity, assessed as the cumulative number of pathogen groups on all plant species per plot, increased log-linearly with plant species diversity. However, pathogen incidence and severity, and hence overall infection, decreased with increasing plant species diversity. In addition, co-infection of plant individuals by two or more pathogen groups was less likely with increasing plant community diversity. We conclude that plant community diversity promotes pathogen-community diversity while at the same time reducing pathogen infection levels of plant individuals.

Profile and Fate of Bacterial Pathogens in Sewage Treatment Plants Revealed by High-Throughput Metagenomic Approach.

PubMed

Li, Bing; Ju, Feng; Cai, Lin; Zhang, Tong

2015-09-01

The broad-spectrum profile of bacterial pathogens and their fate in sewage treatment plants (STPs) were investigated using high-throughput sequencing based metagenomic approach. This novel approach could provide a united platform to standardize bacterial pathogen detection and realize direct comparison among different samples. Totally, 113 bacterial pathogen species were detected in eight samples including influent, effluent, activated sludge (AS), biofilm, and anaerobic digestion sludge with the abundances ranging from 0.000095% to 4.89%. Among these 113 bacterial pathogens, 79 species were reported in STPs for the first time. Specially, compared to AS in bulk mixed liquor, more pathogen species and higher total abundance were detected in upper foaming layer of AS. This suggests that the foaming layer of AS might impose more threat to onsite workers and citizens in the surrounding areas of STPs because pathogens in foaming layer are easily transferred into air and cause possible infections. The high removal efficiency (98.0%) of total bacterial pathogens suggests that AS treatment process is effective to remove most bacterial pathogens. Remarkable similarities of bacterial pathogen compositions between influent and human gut indicated that bacterial pathogen profiles in influents could well reflect the average bacterial pathogen communities of urban resident guts within the STP catchment area.

Rice Blast Fungus (Magnaporthe oryzae) Infects Arabidopsis via a Mechanism Distinct from That Required for the Infection of Rice1[W][OA

PubMed Central

Park, Ju-Young; Jin, Jianming; Lee, Yin-Won; Kang, Seogchan; Lee, Yong-Hwan

2009-01-01

Magnaporthe oryzae is a hemibiotrophic fungal pathogen that causes rice (Oryza sativa) blast. Although M. oryzae as a whole infects a wide variety of monocotyledonous hosts, no dicotyledonous plant has been reported as a host. We found that two rice pathogenic strains of M. oryzae, KJ201 and 70-15, interacted differentially with 16 ecotypes of Arabidopsis (Arabidopsis thaliana). Strain KJ201 infected all ecotypes with varying degrees of virulence, whereas strain 70-15 caused no symptoms in certain ecotypes. In highly susceptible ecotypes, small chlorotic lesions appeared on infected leaves within 3 d after inoculation and subsequently expanded across the affected leaves. The fungus produced spores in susceptible ecotypes but not in resistant ecotypes. Fungal cultures recovered from necrotic lesions caused the same symptoms in healthy plants, satisfying Koch's postulates. Histochemical analyses showed that infection by the fungus caused an accumulation of reactive oxygen species and eventual cell death. Similar to the infection process in rice, the fungus differentiated to form appressorium and directly penetrated the leaf surface in Arabidopsis. However, the pathogenic mechanism in Arabidopsis appears distinct from that in rice; three fungal genes essential for pathogenicity in rice played only limited roles in causing disease symptoms in Arabidopsis, and the fungus seems to colonize Arabidopsis as a necrotroph through the secretion of phytotoxic compounds, including 9,12-octadecadienoic acid. Expression of PR-1 and PDF1.2 was induced in response to infection by the fungus, suggesting the activation of salicylic acid- and jasmonic acid/ethylene-dependent signaling pathways. However, the roles of these signaling pathways in defense against M. oryzae remain unclear. In combination with the wealth of genetic and genomic resources available for M. oryzae, this newly established pathosystem allows comparison of the molecular and cellular mechanisms underlying pathogenesis and host defense in two well-studied model plants. PMID:18987215

Complete genome sequence of the plant pathogen Erwinia amylovora strain ATCC 49946

USDA-ARS?s Scientific Manuscript database

Erwinia amylovora causes the economically important disease fire blight that affects rosaceous plants, especially pear and apple. Here we report the complete genome sequence and annotation of strain ATCC 49946. The analysis of the sequence and its comparison with sequenced genomes of closely related...

Host plant affects morphometric variation of Diaphorina citri (Hemiptera: Liviidae)

USDA-ARS?s Scientific Manuscript database

The Asian citrus psyllid (ACP), due to its potential to vector the pathogen causing citrus greening disease or huanglongbing, is one of the most serious citrus pests worldwide. While optimal plant cultivars for ACP oviposition and development have been determined, little is known of the influence of...

Sharka epidemiology and worldwide management strategies: learning lessons to optimize disease control in perennial plants

USDA-ARS?s Scientific Manuscript database

Many plant epidemics that cause major economic losses cannot be controlled with pesticides. Among them, sharka epidemics severely affect prunus trees worldwide. Its causal agent, Plum pox virus (PPV;, genus Potyvirus), has been classified as a quarantine pathogen in numerous countries. As a result, ...

Participation of chitin-binding peroxidase isoforms in the wilt pathogenesis of cotton

USDA-ARS?s Scientific Manuscript database

Specific chitin-binding isozymes of peroxidase (POX) play an important role in pathogenesis of plant diseases caused with fungi. We studied the dynamics of peroxidase activity in two varieties of cotton (Gossypium hirsutum L.); one was a susceptible and the other resistant to the plant pathogen Vert...

Impact of hormonal crosstalk on plant resistance and fitness under multi-attacker conditions

PubMed Central

Vos, Irene A.; Moritz, Liselotte; Pieterse, Corné M. J.; Van Wees, Saskia C. M.

2015-01-01

The hormone salicylic acid (SA) generally induces plant defenses against biotrophic pathogens. Jasmonic acid (JA) and its oxylipin derivatives together with ethylene (ET) are generally important hormonal regulators of induced plant defenses against necrotrophic pathogens, whereas JAs together with abscisic acid (ABA) are implicated in induced plant defenses against herbivorous insects. Hormonal crosstalk between the different plant defense pathways has often been hypothesized to be a cost-saving strategy that has evolved as a means of the plant to reduce allocation costs by repression of unnecessary defenses, thereby minimizing trade-offs between plant defense and growth. However, proof for this hypothesis has not been demonstrated yet. In this study the impact of hormonal crosstalk on disease resistance and fitness of Arabidopsis thaliana when under multi-species attack was investigated. Induction of SA- or JA/ABA-dependent defense responses by the biotrophic pathogen Hyaloperonospora arabidopsidis or the herbivorous insect Pieris rapae, respectively, was shown to reduce the level of induced JA/ET-dependent defense against subsequent infection with the necrotrophic pathogen Botrytis cinerea. However, despite the enhanced susceptibility to this second attacker, no additional long-term negative effects were observed on plant fitness when plants had been challenged by multiple attackers. Similarly, when plants were grown in dense competition stands to enlarge fitness effects of induced defenses, treatment with a combination of SA and MeJA did not cause additional negative effects on plant fitness in comparison to the single MeJA treatment. Together, these data support the notion that hormonal crosstalk in plants during multi-attacker interactions allows plants to prioritize their defenses, while limiting the fitness costs associated with induction of defenses. PMID:26347758

Protection of Arabidopsis thaliana against Leaf-Pathogenic Pseudomonas syringae by Sphingomonas Strains in a Controlled Model System ▿ †

PubMed Central

Innerebner, Gerd; Knief, Claudia; Vorholt, Julia A.

2011-01-01

Diverse bacterial taxa live in association with plants without causing deleterious effects. Previous analyses of phyllosphere communities revealed the predominance of few bacterial genera on healthy dicotyl plants, provoking the question of whether these commensals play a particular role in plant protection. Here, we tested two of them, Methylobacterium and Sphingomonas, with respect to their ability to diminish disease symptom formation and the proliferation of the foliar plant pathogen Pseudomonas syringae pv. tomato DC3000 on Arabidopsis thaliana. Plants were grown under gnotobiotic conditions in the absence or presence of the potential antagonists and then challenged with the pathogen. No effect of Methylobacterium strains on disease development was observed. However, members of the genus Sphingomonas showed a striking plant-protective effect by suppressing disease symptoms and diminishing pathogen growth. A survey of different Sphingomonas strains revealed that most plant isolates protected A. thaliana plants from developing severe disease symptoms. This was not true for Sphingomonas strains isolated from air, dust, or water, even when they reached cell densities in the phyllosphere comparable to those of the plant isolates. This suggests that plant protection is common among plant-colonizing Sphingomonas spp. but is not a general trait conserved within the genus Sphingomonas. The carbon source profiling of representative isolates revealed differences between protecting and nonprotecting strains, suggesting that substrate competition plays a role in plant protection by Sphingomonas. However, other mechanisms cannot be excluded at this time. In conclusion, the ability to protect plants as shown here in a model system may be an unexplored, common trait of indigenous Sphingomonas spp. and may be of relevance under natural conditions. PMID:21421777

Fungal Infection Induces Sex-Specific Transcriptional Changes and Alters Sexual Dimorphism in the Dioecious Plant Silene latifolia

PubMed Central

Zemp, Niklaus; Tavares, Raquel; Widmer, Alex

2015-01-01

Sexual dimorphism, including differences in morphology, behavior and physiology between females and males, is widespread in animals and plants and is shaped by gene expression differences between the sexes. Such expression differences may also underlie sex-specific responses of hosts to pathogen infections, most notably when pathogens induce partial sex reversal in infected hosts. The genetic changes associated with sex-specific responses to pathogen infections on the one hand, and sexual dimorphism on the other hand, remain poorly understood. The dioecious White Campion (Silene latifolia) displays sexual dimorphism in floral traits and infection with the smut fungus Micobrotryum lychnidis-dioicae induces a partial sex reversal in females. We find strong sex-specific responses to pathogen infection and reduced sexual dimorphism in infected S. latifolia. This provides a direct link between pathogen-mediated changes in sex-biased gene expression and altered sexual dimorphism in the host. Expression changes following infection affected mainly genes with male-biased expression in healthy plants. In females, these genes were up-regulated, leading to a masculinization of the transcriptome. In contrast, infection in males was associated with down-regulation of these genes, leading to a demasculinization of the transcriptome. To a lesser extent, genes with female-biased expression in healthy plants were also affected in opposite directions in the two sexes. These genes were overall down-regulated in females and up-regulated in males, causing, respectively, a defeminization in infected females and a feminization of the transcriptome in infected males. Our results reveal strong sex-specific responses to pathogen infection in a dioecious plant and provide a link between pathogen-induced changes in sex-biased gene expression and sexual dimorphism. PMID:26448481

Fungal Infection Induces Sex-Specific Transcriptional Changes and Alters Sexual Dimorphism in the Dioecious Plant Silene latifolia.

PubMed

Zemp, Niklaus; Tavares, Raquel; Widmer, Alex

2015-10-01

Sexual dimorphism, including differences in morphology, behavior and physiology between females and males, is widespread in animals and plants and is shaped by gene expression differences between the sexes. Such expression differences may also underlie sex-specific responses of hosts to pathogen infections, most notably when pathogens induce partial sex reversal in infected hosts. The genetic changes associated with sex-specific responses to pathogen infections on the one hand, and sexual dimorphism on the other hand, remain poorly understood. The dioecious White Campion (Silene latifolia) displays sexual dimorphism in floral traits and infection with the smut fungus Micobrotryum lychnidis-dioicae induces a partial sex reversal in females. We find strong sex-specific responses to pathogen infection and reduced sexual dimorphism in infected S. latifolia. This provides a direct link between pathogen-mediated changes in sex-biased gene expression and altered sexual dimorphism in the host. Expression changes following infection affected mainly genes with male-biased expression in healthy plants. In females, these genes were up-regulated, leading to a masculinization of the transcriptome. In contrast, infection in males was associated with down-regulation of these genes, leading to a demasculinization of the transcriptome. To a lesser extent, genes with female-biased expression in healthy plants were also affected in opposite directions in the two sexes. These genes were overall down-regulated in females and up-regulated in males, causing, respectively, a defeminization in infected females and a feminization of the transcriptome in infected males. Our results reveal strong sex-specific responses to pathogen infection in a dioecious plant and provide a link between pathogen-induced changes in sex-biased gene expression and sexual dimorphism.

Improvement of the fungal biocontrol agent Trichoderma atroviride to enhance both antagonism and induction of plant systemic disease resistance.

PubMed

Brunner, Kurt; Zeilinger, Susanne; Ciliento, Rosalia; Woo, Sheridian L; Lorito, Matteo; Kubicek, Christian P; Mach, Robert L

2005-07-01

Biocontrol agents generally do not perform well enough under field conditions to compete with chemical fungicides. We determined whether transgenic strain SJ3-4 of Trichoderma atroviride, which expresses the Aspergillus niger glucose oxidase-encoding gene, goxA, under a homologous chitinase (nag1) promoter had increased capabilities as a fungal biocontrol agent. The transgenic strain differed only slightly from the wild-type in sporulation or the growth rate. goxA expression occurred immediately after contact with the plant pathogen, and the glucose oxidase formed was secreted. SJ3-4 had significantly less N-acetylglucosaminidase and endochitinase activities than its nontransformed parent. Glucose oxidase-containing culture filtrates exhibited threefold-greater inhibition of germination of spores of Botrytis cinerea. The transgenic strain also more quickly overgrew and lysed the plant pathogens Rhizoctonia solani and Pythium ultimum. In planta, SJ3-4 had no detectable improved effect against low inoculum levels of these pathogens. Beans planted in heavily infested soil and treated with conidia of the transgenic Trichoderma strain germinated, but beans treated with wild-type spores did not germinate. SJ3-4 also was more effective in inducing systemic resistance in plants. Beans with SJ3-4 root protection were highly resistant to leaf lesions caused by the foliar pathogen B. cinerea. This work demonstrates that heterologous genes driven by pathogen-inducible promoters can increase the biocontrol and systemic resistance-inducing properties of fungal biocontrol agents, such as Trichoderma spp., and that these microbes can be used as vectors to provide plants with useful molecules (e.g., glucose oxidase) that can increase their resistance to pathogens.

Improvement of the Fungal Biocontrol Agent Trichoderma atroviride To Enhance both Antagonism and Induction of Plant Systemic Disease Resistance

PubMed Central

Brunner, Kurt; Zeilinger, Susanne; Ciliento, Rosalia; Woo, Sheridian L.; Lorito, Matteo; Kubicek, Christian P.; Mach, Robert L.

2005-01-01

Biocontrol agents generally do not perform well enough under field conditions to compete with chemical fungicides. We determined whether transgenic strain SJ3-4 of Trichoderma atroviride, which expresses the Aspergillus niger glucose oxidase-encoding gene, goxA, under a homologous chitinase (nag1) promoter had increased capabilities as a fungal biocontrol agent. The transgenic strain differed only slightly from the wild-type in sporulation or the growth rate. goxA expression occurred immediately after contact with the plant pathogen, and the glucose oxidase formed was secreted. SJ3-4 had significantly less N-acetylglucosaminidase and endochitinase activities than its nontransformed parent. Glucose oxidase-containing culture filtrates exhibited threefold-greater inhibition of germination of spores of Botrytis cinerea. The transgenic strain also more quickly overgrew and lysed the plant pathogens Rhizoctonia solani and Pythium ultimum. In planta, SJ3-4 had no detectable improved effect against low inoculum levels of these pathogens. Beans planted in heavily infested soil and treated with conidia of the transgenic Trichoderma strain germinated, but beans treated with wild-type spores did not germinate. SJ3-4 also was more effective in inducing systemic resistance in plants. Beans with SJ3-4 root protection were highly resistant to leaf lesions caused by the foliar pathogen B. cinerea. This work demonstrates that heterologous genes driven by pathogen-inducible promoters can increase the biocontrol and systemic resistance-inducing properties of fungal biocontrol agents, such as Trichoderma spp., and that these microbes can be used as vectors to provide plants with useful molecules (e.g., glucose oxidase) that can increase their resistance to pathogens. PMID:16000810

Diversity, Pathogenicity And Control of Verticillium Species.

USDA-ARS?s Scientific Manuscript database

The genus Verticillium is a cosmopolitan group of ascomycetous fungi, encompassing phytopathogenic species that cause vascular wilts of plants. Two of these species, V. dahliae and V. albo-atrum, cause billions of dollars in annual crop losses worldwide. The soil habitat of these species, the exte...

Deciphering microbial landscapes of fish eggs to mitigate emerging disease

USDA-ARS?s Scientific Manuscript database

Animals and plants are increasingly suffering from diseases caused by fungi and oomycetes. These emerging pathogens are now recognised as a global threat to biodiversity and food security. Amongst oomycetes, Saprolegnia species cause significant declines in fish and amphibian populations. Fish eggs ...

Spatial dynamics and control of a crop pathogen with mixed-mode transmission.

PubMed

McQuaid, Christopher Finn; van den Bosch, Frank; Szyniszewska, Anna; Alicai, Titus; Pariyo, Anthony; Chikoti, Patrick Chiza; Gilligan, Christopher Aidan

2017-07-01

Trade or sharing that moves infectious planting material between farms can, for vertically-transmitted plant diseases, act as a significant force for dispersal of pathogens, particularly where the extent of material movement may be greater than that of infected vectors or inoculum. The network over which trade occurs will then effect dispersal, and is important to consider when attempting to control the disease. We consider the difference that planting material exchange can make to successful control of cassava brown streak disease, an important viral disease affecting one of Africa's staple crops. We use a mathematical model of smallholders' fields to determine the effect of informal trade on both the spread of the pathogen and its control using clean-seed systems, determining aspects that could limit the damage caused by the disease. In particular, we identify the potentially detrimental effects of markets, and the benefits of a community-based approach to disease control.

Fungal phytotoxins with potential herbicidal activity: chemical and biological characterization.

PubMed

Cimmino, Alessio; Masi, Marco; Evidente, Marco; Superchi, Stefano; Evidente, Antonio

2015-12-19

Covering: 2007 to 2015 Fungal phytotoxins are secondary metabolites playing an important role in the induction of disease symptoms interfering with host plant physiological processes. Although fungal pathogens represent a heavy constraint for agrarian production and for forest and environmental heritage, they can also represent an ecofriendly alternative to manage weeds. Indeed, the phytotoxins produced by weed pathogenic fungi are an efficient tool to design natural, safe bioherbicides. Their use could avoid that of synthetic pesticides causing resistance in the host plants and the long term impact of residues in agricultural products with a risk to human and animal health. The isolation and structural and biological characterization of phytotoxins produced by pathogenic fungi for weeds, including parasitic plants, are described. Structure activity relationships and mode of action studies for some phytotoxins are also reported to elucidate the herbicide potential of these promising fungal metabolites.

Streptomyces scabies 87-22 contains a coronafacic acid-like biosynthetic cluster that contributes to plant-microbe interactions.

PubMed

Bignell, Dawn R D; Seipke, Ryan F; Huguet-Tapia, José C; Chambers, Alan H; Parry, Ronald J; Loria, Rosemary

2010-02-01

Plant-pathogenic Streptomyces spp. cause scab disease on economically important root and tuber crops, the most important of which is potato. Key virulence determinants produced by these species include the cellulose synthesis inhibitor, thaxtomin A, and the secreted Nec1 protein that is required for colonization of the plant host. Recently, the genome sequence of Streptomyces scabies 87-22 was completed, and a biosynthetic cluster was identified that is predicted to synthesize a novel compound similar to coronafacic acid (CFA), a component of the virulence-associated coronatine phytotoxin produced by the plant-pathogenic bacterium Pseudomonas syringae. Southern analysis indicated that the cfa-like cluster in S. scabies 87-22 is likely conserved in other strains of S. scabies but is absent from two other pathogenic streptomycetes, S. turgidiscabies and S. acidiscabies. Transcriptional analyses demonstrated that the cluster is expressed during plant-microbe interactions and that expression requires a transcriptional regulator embedded in the cluster as well as the bldA tRNA. A knockout strain of the biosynthetic cluster displayed a reduced virulence phenotype on tobacco seedlings compared with the wild-type strain. Thus, the cfa-like biosynthetic cluster is a newly discovered locus in S. scabies that contributes to host-pathogen interactions.

Plants versus Fungi and Oomycetes: Pathogenesis, Defense and Counter-Defense in the Proteomics Era

PubMed Central

El Hadrami, Abdelbasset; El-Bebany, Ahmed F.; Yao, Zhen; Adam, Lorne R.; El Hadrami, Ismailx; Daayf, Fouad

2012-01-01

Plant-fungi and plant-oomycete interactions have been studied at the proteomic level for many decades. However, it is only in the last few years, with the development of new approaches, combined with bioinformatics data mining tools, gel staining, and analytical instruments, such as 2D-PAGE/nanoflow-LC-MS/MS, that proteomic approaches thrived. They allow screening and analysis, at the sub-cellular level, of peptides and proteins resulting from plants, pathogens, and their interactions. They also highlight post-translational modifications to proteins, e.g., glycosylation, phosphorylation or cleavage. However, many challenges are encountered during in planta studies aimed at stressing details of host defenses and fungal and oomycete pathogenicity determinants during interactions. Dissecting the mechanisms of such host-pathogen systems, including pathogen counter-defenses, will ensure a step ahead towards understanding current outcomes of interactions from a co-evolutionary point of view, and eventually move a step forward in building more durable strategies for management of diseases caused by fungi and oomycetes. Unraveling intricacies of more complex proteomic interactions that involve additional microbes, i.e., PGPRs and symbiotic fungi, which strengthen plant defenses will generate valuable information on how pathosystems actually function in nature, and thereby provide clues to solving disease problems that engender major losses in crops every year. PMID:22837691

A De Novo-Assembly Based Data Analysis Pipeline for Plant Obligate Parasite Metatranscriptomic Studies

PubMed Central

Guo, Li; Allen, Kelly S.; Deiulio, Greg; Zhang, Yong; Madeiras, Angela M.; Wick, Robert L.; Ma, Li-Jun

2016-01-01

Current and emerging plant diseases caused by obligate parasitic microbes such as rusts, downy mildews, and powdery mildews threaten worldwide crop production and food safety. These obligate parasites are typically unculturable in the laboratory, posing technical challenges to characterize them at the genetic and genomic level. Here we have developed a data analysis pipeline integrating several bioinformatic software programs. This pipeline facilitates rapid gene discovery and expression analysis of a plant host and its obligate parasite simultaneously by next generation sequencing of mixed host and pathogen RNA (i.e., metatranscriptomics). We applied this pipeline to metatranscriptomic sequencing data of sweet basil (Ocimum basilicum) and its obligate downy mildew parasite Peronospora belbahrii, both lacking a sequenced genome. Even with a single data point, we were able to identify both candidate host defense genes and pathogen virulence genes that are highly expressed during infection. This demonstrates the power of this pipeline for identifying genes important in host–pathogen interactions without prior genomic information for either the plant host or the obligate biotrophic pathogen. The simplicity of this pipeline makes it accessible to researchers with limited computational skills and applicable to metatranscriptomic data analysis in a wide range of plant-obligate-parasite systems. PMID:27462318

Plants versus fungi and oomycetes: pathogenesis, defense and counter-defense in the proteomics era.

PubMed

El Hadrami, Abdelbasset; El-Bebany, Ahmed F; Yao, Zhen; Adam, Lorne R; El Hadrami, Ismailx; Daayf, Fouad

2012-01-01

Plant-fungi and plant-oomycete interactions have been studied at the proteomic level for many decades. However, it is only in the last few years, with the development of new approaches, combined with bioinformatics data mining tools, gel staining, and analytical instruments, such as 2D-PAGE/nanoflow-LC-MS/MS, that proteomic approaches thrived. They allow screening and analysis, at the sub-cellular level, of peptides and proteins resulting from plants, pathogens, and their interactions. They also highlight post-translational modifications to proteins, e.g., glycosylation, phosphorylation or cleavage. However, many challenges are encountered during in planta studies aimed at stressing details of host defenses and fungal and oomycete pathogenicity determinants during interactions. Dissecting the mechanisms of such host-pathogen systems, including pathogen counter-defenses, will ensure a step ahead towards understanding current outcomes of interactions from a co-evolutionary point of view, and eventually move a step forward in building more durable strategies for management of diseases caused by fungi and oomycetes. Unraveling intricacies of more complex proteomic interactions that involve additional microbes, i.e., PGPRs and symbiotic fungi, which strengthen plant defenses will generate valuable information on how pathosystems actually function in nature, and thereby provide clues to solving disease problems that engender major losses in crops every year.

Shared signals and the potential for phylogenetic espionage between plants and animals.

PubMed

Schultz, Jack C

2002-07-01

Until recently, the study and understanding of plant and animal signalling and response mechanisms have developed independently. Recent biochemical and molecular work is producing a growing list of elements involved in responses to biotic and abiotic stimuli that are very similar across kingdoms. Some of the more interesting examples of these include prostaglandin/octadecanoid-mediated responses to wounding, steroid-based signalling systems, and pathogen-recognition mechanisms. Some of these similarities probably represent evolutionary convergence; others may be ancestral to plants and animals. Ecological and evolutionary implications of such overlaps include the existence of pathogens that can cause disease in plants and animals, the ability of herbivores to manipulate plant responses, usurpation of microbial mechanisms and genes by herbivorous animals and plants, evolution of plant defenses exploiting shared signals in animals, and the medicinal use of plants by humans. Comparative study of the signalling and response mechanisms used by plants, animals, and microbes provides novel and useful insights to the ecology and evolution of interactions across kingdoms.

The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes.

PubMed

Goss, Erica M; Tabima, Javier F; Cooke, David E L; Restrepo, Silvia; Fry, William E; Forbes, Gregory A; Fieland, Valerie J; Cardenas, Martha; Grünwald, Niklaus J

2014-06-17

Phytophthora infestans is a destructive plant pathogen best known for causing the disease that triggered the Irish potato famine and remains the most costly potato pathogen to manage worldwide. Identification of P. infestan's elusive center of origin is critical to understanding the mechanisms of repeated global emergence of this pathogen. There are two competing theories, placing the origin in either South America or in central Mexico, both of which are centers of diversity of Solanum host plants. To test these competing hypotheses, we conducted detailed phylogeographic and approximate Bayesian computation analyses, which are suitable approaches to unraveling complex demographic histories. Our analyses used microsatellite markers and sequences of four nuclear genes sampled from populations in the Andes, Mexico, and elsewhere. To infer the ancestral state, we included the closest known relatives Phytophthora phaseoli, Phytophthora mirabilis, and Phytophthora ipomoeae, as well as the interspecific hybrid Phytophthora andina. We did not find support for an Andean origin of P. infestans; rather, the sequence data suggest a Mexican origin. Our findings support the hypothesis that populations found in the Andes are descendants of the Mexican populations and reconcile previous findings of ancestral variation in the Andes. Although centers of origin are well documented as centers of evolution and diversity for numerous crop plants, the number of plant pathogens with a known geographic origin are limited. This work has important implications for our understanding of the coevolution of hosts and pathogens, as well as the harnessing of plant disease resistance to manage late blight.

Development of Inhibitors of Salicylic Acid Signaling.

PubMed

Jiang, Kai; Kurimoto, Tetsuya; Seo, Eun-kyung; Miyazaki, Sho; Nakajima, Masatoshi; Nakamura, Hidemitsu; Asami, Tadao

2015-08-19

Salicylic acid (SA) plays important roles in the induction of systemic acquired resistance (SAR) in plants. Determining the mechanism of SAR will extend our understanding of plant defenses against pathogens. We recently reported that PAMD is an inhibitor of SA signaling, which suppresses the expression of the pathogenesis-related PR genes and is expected to facilitate the understanding of SA signaling. However, PAMD strongly inhibits plant growth. To minimize the side effects of PAMD, we synthesized a number of PAMD derivatives, and identified compound 4 that strongly suppresses the expression of the PR genes with fewer adverse effects on plant growth than PAMD. We further showed that the adverse effects on plant growth were partially caused the stabilization of DELLA, which is also related to the pathogen responses. These results indicate that compound 4 would facilitate our understanding of SA signaling and its cross talk with other plant hormones.

Trafficking arms: oomycete effectors enter host plant cells.

PubMed

Birch, Paul R J; Rehmany, Anne P; Pritchard, Leighton; Kamoun, Sophien; Beynon, Jim L

2006-01-01

Oomycetes cause devastating plant diseases of global importance, yet little is known about the molecular basis of their pathogenicity. Recently, the first oomycete effector genes with cultivar-specific avirulence (AVR) functions were identified. Evidence of diversifying selection in these genes and their cognate plant host resistance genes suggests a molecular "arms race" as plants and oomycetes attempt to achieve and evade detection, respectively. AVR proteins from Hyaloperonospora parasitica and Phytophthora infestans are detected in the plant host cytoplasm, consistent with the hypothesis that oomycetes, as is the case with bacteria and fungi, actively deliver effectors inside host cells. The RXLR amino acid motif, which is present in these AVR proteins and other secreted oomycete proteins, is similar to a host-cell-targeting signal in virulence proteins of malaria parasites (Plasmodium species), suggesting a conserved role in pathogenicity.

The NADPH oxidase Cpnox1 is required for full pathogenicity of the ergot fungus Claviceps purpurea.

PubMed

Giesbert, Sabine; Schürg, Timo; Scheele, Sandra; Tudzynski, Paul

2008-05-01

The role of reactive oxygen species (ROS) in interactions between phytopathogenic fungi and their hosts is well established. An oxidative burst mainly caused by superoxide formation by membrane-associated NADPH oxidases is an essential element of plant defence reactions. Apart from primary effects, ROS play a major role as a second messenger in host response. Recently, NADPH oxidase (nox)-encoding genes have been identified in filamentous fungi. Functional analyses have shown that these fungal enzymes are involved in sexual differentiation, and there is growing evidence that they also affect developmental programmes involved in fungus-plant interactions. Here we show that in the biotrophic plant pathogen Claviceps purpurea deletion of the cpnox1 gene, probably encoding an NADPH oxidase, has impact on germination of conidia and pathogenicity: Deltacpnox1 mutants can penetrate the host epidermis, but they are impaired in colonization of the plant ovarian tissue. In the few cases where macroscopic signs of infection (honeydew) appear, they are extremely delayed and fully developed sclerotia have never been observed. C. purpurea Nox1 is important for the interaction with its host, probably by directly affecting pathogenic differentiation of the fungus.

Antagonism between phytohormone signalling underlies the variation in disease susceptibility of tomato plants under elevated CO2.

PubMed

Zhang, Shuai; Li, Xin; Sun, Zenghui; Shao, Shujun; Hu, Lingfei; Ye, Meng; Zhou, Yanhong; Xia, Xiaojian; Yu, Jingquan; Shi, Kai

2015-04-01

Increasing CO2 concentrations ([CO2]) have the potential to disrupt plant-pathogen interactions in natural and agricultural ecosystems, but the research in this area has often produced conflicting results. Variations in phytohormone salicylic acid (SA) and jasmonic acid (JA) signalling could be associated with variations in the responses of pathogens to plants grown under elevated [CO2]. In this study, interactions between tomato plants and three pathogens with different infection strategies were compared. Elevated [CO2] generally favoured SA biosynthesis and signalling but repressed the JA pathway. The exposure of plants to elevated [CO2] revealed a lower incidence and severity of disease caused by tobacco mosaic virus (TMV) and by Pseudomonas syringae, whereas plant susceptibility to necrotrophic Botrytis cinerea increased. The elevated [CO2]-induced and basal resistance to TMV and P. syringae were completely abolished in plants in which the SA signalling pathway nonexpressor of pathogenesis-related genes 1 (NPR1) had been silenced or in transgenic plants defective in SA biosynthesis. In contrast, under both ambient and elevated [CO2], the susceptibility to B. cinerea highly increased in plants in which the JA signalling pathway proteinase inhibitors (PI) gene had been silenced or in a mutant affected in JA biosynthesis. However, plants affected in SA signalling remained less susceptible to this disease. These findings highlight the modulated antagonistic relationship between SA and JA that contributes to the variation in disease susceptibility under elevated [CO2]. This information will be critical for investigating how elevated CO2 may affect plant defence and the dynamics between plants and pathogens in both agricultural and natural ecosystems. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Antioxidant genes of plants and fungal pathogens are distinctly regulated during disease development in different Rhizoctonia solani pathosystems

PubMed Central

Samsatly, Jamil; Copley, Tanya R.

2018-01-01

Biotic stress, as a result of plant-pathogen interactions, induces the accumulation of reactive oxygen species in the cells, causing severe oxidative damage to plants and pathogens. To overcome this damage, both the host and pathogen have developed antioxidant systems to quench excess ROS and keep ROS production and scavenging systems under control. Data on ROS-scavenging systems in the necrotrophic plant pathogen Rhizoctonia solani are just emerging. We formerly identified vitamin B6 biosynthetic machinery of R. solani AG3 as a powerful antioxidant exhibiting a high ability to quench ROS, similar to CATALASE (CAT) and GLUTATHIONE S-TRANSFERASE (GST). Here, we provide evidence on the involvement of R. solani vitamin B6 biosynthetic pathway genes; RsolPDX1 (KF620111.1), RsolPDX2 (KF620112.1), and RsolPLR (KJ395592.1) in vitamin B6 de novo biosynthesis by yeast complementation assays. Since gene expression studies focusing on oxidative stress responses of both the plant and the pathogen following R. solani infection are very limited, this study is the first coexpression analysis of genes encoding vitamin B6, CAT and GST in plant and fungal tissues of three pathosystems during interaction of different AG groups of R. solani with their respective hosts. The findings indicate that distinct expression patterns of fungal and host antioxidant genes were correlated in necrotic tissues and their surrounding areas in each of the three R. solani pathosystems: potato sprout-R. solani AG3; soybean hypocotyl-R. solani AG4 and soybean leaves-R. solani AG1-IA interactions. Levels of ROS increased in all types of potato and soybean tissues, and in fungal hyphae following infection of R. solani AGs as determined by non-fluorescence and fluorescence methods using H2DCF-DA and DAB, respectively. Overall, we demonstrate that the co-expression and accumulation of certain plant and pathogen ROS-antioxidant related genes in each pathosystem are highlighted and might be critical during disease development from the plant’s point of view, and in pathogenicity and developing of infection structures from the fungal point of view. PMID:29466404

Apoplastic effectors secreted by two unrelated eukaryotic plant pathogens target the tomato defense protease Rcr3.

PubMed

Song, Jing; Win, Joe; Tian, Miaoying; Schornack, Sebastian; Kaschani, Farnusch; Ilyas, Muhammad; van der Hoorn, Renier A L; Kamoun, Sophien

2009-02-03

Current models of plant-pathogen interactions stipulate that pathogens secrete effector proteins that disable plant defense components known as virulence targets. Occasionally, the perturbations caused by these effectors trigger innate immunity via plant disease resistance proteins as described by the "guard hypothesis." This model is nicely illustrated by the interaction between the fungal plant pathogen Cladosporium fulvum and tomato. C. fulvum secretes a protease inhibitor Avr2 that targets the tomato cysteine protease Rcr3(pim). In plants that carry the resistance protein Cf2, Rcr3(pim) is required for resistance to C. fulvum strains expressing Avr2, thus fulfilling one of the predictions of the guard hypothesis. Another prediction of the guard hypothesis has not yet been tested. Considering that virulence targets are important components of defense, different effectors from unrelated pathogens are expected to evolve to disable the same host target. In this study we confirm this prediction using a different pathogen of tomato, the oomycete Phytophthora infestans that is distantly related to fungi such as C. fulvum. This pathogen secretes an array of protease inhibitors including EPIC1 and EPIC2B that inhibit tomato cysteine proteases. Here we show that, similar to Avr2, EPIC1 and EPIC2B bind and inhibit Rcr3(pim). However, unlike Avr2, EPIC1 and EPIC2B do not trigger hypersensitive cell death or defenses on Cf-2/Rcr3(pim) tomato. We also found that the rcr3-3 mutant of tomato that carries a premature stop codon in the Rcr3 gene exhibits enhanced susceptibility to P. infestans, suggesting a role for Rcr3(pim) in defense. In conclusion, our findings fulfill a key prediction of the guard hypothesis and suggest that the effectors Avr2, EPIC1, and EPIC2B secreted by two unrelated pathogens of tomato target the same defense protease Rcr3(pim). In contrast to C. fulvum, P. infestans appears to have evolved stealthy effectors that carry inhibitory activity without triggering plant innate immunity.

Metabolic Environments and Genomic Features Associated with Pathogenic and Mutualistic Interactions between Bacteria and Plants is accepted for publication in MPMI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karpinets, Tatiana V; Park, Byung H; Syed, Mustafa H

Most bacterial symbionts of plants are phenotypically characterized by their parasitic or matualistic relationship with the host; however, the genomic characteristics that likely discriminate mutualistic symbionts from pathogens of plants are poorly understood. This study comparatively analyzed the genomes of 54 plant-symbiontic bacteria, 27 mutualists and 27 pathogens, to discover genomic determinants of their parasitic and mutualistic nature in terms of protein family domains, KEGG orthologous groups, metabolic pathways and families of carbohydrate-active enzymes (CAZymes). We further used all bacteria with sequenced genomesl, published microarrays and transcriptomics experimental datasets, and literature to validate and to explore results of the comparison.more » The analysis revealed that genomes of mutualists are larger in size and higher in GC content and encode greater molecular, functional and metabolic diversity than the investigated genomes of pathogens. This enriched molecular and functional enzyme diversity included constructive biosynthetic signatures of CAZymes and metabolic pathways in genomes of mutualists compared with catabolic signatures dominant in the genomes of pathogens. Another discriminative characteristic of mutualists is the co-occurence of gene clusters required for the expression and function of nitrogenase and RuBisCO. Analysis of previously published experimental data indicate that nitrogen-fixing mutualists may employ Rubisco to fix CO2 not in the canonical Calvin-Benson-Basham cycle but in a novel metabolic pathway, here called Rubisco-based glycolysis , to increase efficiency of sugar utilization during the symbiosis with plants. An important discriminative characteristic of plant pathogenic bacteria is two groups of genes likely encoding effector proteins involved in host invasion and a genomic locus encoding a putative secretion system that includes a DUF1525 domain protein conserved in pathogens of plants and of other organisms. The protein belongs to the same clan of thioredoxins as the circadian clock protein kaiB found in many mutualistic symbionts and highly abundant in blood cells colonized by a human pathogen, Salmonella enterica serotype Typhi, the cause of typhoid fever.« less

Using NextRAD sequencing to infer movement of herbivores among host plants.

PubMed

Fu, Zhen; Epstein, Brendan; Kelley, Joanna L; Zheng, Qi; Bergland, Alan O; Castillo Carrillo, Carmen I; Jensen, Andrew S; Dahan, Jennifer; Karasev, Alexander V; Snyder, William E

2017-01-01

Herbivores often move among spatially interspersed host plants, tracking high-quality resources through space and time. This dispersal is of particular interest for vectors of plant pathogens. Existing molecular tools to track such movement have yielded important insights, but often provide insufficient genetic resolution to infer spread at finer spatiotemporal scales. Here, we explore the use of Nextera-tagmented reductively-amplified DNA (NextRAD) sequencing to infer movement of a highly-mobile winged insect, the potato psyllid (Bactericera cockerelli), among host plants. The psyllid vectors the pathogen that causes zebra chip disease in potato (Solanum tuberosum), but understanding and managing the spread of this pathogen is limited by uncertainty about the insect's host plant(s) outside of the growing season. We identified 1,978 polymorphic loci among psyllids separated spatiotemporally on potato or in patches of bittersweet nightshade (S. dulcumara), a weedy plant proposed to be the source of potato-colonizing psyllids. A subset of the psyllids on potato exhibited genetic similarity to insects on nightshade, consistent with regular movement between these two host plants. However, a second subset of potato-collected psyllids was genetically distinct from those collected on bittersweet nightshade; this suggests that a currently unrecognized source, i.e., other nightshade patches or a third host-plant species, could be contributing to psyllid populations in potato. Oftentimes, dispersal of vectors of pathogens must be tracked at a fine scale in order to understand, predict, and manage disease spread. We demonstrate that emerging sequencing technologies that detect genome-wide SNPs of a vector can be used to infer such localized movement.

Phytophthora cinnamomi.

PubMed

Hardham, Adrienne R; Blackman, Leila M

2018-02-01

Phytophthora cinnamomi is one of the most devastating plant pathogens in the world. It infects close to 5000 species of plants, including many of importance in agriculture, forestry and horticulture. The inadvertent introduction of P. cinnamomi into natural ecosystems, including a number of recognized Global Biodiversity Hotspots, has had disastrous consequences for the environment and the biodiversity of flora and fauna. The genus Phytophthora belongs to the Class Oomycetes, a group of fungus-like organisms that initiate plant disease through the production of motile zoospores. Disease control is difficult in agricultural and forestry situations and even more challenging in natural ecosystems as a result of the scale of the problem and the limited range of effective chemical inhibitors. The development of sustainable control measures for the future management of P. cinnamomi requires a comprehensive understanding of the cellular and molecular basis of pathogen development and pathogenicity. The application of next-generation sequencing technologies to generate genomic and transcriptomic data promises to underpin a new era in P. cinnamomi research and discovery. The aim of this review is to integrate bioinformatic analyses of P. cinnamomi sequence data with current knowledge of the cellular and molecular basis of P. cinnamomi growth, development and plant infection. The goal is to provide a framework for future research by highlighting potential pathogenicity genes, shedding light on their possible functions and identifying suitable targets for future control measures. Phytophthora cinnamomi Rands; Kingdom Chromista; Phylum Oomycota or Pseudofungi; Class Oomycetes; Order Peronosporales; Family Peronosporaceae; genus Phytophthora. Infects about 5000 species of plants, including 4000 Australian native species. Host plants important for agriculture and forestry include avocado, chestnut, macadamia, oak, peach and pineapple. A root pathogen which causes rotting of fine and fibrous roots, but which can also cause stem cankers. Root damage may inhibit water movement from roots to shoots, leading to dieback of young shoots. USEFUL WEBSITES: http://fungidb.org/fungidb/; http://genome.jgi.doe.gov/Phyci1/Phyci1.home.html; http://www.ncbi.nlm.nih.gov/assembly/GCA_001314365.1; http://www.ncbi.nlm.nih.gov/assembly/GCA_001314505.1. © 2017 BSPP AND JOHN WILEY & SONS LTD.

Defense responses regulated by jasmonate and delayed senescence caused by ethylene receptor mutation contribute to tolerance of petunia to Botrytis cinerea

USDA-ARS?s Scientific Manuscript database

The death of cells can be a programmed event that occurs when plants are attacked by pathogens. Botrytis cinerea (B. cinerea), a model necrotrophic pathogen, triggers the host cell death response because it produces toxins. A hypersensitive reaction (HR) occurs at the site of contact. In Arabidopsis...

Role of major surface structures of Escherichia coli O157:H7 in initial attachment to biotic and abiotic surfaces

USDA-ARS?s Scientific Manuscript database

Infection by human pathogens through fresh, minimally processed produce and solid plant-derived foods is a major concern of U.S. and global food industry and public health services. The enterohemorrhagic Escherichia coli O157:H7 is a frequent and potent food borne pathogen that causes severe disease...

The genome sequence of the plant pathogen Xylella fastidiosa. The Xylella fastidiosa Consortium of the Organization for Nucleotide Sequencing and Analysis.

PubMed

Simpson, A J; Reinach, F C; Arruda, P; Abreu, F A; Acencio, M; Alvarenga, R; Alves, L M; Araya, J E; Baia, G S; Baptista, C S; Barros, M H; Bonaccorsi, E D; Bordin, S; Bové, J M; Briones, M R; Bueno, M R; Camargo, A A; Camargo, L E; Carraro, D M; Carrer, H; Colauto, N B; Colombo, C; Costa, F F; Costa, M C; Costa-Neto, C M; Coutinho, L L; Cristofani, M; Dias-Neto, E; Docena, C; El-Dorry, H; Facincani, A P; Ferreira, A J; Ferreira, V C; Ferro, J A; Fraga, J S; França, S C; Franco, M C; Frohme, M; Furlan, L R; Garnier, M; Goldman, G H; Goldman, M H; Gomes, S L; Gruber, A; Ho, P L; Hoheisel, J D; Junqueira, M L; Kemper, E L; Kitajima, J P; Krieger, J E; Kuramae, E E; Laigret, F; Lambais, M R; Leite, L C; Lemos, E G; Lemos, M V; Lopes, S A; Lopes, C R; Machado, J A; Machado, M A; Madeira, A M; Madeira, H M; Marino, C L; Marques, M V; Martins, E A; Martins, E M; Matsukuma, A Y; Menck, C F; Miracca, E C; Miyaki, C Y; Monteriro-Vitorello, C B; Moon, D H; Nagai, M A; Nascimento, A L; Netto, L E; Nhani, A; Nobrega, F G; Nunes, L R; Oliveira, M A; de Oliveira, M C; de Oliveira, R C; Palmieri, D A; Paris, A; Peixoto, B R; Pereira, G A; Pereira, H A; Pesquero, J B; Quaggio, R B; Roberto, P G; Rodrigues, V; de M Rosa, A J; de Rosa, V E; de Sá, R G; Santelli, R V; Sawasaki, H E; da Silva, A C; da Silva, A M; da Silva, F R; da Silva, W A; da Silveira, J F; Silvestri, M L; Siqueira, W J; de Souza, A A; de Souza, A P; Terenzi, M F; Truffi, D; Tsai, S M; Tsuhako, M H; Vallada, H; Van Sluys, M A; Verjovski-Almeida, S; Vettore, A L; Zago, M A; Zatz, M; Meidanis, J; Setubal, J C

2000-07-13

Xylella fastidiosa is a fastidious, xylem-limited bacterium that causes a range of economically important plant diseases. Here we report the complete genome sequence of X. fastidiosa clone 9a5c, which causes citrus variegated chlorosis--a serious disease of orange trees. The genome comprises a 52.7% GC-rich 2,679,305-base-pair (bp) circular chromosome and two plasmids of 51,158 bp and 1,285 bp. We can assign putative functions to 47% of the 2,904 predicted coding regions. Efficient metabolic functions are predicted, with sugars as the principal energy and carbon source, supporting existence in the nutrient-poor xylem sap. The mechanisms associated with pathogenicity and virulence involve toxins, antibiotics and ion sequestration systems, as well as bacterium-bacterium and bacterium-host interactions mediated by a range of proteins. Orthologues of some of these proteins have only been identified in animal and human pathogens; their presence in X. fastidiosa indicates that the molecular basis for bacterial pathogenicity is both conserved and independent of host. At least 83 genes are bacteriophage-derived and include virulence-associated genes from other bacteria, providing direct evidence of phage-mediated horizontal gene transfer.

Plant defense response against Fusarium oxysporum and strategies to develop tolerant genotypes in banana.

PubMed

Swarupa, V; Ravishankar, K V; Rekha, A

2014-04-01

Soil-borne fungal pathogen, Fusarium oxysporum causes major economic losses by inducing necrosis and wilting symptoms in many crop plants. Management of fusarium wilt is achieved mainly by the use of chemical fungicides which affect the soil health and their efficiency is often limited by pathogenic variability. Hence understanding the nature of interaction between pathogen and host may help to select and improve better cultivars. Current research evidences highlight the role of oxidative burst and antioxidant enzymes indicating that ROS act as an important signaling molecule in banana defense response against Fusarium oxysporum f.sp. cubense. The role of jasmonic acid signaling in plant defense against necrotrophic pathogens is well recognized. But recent studies show that the role of salicylic acid is complex and ambiguous against necrotrophic pathogens like Fusarium oxysporum, leading to many intriguing questions about its relationship between other signaling compounds. In case of banana, a major challenge is to identify specific receptors for effector proteins like SIX proteins and also the components of various signal transduction pathways. Significant progress has been made to uncover the role of defense genes but is limited to only model plants such as Arabidopsis and tomato. Keeping this in view, we review the host response, pathogen diversity, current understanding of biochemical and molecular changes that occur during host and pathogen interaction. Developing resistant cultivars through mutation, breeding, transgenic and cisgenic approaches have been discussed. This would help us to understand host defenses against Fusarium oxysporum and to formulate strategies to develop tolerant cultivars.

Antagonism between phytohormone signalling underlies the variation in disease susceptibility of tomato plants under elevated CO2

PubMed Central

Zhang, Shuai; Li, Xin; Sun, Zenghui; Shao, Shujun; Hu, Lingfei; Ye, Meng; Zhou, Yanhong; Xia, Xiaojian; Yu, Jingquan; Shi, Kai

2015-01-01

Increasing CO2 concentrations ([CO2]) have the potential to disrupt plant–pathogen interactions in natural and agricultural ecosystems, but the research in this area has often produced conflicting results. Variations in phytohormone salicylic acid (SA) and jasmonic acid (JA) signalling could be associated with variations in the responses of pathogens to plants grown under elevated [CO2]. In this study, interactions between tomato plants and three pathogens with different infection strategies were compared. Elevated [CO2] generally favoured SA biosynthesis and signalling but repressed the JA pathway. The exposure of plants to elevated [CO2] revealed a lower incidence and severity of disease caused by tobacco mosaic virus (TMV) and by Pseudomonas syringae, whereas plant susceptibility to necrotrophic Botrytis cinerea increased. The elevated [CO2]-induced and basal resistance to TMV and P. syringae were completely abolished in plants in which the SA signalling pathway nonexpressor of pathogenesis-related genes 1 (NPR1) had been silenced or in transgenic plants defective in SA biosynthesis. In contrast, under both ambient and elevated [CO2], the susceptibility to B. cinerea highly increased in plants in which the JA signalling pathway proteinase inhibitors (PI) gene had been silenced or in a mutant affected in JA biosynthesis. However, plants affected in SA signalling remained less susceptible to this disease. These findings highlight the modulated antagonistic relationship between SA and JA that contributes to the variation in disease susceptibility under elevated [CO2]. This information will be critical for investigating how elevated CO2 may affect plant defence and the dynamics between plants and pathogens in both agricultural and natural ecosystems. PMID:25657213

Arabidopsis serotonin N-acetyltransferase knockout mutant plants exhibit decreased melatonin and salicylic acid levels resulting in susceptibility to an avirulent pathogen.

PubMed

Lee, Hyoung Yool; Byeon, Yeong; Tan, Dun-Xian; Reiter, Russel J; Back, Kyoungwhan

2015-04-01

Serotonin N-acetyltransferase (SNAT) is the penultimate enzyme in the melatonin biosynthesis pathway in plants. We examined the effects of SNAT gene inactivation in two Arabidopsis T-DNA insertion mutant lines. After inoculation with the avirulent pathogen Pseudomonas syringe pv. tomato DC3000 harboring the elicitor avrRpt2 (Pst-avrRpt2), melatonin levels in the snat knockout mutant lines were 50% less than in wild-type Arabidopsis Col-0 plants. The snat knockout mutant lines exhibited susceptibility to pathogen infection that coincided with decreased induction of defense genes including PR1, ICS1, and PDF1.2. Because melatonin acts upstream of salicylic acid (SA) synthesis, the reduced melatonin levels in the snat mutant lines led to decreased SA levels compared to wild-type, suggesting that the increased pathogen susceptibility of the snat mutant lines could be attributed to decreased SA levels and subsequent attenuation of defense gene induction. Exogenous melatonin treatment failed to induce defense gene expression in nahG Arabidopsis plants, but restored the induction of defense gene expression in the snat mutant lines. In addition, melatonin caused translocation of NPR1 (nonexpressor of PR1) protein from the cytoplasm into the nucleus indicating that melatonin-elicited pathogen resistance in response to avirulent pathogen attack is SA-dependent in Arabidopsis. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

The type III secretion system is necessary for the development of a pathogenic and endophytic interaction between Herbaspirillum rubrisubalbicans and Poaceae

PubMed Central

2012-01-01

Background Herbaspirillum rubrisubalbicans was first identified as a bacterial plant pathogen, causing the mottled stripe disease in sugarcane. H. rubrisubalbicans can also associate with various plants of economic interest in a non pathogenic manner. Results A 21 kb DNA region of the H. rubrisubalbicans genome contains a cluster of 26 hrp/hrc genes encoding for the type three secretion system (T3SS) proteins. To investigate the contribution of T3SS to the plant-bacterial interaction process we generated mutant strains of H. rubrisubalbicans M1 carrying a Tn5 insertion in both the hrcN and hrpE genes. H. rubrisulbalbicans hrpE and hrcN mutant strains of the T3SS system failed to cause the mottled stripe disease in the sugarcane susceptible variety B-4362. These mutant strains also did not produce lesions on Vigna unguiculata leaves. Oryza sativa and Zea mays colonization experiments showed that mutations in hrpE and hrcN genes reduced the capacity of H. rubrisulbalbicans to colonize these plants, suggesting that hrpE and hrcN genes are involved in the endophytic colonization. Conclusions Our results indicate that the T3SS of H. rubrisubalbicans is necessary for the development of the mottled stripe disease and endophytic colonization of rice. PMID:22672506

Pathogen and biological contamination management in plant tissue culture: phytopathogens, vitro pathogens, and vitro pests.

PubMed

Cassells, Alan C

2012-01-01

The ability to establish and grow plant cell, organ, and tissue cultures has been widely exploited for basic and applied research, and for the commercial production of plants (micro-propagation). Regardless of whether the application is for research or commerce, it is essential that the cultures be established in vitro free of biological contamination and be maintained as aseptic cultures during manipulation, growth, and storage. The risks from microbial contamination are spurious experimental results due to the effects of latent contaminants or losses of valuable experimental or commercial cultures. Much of the emphasis in culture contamination management historically focussed on the elimination of phytopathogens and the maintenance of cultures free from laboratory contamination by environmental bacteria, fungi (collectively referred to as "vitro pathogens", i.e. pathogens or environmental micro-organisms which cause culture losses), and micro-arthropods ("vitro pests"). Microbial contamination of plant tissue cultures is due to the high nutrient availability in the almost universally used Murashige and Skoog (Physiol Plant 15:473-497, 1962) basal medium or variants of it. In recent years, it has been shown that many plants, especially perennials, are at least locally endophytically colonized intercellularly by bacteria. The latter, and intracellular pathogenic bacteria and viruses/viroids, may pass latently into culture and be spread horizontally and vertically in cultures. Growth of some potentially cultivable endophytes may be suppressed by the high salt and sugar content of the Murashige and Skoog basal medium and suboptimal temperatures for their growth in plant tissue growth rooms. The management of contamination in tissue culture involves three stages: disease screening (syn. disease indexing) of the stock plants with disease and endophyte elimination where detected; establishment and pathogen and contaminant screening of established initial cultures; observation, random sampling, and culture screening for micro-organism in multiplication and stored cultures. The increasing accessibility of both broad-spectrum and specific molecular diagnostics has resulted in advances in multiple pathogen and latent contaminant detection. The hazard analysis critical control point management strategy for tissue culture laboratories is underpinned by staff training in aseptic technique and good laboratory practice.

Digital PCR technology for detection of palm infecting phytoplasmas belonging to group 16SrIV that occur in Florida

USDA-ARS?s Scientific Manuscript database

Phytoplasmas are an economically important group of plant pathogens that negatively impact a wide variety of plants in agricultural and natural ecosystems. In Florida, palms are essential elements in the nursery and landscaping industries that suffer from diseases caused by phytoplasmas that are rel...

Invasive pathogen threatens bird-pine mutualism: Implications for sustaining a high-elevation ecosystem

Treesearch

Shawn T. McKinney; Carl E. Fiedler; Diana F. Tomback

2009-01-01

Human-caused disruptions to seed-dispersal mutualisms increase the extinction risk for both plant and animal species. Large-seeded plants can be particularly vulnerable due to highly specialized dispersal systems and no compensatory regeneration mechanisms. Whitebark pine (Pinus albicaulis), a keystone subalpine species, obligately depends upon the Clark's...

Predicting pre-planting risk of Stagonospora nodorum blotch in winter wheat using machine learning models

USDA-ARS?s Scientific Manuscript database

Pre-planting factors have been associated with the late-season severity of Stagonospora nodorum blotch (SNB), caused by the fungal pathogen Parastagonospora nodorum, in winter wheat (Triticum aestivum). The relative importance of these factors in the risk of SNB has not been determined and this know...

Escaping Underground Nets: Extracellular DNases Degrade Plant Extracellular Traps and Contribute to Virulence of the Plant Pathogenic Bacterium Ralstonia solanacearum

PubMed Central

Tran, Tuan Minh; MacIntyre, April; Hawes, Martha; Allen, Caitilyn

2016-01-01

Plant root border cells have been recently recognized as an important physical defense against soil-borne pathogens. Root border cells produce an extracellular matrix of protein, polysaccharide and DNA that functions like animal neutrophil extracellular traps to immobilize pathogens. Exposing pea root border cells to the root-infecting bacterial wilt pathogen Ralstonia solanacearum triggered release of DNA-containing extracellular traps in a flagellin-dependent manner. These traps rapidly immobilized the pathogen and killed some cells, but most of the entangled bacteria eventually escaped. The R. solanacearum genome encodes two putative extracellular DNases (exDNases) that are expressed during pathogenesis, suggesting that these exDNases contribute to bacterial virulence by enabling the bacterium to degrade and escape root border cell traps. We tested this hypothesis with R. solanacearum deletion mutants lacking one or both of these nucleases, named NucA and NucB. Functional studies with purified proteins revealed that NucA and NucB are non-specific endonucleases and that NucA is membrane-associated and cation-dependent. Single ΔnucA and ΔnucB mutants and the ΔnucA/B double mutant all had reduced virulence on wilt-susceptible tomato plants in a naturalistic soil-soak inoculation assay. The ΔnucA/B mutant was out-competed by the wild-type strain in planta and was less able to stunt root growth or colonize plant stems. Further, the double nuclease mutant could not escape from root border cells in vitro and was defective in attachment to pea roots. Taken together, these results demonstrate that extracellular DNases are novel virulence factors that help R. solanacearum successfully overcome plant defenses to infect plant roots and cause bacterial wilt disease. PMID:27336156

Oak Tree Canker Disease Supports Arthropod Diversity in a Natural Ecosystem

PubMed Central

Lee, Yong-Bok; An, Su Jung; Park, Chung Gyoo; Kim, Jinwoo; Han, Sangjo; Kwak, Youn-Sig

2014-01-01

Microorganisms have many roles in nature. They may act as decomposers that obtain nutrients from dead materials, while some are pathogens that cause diseases in animals, insects, and plants. Some are symbionts that enhance plant growth, such as arbuscular mycorrhizae and nitrogen fixation bacteria. However, roles of plant pathogens and diseases in natural ecosystems are still poorly understood. Thus, the current study addressed this deficiency by investigating possible roles of plant diseases in natural ecosystems, particularly, their positive effects on arthropod diversity. In this study, the model system was the oak tree (Quercus spp.) and the canker disease caused by Annulohypoxylon truncatum, and its effects on arthropod diversity. The oak tree site contained 44 oak trees; 31 had canker disease symptoms while 13 were disease-free. A total of 370 individual arthropods were detected at the site during the survey period. The arthropods belonged to 25 species, 17 families, and seven orders. Interestingly, the cankered trees had significantly higher biodiversity and richness compared with the canker-free trees. This study clearly demonstrated that arthropod diversity was supported by the oak tree canker disease. PMID:25288984

A Multiple Decrement Life Table Reveals That Host Plant Resistance and Parasitism Are Major Causes of Mortality for the Wheat Stem Sawfly.

PubMed

Buteler, Micaela; Peterson, Robert K D; Hofland, Megan L; Weaver, David K

2015-12-01

This study investigated the dynamics of parasitism, host plant resistance, pathogens, and predation on the demography of wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), developing in susceptible (hollow stem) and resistant (solid stem) wheat hosts. This study is also the first to investigate the prevalence and impact of cannibalism on wheat stem sawfly mortality. Wheat stem sawflies were sampled in two commercial wheat fields over 4 yr from the egg stage through adult emergence, and multiple decrement life tables were constructed and analyzed. Cannibalism, host plant resistance, or unknown factors were the most prevalent factors causing egg mortality. Summer mortality of prediapause larvae ranged from 28 to 84%, mainly due to parasitism by Bracon cephi (Gahan) and Bracon lissogaster Muesebeck, cannibalism, and host plant resistance. Winter mortality ranged from 6 to 54% of the overwintering larvae, mainly due to unknown factors or pathogens. Cannibalism is a major cause of irreplaceable mortality because it is absolute, with only a single survivor in every multiple infested stem. Subsequent to obligate cannibalism, mortality of feeding larvae due to host plant resistance was lower in hollow stem wheat than in solid stem wheat. Mortality from host plant resistance was largely irreplaceable. Irreplaceable mortality due to parasitoids was greater in hollow stem wheat than in solid stem wheat. Host plant resistance due to stem solidness and parasitism in hollow stems cause substantial mortality in populations of actively feeding larvae responsible for all crop losses. Therefore, enhancing these mortality factors is vital to effective integrated pest management of wheat stem sawfly. © The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

A small cysteine-rich protein from the Asian soybean rust fungus, Phakopsora pachyrhizi, suppresses plant immunity

USDA-ARS?s Scientific Manuscript database

The Asian soybean rust fungus, Phakopsora pachyrhizi, is an obligate pathogen capable of causing explosive disease epidemics that drastically reduce the yield of soybean (Glycine max). Currently, the molecular mechanisms by which P. pachyrhizi and other rust fungi cause disease are poorly understood...

Loop-mediated isothermal amplification (LAMP) based detection of Colletotrichum falcatum causing red rot in sugarcane

USDA-ARS?s Scientific Manuscript database

Red rot, caused by Colletotrichum falcatum, is a destructive disease prevalent in most sugarcane-producing countries. Disease-free sugarcane planting materials are essential as the pathogen spreads primarily through infected setts. The present study was undertaken to develop loop-mediated isothermal...

Recovery Plan for Red Leaf Blotch of Soybean Caused by Phoma glycinicola

USDA-ARS?s Scientific Manuscript database

Red leaf blotch (RLB) of soybean is caused by the fungal pathogen Phoma glycinicola, formerly known in the plant pathology literature as Pyrenochaeta glycines, Dactuliophora glycines, and Dactuliochaeata glycines. The disease presently occurs in only a few African countries on soybean and a wild leg...

Paleogene Radiation of a Plant Pathogenic Mushroom

PubMed Central

Coetzee, Martin P. A.; Bloomer, Paulette; Wingfield, Michael J.; Wingfield, Brenda D.

2011-01-01

Background The global movement and speciation of fungal plant pathogens is important, especially because of the economic losses they cause and the ease with which they are able to spread across large areas. Understanding the biogeography and origin of these plant pathogens can provide insights regarding their dispersal and current day distribution. We tested the hypothesis of a Gondwanan origin of the plant pathogenic mushroom genus Armillaria and the currently accepted premise that vicariance accounts for the extant distribution of the species. Methods The phylogeny of a selection of Armillaria species was reconstructed based on Maximum Parsimony (MP), Maximum Likelihood (ML) and Bayesian Inference (BI). A timeline was then placed on the divergence of lineages using a Bayesian relaxed molecular clock approach. Results Phylogenetic analyses of sequenced data for three combined nuclear regions provided strong support for three major geographically defined clades: Holarctic, South American-Australasian and African. Molecular dating placed the initial radiation of the genus at 54 million years ago within the Early Paleogene, postdating the tectonic break-up of Gondwana. Conclusions The distribution of extant Armillaria species is the result of ancient long-distance dispersal rather than vicariance due to continental drift. As these finding are contrary to most prior vicariance hypotheses for fungi, our results highlight the important role of long-distance dispersal in the radiation of fungal pathogens from the Southern Hemisphere. PMID:22216099

Unraveling incompatibility between wheat and the fungal pathogen Zymoseptoria tritici through apoplastic proteomics.

PubMed

Yang, Fen; Li, Wanshun; Derbyshire, Mark; Larsen, Martin R; Rudd, Jason J; Palmisano, Giuseppe

2015-05-08

Hemibiotrophic fungal pathogen Zymoseptoria tritici causes severe foliar disease in wheat. However, current knowledge of molecular mechanisms involved in plant resistance to Z. tritici and Z. tritici virulence factors is far from being complete. The present work investigated the proteome of leaf apoplastic fluid with emphasis on both host wheat and Z. tritici during the compatible and incompatible interactions. The proteomics analysis revealed rapid host responses to the biotrophic growth, including enhanced carbohydrate metabolism, apoplastic defenses and stress, and cell wall reinforcement, might contribute to resistance. Compatibility between the host and the pathogen was associated with inactivated plant apoplastic responses as well as fungal defenses to oxidative stress and perturbation of plant cell wall during the initial biotrophic stage, followed by the strong induction of plant defenses during the necrotrophic stage. To study the role of anti-oxidative stress in Z. tritici pathogenicity in depth, a YAP1 transcription factor regulating antioxidant expression was deleted and showed the contribution to anti-oxidative stress in Z. tritici, but was not required for pathogenicity. This result suggests the functional redundancy of antioxidants in the fungus. The data demonstrate that incompatibility is probably resulted from the proteome-level activation of host apoplastic defenses as well as fungal incapability to adapt to stress and interfere with host cell at the biotrophic stage of the interaction.

Finished Genome of the Fungal Wheat Pathogen Mycosphaerella graminicola Reveals Dispensome Structure, Chromosome Plasticity, and Stealth Pathogenesis

PubMed Central

Ben M'Barek, Sarrah; Dhillon, Braham; Wittenberg, Alexander H. J.; Crane, Charles F.; Hane, James K.; Foster, Andrew J.; Van der Lee, Theo A. J.; Grimwood, Jane; Aerts, Andrea; Antoniw, John; Bailey, Andy; Bluhm, Burt; Bowler, Judith; Bristow, Jim; van der Burgt, Ate; Canto-Canché, Blondy; Churchill, Alice C. L.; Conde-Ferràez, Laura; Cools, Hans J.; Coutinho, Pedro M.; Csukai, Michael; Dehal, Paramvir; De Wit, Pierre; Donzelli, Bruno; van de Geest, Henri C.; van Ham, Roeland C. H. J.; Hammond-Kosack, Kim E.; Henrissat, Bernard; Kilian, Andrzej; Kobayashi, Adilson K.; Koopmann, Edda; Kourmpetis, Yiannis; Kuzniar, Arnold; Lindquist, Erika; Lombard, Vincent; Maliepaard, Chris; Martins, Natalia; Mehrabi, Rahim; Nap, Jan P. H.; Ponomarenko, Alisa; Rudd, Jason J.; Salamov, Asaf; Schmutz, Jeremy; Schouten, Henk J.; Shapiro, Harris; Stergiopoulos, Ioannis; Torriani, Stefano F. F.; Tu, Hank; de Vries, Ronald P.; Waalwijk, Cees; Ware, Sarah B.; Wiebenga, Ad; Zwiers, Lute-Harm; Oliver, Richard P.

2011-01-01

The plant-pathogenic fungus Mycosphaerella graminicola (asexual stage: Septoria tritici) causes septoria tritici blotch, a disease that greatly reduces the yield and quality of wheat. This disease is economically important in most wheat-growing areas worldwide and threatens global food production. Control of the disease has been hampered by a limited understanding of the genetic and biochemical bases of pathogenicity, including mechanisms of infection and of resistance in the host. Unlike most other plant pathogens, M. graminicola has a long latent period during which it evades host defenses. Although this type of stealth pathogenicity occurs commonly in Mycosphaerella and other Dothideomycetes, the largest class of plant-pathogenic fungi, its genetic basis is not known. To address this problem, the genome of M. graminicola was sequenced completely. The finished genome contains 21 chromosomes, eight of which could be lost with no visible effect on the fungus and thus are dispensable. This eight-chromosome dispensome is dynamic in field and progeny isolates, is different from the core genome in gene and repeat content, and appears to have originated by ancient horizontal transfer from an unknown donor. Synteny plots of the M. graminicola chromosomes versus those of the only other sequenced Dothideomycete, Stagonospora nodorum, revealed conservation of gene content but not order or orientation, suggesting a high rate of intra-chromosomal rearrangement in one or both species. This observed “mesosynteny” is very different from synteny seen between other organisms. A surprising feature of the M. graminicola genome compared to other sequenced plant pathogens was that it contained very few genes for enzymes that break down plant cell walls, which was more similar to endophytes than to pathogens. The stealth pathogenesis of M. graminicola probably involves degradation of proteins rather than carbohydrates to evade host defenses during the biotrophic stage of infection and may have evolved from endophytic ancestors. PMID:21695235

Alternative Oxidase in Resistance to Biotic Stresses: Nicotiana attenuata AOX Contributes to Resistance to a Pathogen and a Piercing-Sucking Insect But Not Manduca sexta Larvae1[W][OA

PubMed Central

Zhang, Lu; Oh, Youngjoo; Li, Hongyu; Baldwin, Ian T.; Galis, Ivan

2012-01-01

The role of the alternative respiratory pathway in the protection of plants against biotic stress was examined in transgenic tobacco (Nicotiana attenuata) plants (irAOX) silenced in the expression of ALTERNATIVE OXIDASE (AOX) gene. Wild-type and irAOX plants were independently challenged with (1) chewing herbivores (Manduca sexta), (2) piercing-sucking insects (Empoasca spp.), and (3) bacterial pathogens (Pseudomonas syringae pv tomato DC3000), showing that all these treatments can strongly elicit accumulation of AOX gene transcripts in wild-type plants. When N. attenuata chemical defenses and resistance were examined, irAOX plants showed wild-type levels of defense-related phytohormones, secondary metabolites, and resistance to M. sexta. In contrast, piercing-sucking leafhoppers (Empoasca spp.) caused more leaf damage and induced significantly higher salicylic acid levels in irAOX compared with wild-type plants in the field and/or glasshouse. Subsequently, irAOX plants accumulated lower levels of defense metabolites, 17-hydroxygeranyllinalool diterpene glycosides, caffeoylputrescine, and nicotine compared with wild-type plants under prolonged attack of Empoasca spp. in the glasshouse. Finally, an accelerated cell death phenotype was observed in irAOX plants infected with P. syringae, which correlated with higher levels of salicylic acid and hydrogen peroxide levels in pathogen-infected irAOX compared with wild-type leaves. Overall, the AOX-associated changes in phytohormone and/or redox levels appear to support the resistance of N. attenuata plants against cell piercing-sucking insects and modulate the progression of cell death in pathogen-infected tissues but are not effective against rapidly feeding specialist herbivore M. sexta. PMID:22961128

Characterization and Pathogenicity of New Record of Anthracnose on Various Chili Varieties Caused by Colletotrichum scovillei in Korea.

PubMed

Oo, May Moe; Lim, GiTaek; Jang, Hyun A; Oh, Sang-Keun

2017-09-01

The anthracnose disease caused by Colletotrichum species is well-known as a major plant pathogen that primarily causes fruit rot in pepper and reduces its marketability. Thirty-five isolates representing species of Colletotrichum were obtained from chili fruits showing anthracnose disease symptoms in Chungcheongnam-do and Chungcheongbuk-do, South Korea. These 35 isolates were characterized according to morphological characteristics and nucleotide sequence data of internal transcribed spacer, glyceraldehyde-3-phosphate-dehydrogenase, and β-tubulin. The combined dataset shows that all of these 35 isolates were identified as C. scovillei and morphological characteristics were directly correlated with the nucleotide sequence data. Notably, these isolates were recorded for the first time as the causes of anthracnose caused by C. scovillei on pepper in Korea. Forty cultivars were used to investigate the pathogenicity and to identify the possible source of resistance. The result reveals that all of chili cultivars used in this study are susceptible to C. scovillei .

Characterization and Pathogenicity of New Record of Anthracnose on Various Chili Varieties Caused by Colletotrichum scovillei in Korea

PubMed Central

Oo, May Moe; Lim, GiTaek; Jang, Hyun A

2017-01-01

The anthracnose disease caused by Colletotrichum species is well-known as a major plant pathogen that primarily causes fruit rot in pepper and reduces its marketability. Thirty-five isolates representing species of Colletotrichum were obtained from chili fruits showing anthracnose disease symptoms in Chungcheongnam-do and Chungcheongbuk-do, South Korea. These 35 isolates were characterized according to morphological characteristics and nucleotide sequence data of internal transcribed spacer, glyceraldehyde-3-phosphate-dehydrogenase, and β-tubulin. The combined dataset shows that all of these 35 isolates were identified as C. scovillei and morphological characteristics were directly correlated with the nucleotide sequence data. Notably, these isolates were recorded for the first time as the causes of anthracnose caused by C. scovillei on pepper in Korea. Forty cultivars were used to investigate the pathogenicity and to identify the possible source of resistance. The result reveals that all of chili cultivars used in this study are susceptible to C. scovillei. PMID:29138623

Anthracnose of lucky bamboo Dracaena sanderiana caused by the fungus Colletotrichum dracaenophilum in Egypt.

PubMed

Morsy, Ahmed A; Elshahawy, Ibrahim E

2016-05-01

Dracaena sanderiana, of the family Liliaceae, is among the ornamental plants most frequently imported into Egypt. Typical anthracnose symptoms were observed on the stems of imported D. sanderiana samples. The pathogen was isolated, demonstrated to be pathogenic based on Koch's rule and identified as Colletotrichum dracaenophilum. The optimum temperature for its growth ranges from 25 to 30 °C, maintained for 8 days. Kemazed 50% wettable powder (WP) was the most effective fungicide against the pathogen, as no fungal growth was observed over 100 ppm. The biocontrol agents Trichoderma harzianum and Trichoderma viride followed by Bacillus subtilis and Bacillus pumilus caused the highest reduction in fungal growth. To the best of our knowledge, this report describes the first time that this pathogen was observed on D. sanderiana in Egypt.

Anthracnose of lucky bamboo Dracaena sanderiana caused by the fungus Colletotrichum dracaenophilum in Egypt

PubMed Central

Morsy, Ahmed A.; Elshahawy, Ibrahim E.

2016-01-01

Dracaena sanderiana, of the family Liliaceae, is among the ornamental plants most frequently imported into Egypt. Typical anthracnose symptoms were observed on the stems of imported D. sanderiana samples. The pathogen was isolated, demonstrated to be pathogenic based on Koch’s rule and identified as Colletotrichum dracaenophilum. The optimum temperature for its growth ranges from 25 to 30 °C, maintained for 8 days. Kemazed 50% wettable powder (WP) was the most effective fungicide against the pathogen, as no fungal growth was observed over 100 ppm. The biocontrol agents Trichoderma harzianum and Trichoderma viride followed by Bacillus subtilis and Bacillus pumilus caused the highest reduction in fungal growth. To the best of our knowledge, this report describes the first time that this pathogen was observed on D. sanderiana in Egypt. PMID:27222738

Phytoplasma effector SAP54 induces indeterminate leaf-like flower development in Arabidopsis plants.

PubMed

MacLean, Allyson M; Sugio, Akiko; Makarova, Olga V; Findlay, Kim C; Grieve, Victoria M; Tóth, Réka; Nicolaisen, Mogens; Hogenhout, Saskia A

2011-10-01

Phytoplasmas are insect-transmitted bacterial plant pathogens that cause considerable damage to a diverse range of agricultural crops globally. Symptoms induced in infected plants suggest that these phytopathogens may modulate developmental processes within the plant host. We report herein that Aster Yellows phytoplasma strain Witches' Broom (AY-WB) readily infects the model plant Arabidopsis (Arabidopsis thaliana) ecotype Columbia, inducing symptoms that are characteristic of phytoplasma infection, such as the production of green leaf-like flowers (virescence and phyllody) and increased formation of stems and branches (witches' broom). We found that the majority of genes encoding secreted AY-WB proteins (SAPs), which are candidate effector proteins, are expressed in Arabidopsis and the AY-WB insect vector Macrosteles quadrilineatus (Hemiptera; Cicadellidae). To identify which of these effector proteins induce symptoms of phyllody and virescence, we individually expressed the effector genes in Arabidopsis. From this screen, we have identified a novel AY-WB effector protein, SAP54, that alters floral development, resulting in the production of leaf-like flowers that are similar to those produced by plants infected with this phytoplasma. This study offers novel insight into the effector profile of an insect-transmitted plant pathogen and reports to our knowledge the first example of a microbial pathogen effector protein that targets flower development in a host.

Plant Antimicrobial Peptides as Potential Anticancer Agents

PubMed Central

Guzmán-Rodríguez, Jaquelina Julia; López-Gómez, Rodolfo

2015-01-01

Antimicrobial peptides (AMPs) are part of the innate immune defense mechanism of many organisms and are promising candidates to treat infections caused by pathogenic bacteria to animals and humans. AMPs also display anticancer activities because of their ability to inactivate a wide range of cancer cells. Cancer remains a cause of high morbidity and mortality worldwide. Therefore, the development of methods for its control is desirable. Attractive alternatives include plant AMP thionins, defensins, and cyclotides, which have anticancer activities. Here, we provide an overview of plant AMPs anticancer activities, with an emphasis on their mode of action, their selectivity, and their efficacy. PMID:25815333

Amyloids and prions in plants: Facts and perspectives.

PubMed

Antonets, K S; Nizhnikov, A A

2017-09-03

Amyloids represent protein fibrils that have highly ordered structure with unique physical and chemical properties. Amyloids have long been considered lethal pathogens that cause dozens of incurable diseases in humans and animals. Recent data show that amyloids may not only possess pathogenic properties but are also implicated in the essential biological processes in a variety of prokaryotes and eukaryotes. Functional amyloids have been identified in archaea, bacteria, fungi, and animals, including humans. Plants are one of the most poorly studied groups of organisms in the field of amyloid biology. Although amyloid properties have not been shown under native conditions for any plant protein, studies demonstrating amyloid properties for a set of plant proteins in vitro or in heterologous systems in vivo have been published in recent years. In this review, we systematize the data on the amyloidogenic proteins of plants and their functions and discuss the perspectives of identifying novel amyloids using bioinformatic and proteomic approaches.

Aphid Infestation Increases Fusarium langsethiae and T-2 and HT-2 Mycotoxins in Wheat

PubMed Central

Drakulic, Jassy; Ajigboye, Olubukola; Swarup, Ranjan; Bruce, Toby

2016-01-01

ABSTRACT Fusarium langsethiae is a fungal pathogen of cereal crops that is an increasing problem in northern Europe, but much of its epidemiology is poorly understood. The species produces the mycotoxins T-2 and HT-2, which are highly toxic. It was hypothesized that grain aphids, Sitobion avenae, may transmit F. langsethiae inoculum between wheat plants, and a series of transmission experiments and volatile chemical analyses was performed to test this. Manual translocation of aphids from inoculated to uninfected hosts resulted in pathogen DNA accumulation in hosts. However, the free movement of wingless aphids from infected to healthy plants did not. The addition of winged aphids reared on F. langsethiae-inoculated wheat seedlings to wheat plants also did not achieve successful pathogen transfer. While our data suggested that aphid transmission of the pathogen was not very efficient, we observed an increase in disease when aphids were present. After seedling inoculation, an increase in pathogen DNA accumulation in seedling leaves was observed upon treatment with aphids. Furthermore, the presence of aphids on wheat plants with F. langsethiae-inoculated ears not only led to a rise in the amount of F. langsethiae DNA in infected grain but also to an increase in the concentrations of T-2 and HT-2 toxins, with more than 3-fold higher toxin levels than diseased plants without aphids. This work highlights that aphids increase the susceptibility of wheat host plants to F. langsethiae and that aphid infestation is a risk factor for accumulating increased levels of T-2 and HT-2 in wheat products. IMPORTANCE Fusarium langsethiae is shown here to cause increased contamination levels of grain with toxins produced by fungus when aphids share the host plant. This effect has also recently been demonstrated with Fusarium graminearum, yet the two fungal species show stark differences in their effect on aphid populations. In both cases, aphids improve the ability of the pathogens to cause and initiate Fusarium head blight (FHB) disease in wheat, but F. langsethiae may be able to act as a dispersal agent. F. langsethiae contributes harmful toxins to wheat grain that need to be controlled, but as yet, its epidemiology is unresolved. This work reveals insights into the role aphids play in promoting the successful colonization of this species in wheat and the benefit of controlling aphid populations on crops that are at high risk of FHB. PMID:27590814

Diversifying selection in the wheat stem rust fungus acts predominantly on pathogen-associated gene families and reveals candidate effectors

PubMed Central

Sperschneider, Jana; Ying, Hua; Dodds, Peter N.; Gardiner, Donald M.; Upadhyaya, Narayana M.; Singh, Karam B.; Manners, John M.; Taylor, Jennifer M.

2014-01-01

Plant pathogens cause severe losses to crop plants and threaten global food production. One striking example is the wheat stem rust fungus, Puccinia graminis f. sp. tritici, which can rapidly evolve new virulent pathotypes in response to resistant host lines. Like several other filamentous fungal and oomycete plant pathogens, its genome features expanded gene families that have been implicated in host-pathogen interactions, possibly encoding effector proteins that interact directly with target host defense proteins. Previous efforts to understand virulence largely relied on the prediction of secreted, small and cysteine-rich proteins as candidate effectors and thus delivered an overwhelming number of candidates. Here, we implement an alternative analysis strategy that uses the signal of adaptive evolution as a line of evidence for effector function, combined with comparative information and expression data. We demonstrate that in planta up-regulated genes that are rapidly evolving are found almost exclusively in pathogen-associated gene families, affirming the impact of host-pathogen co-evolution on genome structure and the adaptive diversification of specialized gene families. In particular, we predict 42 effector candidates that are conserved only across pathogens, induced during infection and rapidly evolving. One of our top candidates has recently been shown to induce genotype-specific hypersensitive cell death in wheat. This shows that comparative genomics incorporating the evolutionary signal of adaptation is powerful for predicting effector candidates for laboratory verification. Our system can be applied to a wide range of pathogens and will give insight into host-pathogen dynamics, ultimately leading to progress in strategies for disease control. PMID:25225496

Characterization of bacterial knot disease caused by Pseudomonas savastanoi pv. savastanoi on pomegranate (Punica granatum L.) trees: a new host of the pathogen.

PubMed

Bozkurt, I A; Soylu, S; Mirik, M; Ulubas Serce, C; Baysal, Ö

2014-11-01

This study aimed to isolate and identify the causal organism causing hyperplastic outgrowths (knots) on stems and branches of pomegranate trees in the Eastern Mediterranean region of Turkey. Bacterial colonies were isolated from young knots on plates containing selective nutrient media. Biochemical tests, fatty acid analysis and PCR were performed to identify possible causal disease agent. Representative isolates were identified as Pseudomonas.pv.savastanoi (Psv) using biochemical tests, fatty acid profiling and PCR. Following inoculation of pomegranate plants (cv. hicaz) with bacterial suspensions, 25 of 54 bacterial isolates caused typical knots at the site of inoculation. PCR analysis, using specific primer for Psv, generated a single amplicon from all isolates. The similarity of the sequence of Turkish pomegranate isolate was 99% similar to the corresponding gene sequences of Psv in the databases. Based on symptoms, biochemical, molecular, pathogenicity tests and sequence analyses, the disease agent of knots observed on the pomegranate trees is Psv. To the best of our knowledge, this research has revealed pomegranate as a natural host of Psv, which extends the list of host plant species affected by the pathogen in the world and Turkey. Pomegranate trees were affected by the disease with outgrowths (galls or knot) disease. Currently, there is no published study on disease agent(s) causing the galls or knots on pomegranate trees in worldwide. Bacterial colonies were isolated from young knots. The causal agent of the knot Pseudomonas savastanoi pv.savastanoi (Psv) was identified based on symptoms, biochemical, molecular methods, pathogenicity tests and sequence analysis. To the best of our knowledge, this is the first report of Psv on pomegranate as a natural host, which extends the growing list of plant species affected by this bacterium in the world and Turkey. © 2014 The Society for Applied Microbiology.

Albugo-imposed changes to tryptophan-derived antimicrobial metabolite biosynthesis may contribute to suppression of non-host resistance to Phytophthora infestans in Arabidopsis thaliana.

PubMed

Prince, David C; Rallapalli, Ghanasyam; Xu, Deyang; Schoonbeek, Henk-Jan; Çevik, Volkan; Asai, Shuta; Kemen, Eric; Cruz-Mireles, Neftaly; Kemen, Ariane; Belhaj, Khaoula; Schornack, Sebastian; Kamoun, Sophien; Holub, Eric B; Halkier, Barbara A; Jones, Jonathan D G

2017-03-20

Plants are exposed to diverse pathogens and pests, yet most plants are resistant to most plant pathogens. Non-host resistance describes the ability of all members of a plant species to successfully prevent colonization by any given member of a pathogen species. White blister rust caused by Albugo species can overcome non-host resistance and enable secondary infection and reproduction of usually non-virulent pathogens, including the potato late blight pathogen Phytophthora infestans on Arabidopsis thaliana. However, the molecular basis of host defense suppression in this complex plant-microbe interaction is unclear. Here, we investigate specific defense mechanisms in Arabidopsis that are suppressed by Albugo infection. Gene expression profiling revealed that two species of Albugo upregulate genes associated with tryptophan-derived antimicrobial metabolites in Arabidopsis. Albugo laibachii-infected tissue has altered levels of these metabolites, with lower indol-3-yl methylglucosinolate and higher camalexin accumulation than uninfected tissue. We investigated the contribution of these Albugo-imposed phenotypes to suppression of non-host resistance to P. infestans. Absence of tryptophan-derived antimicrobial compounds enables P. infestans colonization of Arabidopsis, although to a lesser extent than Albugo-infected tissue. A. laibachii also suppresses a subset of genes regulated by salicylic acid; however, salicylic acid plays only a minor role in non-host resistance to P. infestans. Albugo sp. alter tryptophan-derived metabolites and suppress elements of the responses to salicylic acid in Arabidopsis. Albugo sp. imposed alterations in tryptophan-derived metabolites may play a role in Arabidopsis non-host resistance to P. infestans. Understanding the basis of non-host resistance to pathogens such as P. infestans could assist in development of strategies to elevate food security.

Genome analysis of the foxtail millet pathogen Sclerospora graminicola reveals the complex effector repertoire of graminicolous downy mildews.

PubMed

Kobayashi, Michie; Hiraka, Yukie; Abe, Akira; Yaegashi, Hiroki; Natsume, Satoshi; Kikuchi, Hideko; Takagi, Hiroki; Saitoh, Hiromasa; Win, Joe; Kamoun, Sophien; Terauchi, Ryohei

2017-11-22

Downy mildew, caused by the oomycete pathogen Sclerospora graminicola, is an economically important disease of Gramineae crops including foxtail millet (Setaria italica). Plants infected with S. graminicola are generally stunted and often undergo a transformation of flower organs into leaves (phyllody or witches' broom), resulting in serious yield loss. To establish the molecular basis of downy mildew disease in foxtail millet, we carried out whole-genome sequencing and an RNA-seq analysis of S. graminicola. Sequence reads were generated from S. graminicola using an Illumina sequencing platform and assembled de novo into a draft genome sequence comprising approximately 360 Mbp. Of this sequence, 73% comprised repetitive elements, and a total of 16,736 genes were predicted from the RNA-seq data. The predicted genes included those encoding effector-like proteins with high sequence similarity to those previously identified in other oomycete pathogens. Genes encoding jacalin-like lectin-domain-containing secreted proteins were enriched in S. graminicola compared to other oomycetes. Of a total of 1220 genes encoding putative secreted proteins, 91 significantly changed their expression levels during the infection of plant tissues compared to the sporangia and zoospore stages of the S. graminicola lifecycle. We established the draft genome sequence of a downy mildew pathogen that infects Gramineae plants. Based on this sequence and our transcriptome analysis, we generated a catalog of in planta-induced candidate effector genes, providing a solid foundation from which to identify the effectors causing phyllody.

Altered distribution of susceptibility phenotypes implies environmental modulation of genetic resistance

Treesearch

Thomas R. Gordon; Neil McRoberts

2012-01-01

Resistance to disease is determined by the genetic capacity of a plant to recognize and respond to a pathogen, as modified to varying degrees by the environment in which the interaction occurs. Physical factors such as temperature and moisture can limit the ability of a pathogen to infect and cause disease, and may also influence the response of the host through...

RNA-Seq analysis of resistant and susceptible sub-tropical maize lines reveals a role for kauralexins in resistance to grey leaf spot disease, caused by Cercospora zeina

USDA-ARS?s Scientific Manuscript database

Cercospora zeina is a foliar pathogen responsible for maize grey leaf spot in southern Africa that negatively impacts maize production. Plants use a variety of chemical and structural mechanisms to defend themselves against invading pathogens such as C. zeina, including the production of secondary m...

Forest stand dynamics and sudden oak death: Mortality in mixed-evergreen forests dominated by coast live oak

Treesearch

L.B. Brown; B. Allen-Diaz

2009-01-01

Sudden oak death (SOD), caused by the recently discovered non-native invasive pathogen, Phytophthora ramorum, has already killed tens of thousands of native coast live oak and tanoak trees in California. Little is known of potential short and long term impacts of this novel plant–pathogen interaction on forest structure and composition. Coast live...

A race for survival: Can Bromus tectorum seeds escape Pyrenophora semeniperda-caused mortality by germinating quickly?

Treesearch

Julie Beckstead; Susan E. Meyer; Cherrilyn J. Molder; Caitlyn Smith

2007-01-01

Pathogen-seed interactions may involve a race for seed resources, so that seeds that germinate more quickly, mobilizing reserves, will be more likely to escape seed death than slow-germinating seeds. This race-for-survival hypothesis was tested for the North American seed pathogen Pyrenophora semeniperda on seeds of the annual grass Bromus tectorum, an invasive plant...

Erwinia carotovora elicitors and Botrytis cinerea activate defense responses in Physcomitrella patens

PubMed Central

Ponce de León, Inés; Oliver, Juan Pablo; Castro, Alexandra; Gaggero, Carina; Bentancor, Marcel; Vidal, Sabina

2007-01-01

Background Vascular plants respond to pathogens by activating a diverse array of defense mechanisms. Studies with these plants have provided a wealth of information on pathogen recognition, signal transduction and the activation of defense responses. However, very little is known about the infection and defense responses of the bryophyte, Physcomitrella patens, to well-studied phytopathogens. The purpose of this study was to determine: i) whether two representative broad host range pathogens, Erwinia carotovora ssp. carotovora (E.c. carotovora) and Botrytis cinerea (B. cinerea), could infect Physcomitrella, and ii) whether B. cinerea, elicitors of a harpin (HrpN) producing E.c. carotovora strain (SCC1) or a HrpN-negative strain (SCC3193), could cause disease symptoms and induce defense responses in Physcomitrella. Results B. cinerea and E.c. carotovora were found to readily infect Physcomitrella gametophytic tissues and cause disease symptoms. Treatments with B. cinerea spores or cell-free culture filtrates from E.c. carotovoraSCC1 (CF(SCC1)), resulted in disease development with severe maceration of Physcomitrella tissues, while CF(SCC3193) produced only mild maceration. Although increased cell death was observed with either the CFs or B. cinerea, the occurrence of cytoplasmic shrinkage was only visible in Evans blue stained protonemal cells treated with CF(SCC1) or inoculated with B. cinerea. Most cells showing cytoplasmic shrinkage accumulated autofluorescent compounds and brown chloroplasts were evident in a high proportion of these cells. CF treatments and B. cinerea inoculation induced the expression of the defense-related genes: PR-1, PAL, CHS and LOX. Conclusion B. cinerea and E.c. carotovora elicitors induce a defense response in Physcomitrella, as evidenced by enhanced expression of conserved plant defense-related genes. Since cytoplasmic shrinkage is the most common morphological change observed in plant PCD, and that harpins and B. cinerea induce this type of cell death in vascular plants, our results suggest that E.c. carotovora CFSCC1 containing HrpN and B. cinerea could also induce this type of cell death in Physcomitrella. Our studies thus establish Physcomitrella as an experimental host for investigation of plant-pathogen interactions and B. cinerea and elicitors of E.c. carotovora as promising tools for understanding the mechanisms involved in defense responses and in pathogen-mediated cell death in this simple land plant. PMID:17922917

Draft Genome Sequence of Highly Virulent Race 4/Biovar 3 of Ralstonia solanacearum CaRs_Mep Causing Bacterial Wilt in Zingiberaceae Plants in India.

PubMed

Kumar, Aundy; Munjal, Vibhuti; Sheoran, Neelam; Prameela, Thekkan Puthiyaveedu; Suseelabhai, Rajamma; Aggarwal, Rashmi; Jain, Rakesh Kumar; Eapen, Santhosh J

2017-01-05

The genome of Ralstonia solanacearum CaRs_Mep, a race 4/biovar 3/phylotype I bacterium causing wilt in small cardamom and other Zingiberaceae plants, was sequenced. Analysis of the 5.7-Mb genome sequence will aid in better understanding of the genetic determinants of host range, host jump, survival, pathogenicity, and virulence of race 4 of R. solanacearum. Copyright © 2017 Kumar et al.

First Report of Sclerotium Rot on Cymbidium Orchids Caused by Sclerotium rolfsii in Korea

PubMed Central

Lee, Seong-Chan; Lee, Jung-Sup; Soh, Jae-Woo; Kim, Su

2012-01-01

Sclerotium rot was found on Cymbidium orchids at Seosan-si, Chungcheongnam-do, Korea, in July, 2010. Symptoms occurred on low leaves, which turned yellowish, after which the entire plant wilted. Severely infected plants were blighted and eventually died. White mycelial mats and sclerotia appeared on pseudobulbs. Based on the mycological characteristics and pathogenicity, the causal fungus was identified as Sclerotium rolfsii. This is the first report of new Sclerotium rot on Cymbidium spp. caused by S. rolfsii in Korea. PMID:23323053

Bipolaris microstegii

Treesearch

Andrew M. Minnis; Amy Y. Rossman; Nathan M. Kleczewski; S. Luke. Flory

2012-01-01

Many species of Bipolaris are important pathogens of grasses. This new species was isolated from Microstegium vimineum, an invasive plant in the USA. The fungus causes disease on Microstegium, but it also infects a wider range of hosts.

Biocontrol potential of Trichoderma harzianum isolate T-aloe against Sclerotinia sclerotiorum in soybean.

PubMed

Zhang, Fuli; Ge, Honglian; Zhang, Fan; Guo, Ning; Wang, Yucheng; Chen, Long; Ji, Xiue; Li, Chengwei

2016-03-01

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum (Lib.) de Bary is a major disease of soybean (Glycine max (L.) Merr.). At present, we revealed the three-way interaction between Trichoderma harzianum T-aloe, pathogen S. sclerotiorum and soybean plants in order to demonstrate biocontrol mechanism and evaluate biocontrol potential of T-aloe against S. sclerotiorum in soybean. In our experiments, T-aloe inhibited the growth of S. sclerotiorum with an efficiency of 56.3% in dual culture tests. T-aloe hyphae grew in parallel or intertwined with S. sclerotiorum hyphae and produced hooked contact branches, indicating mycoparasitism. Plate tests showed that T-aloe culture filtrate inhibited S. sclerotiorum growth with an inhibition efficiency of 51.2% and sclerotia production. T-aloe pretreatment showed growth-promoting effect on soybean plants. The activities of peroxidase, superoxide dismutase, and catalase increased, and the hydrogen peroxide (H2O2) as well as the superoxide radical (O2(-)) content in soybean leaves decreased after T-aloe pretreatment in response to S. sclerotiorum pathogen challenge. T-aloe treatment diminished damage caused by pathogen stress on soybean leaf cell membrane, and increased chlorophyll as well as total phenol contents. The defense-related genes PR1, PR2, and PR3 were expressed in the leaves of T-aloe-treated plants. In summary, T-aloe displayed biocontrol potential against S. sclerotiorum. This is the first report of unraveling biocontrol potential of Trichoderma Spp. to soybean sclerotinia stem rot from the three-way interaction between the biocontrol agent, pathogen S. sclerotiorum and soybean plants. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

Cloning, purification, crystallization and 1.57 Å resolution X-ray data analysis of AmsI, the tyrosine phosphatase controlling amylovoran biosynthesis in the plant pathogen Erwinia amylovora.

PubMed

Benini, Stefano; Caputi, Lorenzo; Cianci, Michele

2014-12-01

The Gram-negative bacterium Erwinia amylovora is a destructive pathogen of plants belonging to the Rosaceae family. Amongst its pathogenicity factors, E. amylovora produces the exopolysaccharide amylovoran, which contributes to the occlusion of plant vessels, causing wilting of shoots and eventually resulting in plant death. Amylovoran biosynthesis requires the presence of 12 genes (from amsA to amsL) clustered in the ams region of the E. amylovora genome. They mostly encode glycosyl transferases (AmsG, AmsB, AmsD, AmsE, AmsJ and AmsK), proteins involved in amylovoran translocation and assembly (AmsH, AmsL and AmsC), and also a tyrosine kinase (AmsA) and a tyrosine phosphatase (AmsI), which are both involved in the regulation of amylovoran biosynthesis. The low-molecular-weight protein tyrosine phosphatase AmsI was overexpressed as a His6-tagged protein in Escherichia coli, purified and crystallized. X-ray diffraction data were collected to a maximum resolution of 1.57 Å in space group P3121.

Activation of Pathogenesis-related Genes by the Rhizobacterium, Bacillus sp. JS, Which Induces Systemic Resistance in Tobacco Plants.

PubMed

Kim, Ji-Seong; Lee, Jeongeun; Lee, Chan-Hui; Woo, Su Young; Kang, Hoduck; Seo, Sang-Gyu; Kim, Sun-Hyung

2015-06-01

Plant growth promoting rhizobacteria (PGPR) are known to confer disease resistance to plants. Bacillus sp. JS demonstrated antifungal activities against five fungal pathogens in in vitro assays. To verify whether the volatiles of Bacillus sp. JS confer disease resistance, tobacco leaves pre-treated with the volatiles were damaged by the fungal pathogen, Rhizoctonia solani and oomycete Phytophthora nicotianae. Pre-treated tobacco leaves had smaller lesion than the control plant leaves. In pathogenesis-related (PR) gene expression analysis, volatiles of Bacillus sp. JS caused the up-regulation of PR-2 encoding β-1,3-glucanase and acidic PR-3 encoding chitinase. Expression of acidic PR-4 encoding chitinase and acidic PR-9 encoding peroxidase increased gradually after exposure of the volatiles to Bacillus sp. JS. Basic PR-14 encoding lipid transfer protein was also increased. However, PR-1 genes, as markers of salicylic acid (SA) induced resistance, were not expressed. These results suggested that the volatiles of Bacillus sp. JS confer disease resistance against fungal and oomycete pathogens through PR genes expression.

Signals of Systemic Immunity in Plants: Progress and Open Questions

PubMed Central

Ádám, Attila L.; Nagy, Zoltán Á.; Kátay, György; Mergenthaler, Emese; Viczián, Orsolya

2018-01-01

Systemic acquired resistance (SAR) is a defence mechanism that induces protection against a wide range of pathogens in distant, pathogen-free parts of plants after a primary inoculation. Multiple mobile compounds were identified as putative SAR signals or important factors for influencing movement of SAR signalling elements in Arabidopsis and tobacco. These include compounds with very different chemical structures like lipid transfer protein DIR1 (DEFECTIVE IN INDUCED RESISTANCE1), methyl salicylate (MeSA), dehydroabietinal (DA), azelaic acid (AzA), glycerol-3-phosphate dependent factor (G3P) and the lysine catabolite pipecolic acid (Pip). Genetic studies with different SAR-deficient mutants and silenced lines support the idea that some of these compounds (MeSA, DIR1 and G3P) are activated only when SAR is induced in darkness. In addition, although AzA doubled in phloem exudate of tobacco mosaic virus (TMV) infected tobacco leaves, external AzA treatment could not induce resistance neither to viral nor bacterial pathogens, independent of light conditions. Besides light intensity and timing of light exposition after primary inoculation, spectral distribution of light could also influence the SAR induction capacity. Recent data indicated that TMV and CMV (cucumber mosaic virus) infection in tobacco, like bacteria in Arabidopsis, caused massive accumulation of Pip. Treatment of tobacco leaves with Pip in the light, caused a drastic and significant local and systemic decrease in lesion size of TMV infection. Moreover, two very recent papers, added in proof, demonstrated the role of FMO1 (FLAVIN-DEPENDENT-MONOOXYGENASE1) in conversion of Pip to N-hydroxypipecolic acid (NHP). NHP systemically accumulates after microbial attack and acts as a potent inducer of plant immunity to bacterial and oomycete pathogens in Arabidopsis. These results argue for the pivotal role of Pip and NHP as an important signal compound of SAR response in different plants against different pathogens. PMID:29642641

Effect of flooding on root and foliar disease severity on Rhododendron Caused by Phytophthora ramorum

Treesearch

Niklaus J. Grünwald; Megan Kitner; Robert G. Linderman

2008-01-01

It is generally thought that extensive periods of flooding can predispose plants to infection by Phytophthora pathogens. We evaluated the effect of 0, 1, 3, and 7 days of flooding before infection of Rhododendron plants through either wound inoculation of leaves or infestation of the potting mix using two hybrid cultivars ?...

Effects of Phytophthora ramorum on volatile organic compound emissions of Rhododendron using gas chromatography-mass spectrometry

USDA-ARS?s Scientific Manuscript database

Phytophthora ramorum is an invasive and devastating plant pathogen that causes sudden oak death in coastal forests in the western United States and ramorum blight in nursery ornamentals and native plants in various landscapes. As a broad host-range quarantine pest that can be asymptomatic in some ho...

Use of micro-CT to elucidate details of the anatomy and feeding of the Asian citrus psyllid Diaphorina citri Kuwayama, 1908 (Insecta: Hemiptera, Liviidae)

USDA-ARS?s Scientific Manuscript database

Huanglongbing (HLB), also known as citrus greening disease, is caused by plant-infecting bacteria. The most prominent pathogen within the Americas: United States of America, Mexico, and Brazil, is Candidatus Liberibacter asiaticus, which affects plants of the Family: Rutaceae, in particularly citrus...

Gene discovery in EST sequences from the wheat leaf rust fungus puccinia triticina sexual spores, asexual spores and haustoria, compared to other rust and corn smut fungi

USDA-ARS?s Scientific Manuscript database

Background: Rust fungi are biotrophic basidiomycete plant pathogens that cause major diseases on plants and trees world-wide, affecting agriculture and forestry. Their biotrophic nature precludes many established molecular genetic manipulations and lines of research. The generation of genomic resour...

Metabolomics and Cheminformatics Analysis of Antifungal Function of Plant Metabolites

PubMed Central

Cuperlovic-Culf, Miroslava; Rajagopalan, NandhaKishore; Tulpan, Dan; Loewen, Michele C.

2016-01-01

Fusarium head blight (FHB), primarily caused by Fusarium graminearum, is a devastating disease of wheat. Partial resistance to FHB of several wheat cultivars includes specific metabolic responses to inoculation. Previously published studies have determined major metabolic changes induced by pathogens in resistant and susceptible plants. Functionality of the majority of these metabolites in resistance remains unknown. In this work we have made a compilation of all metabolites determined as selectively accumulated following FHB inoculation in resistant plants. Characteristics, as well as possible functions and targets of these metabolites, are investigated using cheminformatics approaches with focus on the likelihood of these metabolites acting as drug-like molecules against fungal pathogens. Results of computational analyses of binding properties of several representative metabolites to homology models of fungal proteins are presented. Theoretical analysis highlights the possibility for strong inhibitory activity of several metabolites against some major proteins in Fusarium graminearum, such as carbonic anhydrases and cytochrome P450s. Activity of several of these compounds has been experimentally confirmed in fungal growth inhibition assays. Analysis of anti-fungal properties of plant metabolites can lead to the development of more resistant wheat varieties while showing novel application of cheminformatics approaches in the analysis of plant/pathogen interactions. PMID:27706030

Sharing a Host Plant (Wheat [Triticum aestivum]) Increases the Fitness of Fusarium graminearum and the Severity of Fusarium Head Blight but Reduces the Fitness of Grain Aphids (Sitobion avenae)

PubMed Central

Drakulic, Jassy; Caulfield, John; Woodcock, Christine; Jones, Stephen P. T.; Linforth, Robert; Bruce, Toby J. A.

2015-01-01

We hypothesized that interactions between fusarium head blight-causing pathogens and herbivores are likely to occur because they share wheat as a host plant. Our aim was to investigate the interactions between the grain aphid, Sitobion avenae, and Fusarium graminearum on wheat ears and the role that host volatile chemicals play in mediating interactions. Wheat ears were treated with aphids and F. graminearum inoculum, together or separately, and disease progress was monitored by visual assessment and by quantification of pathogen DNA and mycotoxins. Plants exposed to both aphids and F. graminearum inoculum showed accelerated disease progression, with a 2-fold increase in disease severity and 5-fold increase in mycotoxin accumulation over those of plants treated only with F. graminearum. Furthermore, the longer the period of aphid colonization of the host prior to inoculation with F. graminearum, the greater the amount of pathogen DNA that accumulated. Headspace samples of plant volatiles were collected for use in aphid olfactometer assays and were analyzed by gas chromatography-mass spectrometry (GC-MS) and GC-coupled electroantennography. Disease-induced plant volatiles were repellent to aphids, and 2-pentadecanone was the key semiochemical underpinning the repellent effect. We measured aphid survival and fecundity on infected wheat ears and found that both were markedly reduced on infected ears. Thus, interactions between F. graminearum and grain aphids on wheat ears benefit the pathogen at the expense of the pest. Our findings have important consequences for disease epidemiology, because we show increased spread and development of host disease, together with greater disease severity and greater accumulation of pathogen DNA and mycotoxin, when aphids are present. PMID:25769834

Sharing a Host Plant (Wheat [Triticum aestivum]) Increases the Fitness of Fusarium graminearum and the Severity of Fusarium Head Blight but Reduces the Fitness of Grain Aphids (Sitobion avenae).

PubMed

Drakulic, Jassy; Caulfield, John; Woodcock, Christine; Jones, Stephen P T; Linforth, Robert; Bruce, Toby J A; Ray, Rumiana V

2015-05-15

We hypothesized that interactions between fusarium head blight-causing pathogens and herbivores are likely to occur because they share wheat as a host plant. Our aim was to investigate the interactions between the grain aphid, Sitobion avenae, and Fusarium graminearum on wheat ears and the role that host volatile chemicals play in mediating interactions. Wheat ears were treated with aphids and F. graminearum inoculum, together or separately, and disease progress was monitored by visual assessment and by quantification of pathogen DNA and mycotoxins. Plants exposed to both aphids and F. graminearum inoculum showed accelerated disease progression, with a 2-fold increase in disease severity and 5-fold increase in mycotoxin accumulation over those of plants treated only with F. graminearum. Furthermore, the longer the period of aphid colonization of the host prior to inoculation with F. graminearum, the greater the amount of pathogen DNA that accumulated. Headspace samples of plant volatiles were collected for use in aphid olfactometer assays and were analyzed by gas chromatography-mass spectrometry (GC-MS) and GC-coupled electroantennography. Disease-induced plant volatiles were repellent to aphids, and 2-pentadecanone was the key semiochemical underpinning the repellent effect. We measured aphid survival and fecundity on infected wheat ears and found that both were markedly reduced on infected ears. Thus, interactions between F. graminearum and grain aphids on wheat ears benefit the pathogen at the expense of the pest. Our findings have important consequences for disease epidemiology, because we show increased spread and development of host disease, together with greater disease severity and greater accumulation of pathogen DNA and mycotoxin, when aphids are present. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

The Arabidopsis microtubule-associated protein MAP65-3 supports infection by filamentous biotrophic pathogens by down-regulating salicylic acid-dependent defenses.

PubMed

Quentin, Michaël; Baurès, Isabelle; Hoefle, Caroline; Caillaud, Marie-Cécile; Allasia, Valérie; Panabières, Franck; Abad, Pierre; Hückelhoven, Ralph; Keller, Harald; Favery, Bruno

2016-03-01

The oomycete Hyaloperonospora arabidopsidis and the ascomycete Erysiphe cruciferarum are obligate biotrophic pathogens causing downy mildew and powdery mildew, respectively, on Arabidopsis. Upon infection, the filamentous pathogens induce the formation of intracellular bulbous structures called haustoria, which are required for the biotrophic lifestyle. We previously showed that the microtubule-associated protein AtMAP65-3 plays a critical role in organizing cytoskeleton microtubule arrays during mitosis and cytokinesis. This renders the protein essential for the development of giant cells, which are the feeding sites induced by root knot nematodes. Here, we show that AtMAP65-3 expression is also induced in leaves upon infection by the downy mildew oomycete and the powdery mildew fungus. Loss of AtMAP65-3 function in the map65-3 mutant dramatically reduced infection by both pathogens, predominantly at the stages of leaf penetration. Whole-transcriptome analysis showed an over-represented, constitutive activation of genes involved in salicylic acid (SA) biosynthesis, signaling, and defense execution in map65-3, whereas jasmonic acid (JA)-mediated signaling was down-regulated. Preventing SA synthesis and accumulation in map65-3 rescued plant susceptibility to pathogens, but not the developmental phenotype caused by cytoskeleton defaults. AtMAP65-3 thus has a dual role. It positively regulates cytokinesis, thus plant growth and development, and negatively interferes with plant defense against filamentous biotrophs. Our data suggest that downy mildew and powdery mildew stimulate AtMAP65-3 expression to down-regulate SA signaling for infection. © The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Comparative genomics of a cannabis pathogen reveals insight into the evolution of pathogenicity in Xanthomonas

PubMed Central

Jacobs, Jonathan M.; Pesce, Céline; Lefeuvre, Pierre; Koebnik, Ralf

2015-01-01

Pathogenic bacteria in the genus Xanthomonas cause diseases on over 350 plant species, including cannabis (Cannabis sativa L.). Because of regulatory limitations, the biology of the Xanthomonas-cannabis pathosystem remains largely unexplored. To gain insight into the evolution of Xanthomonas strains pathogenic to cannabis, we sequenced the genomes of two geographically distinct Xanthomonas strains, NCPPB 3753 and NCPPB 2877, which were previously isolated from symptomatic plant tissue in Japan and Romania. Comparative multilocus sequence analysis of housekeeping genes revealed that they belong to Group 2, which comprises most of the described species of Xanthomonas. Interestingly, both strains lack the Hrp Type III secretion system and do not contain any of the known Type III effectors. Yet their genomes notably encode two key Hrp pathogenicity regulators HrpG and HrpX, and hrpG and hrpX are in the same genetic organization as in the other Group 2 xanthomonads. Promoter prediction of HrpX-regulated genes suggests the induction of an aminopeptidase, a lipase and two polygalacturonases upon plant colonization, similar to other plant-pathogenic xanthomonads. Genome analysis of the distantly related Xanthomonas maliensis strain 97M, which was isolated from a rice leaf in Mali, similarly demonstrated the presence of HrpG, HrpX, and a HrpX-regulated polygalacturonase, and the absence of the Hrp Type III secretion system and known Type III effectors. Given the observation that some Xanthomonas strains across distinct taxa do not contain hrpG and hrpX, we speculate a stepwise evolution of pathogenicity, which involves (i) acquisition of key regulatory genes and cell wall-degrading enzymes, followed by (ii) acquisition of the Hrp Type III secretion system, which is ultimately accompanied by (iii) successive acquisition of Type III effectors. PMID:26136759

Nonhost resistance to rust pathogens - a continuation of continua.

PubMed

Bettgenhaeuser, Jan; Gilbert, Brian; Ayliffe, Michael; Moscou, Matthew J

2014-01-01

The rust fungi (order: Pucciniales) are a group of widely distributed fungal plant pathogens, which can infect representatives of all vascular plant groups. Rust diseases significantly impact several crop species and considerable research focuses on understanding the basis of host specificity and nonhost resistance. Like many pathogens, rust fungi vary considerably in the number of hosts they can infect, such as wheat leaf rust (Puccinia triticina), which can only infect species in the genera Triticum and Aegilops, whereas Asian soybean rust (Phakopsora pachyrhizi) is known to infect over 95 species from over 42 genera. A greater understanding of the genetic basis determining host range has the potential to identify sources of durable resistance for agronomically important crops. Delimiting the boundary between host and nonhost has been complicated by the quantitative nature of phenotypes in the transition between these two states. Plant-pathogen interactions in this intermediate state are characterized either by (1) the majority of accessions of a species being resistant to the rust or (2) the rust only being able to partially complete key components of its life cycle. This leads to a continuum of disease phenotypes in the interaction with different plant species, observed as a range from compatibility (host) to complete immunity within a species (nonhost). In this review we will highlight how the quantitative nature of disease resistance in these intermediate interactions is caused by a continuum of defense barriers, which a pathogen needs to overcome for successfully establishing itself in the host. To illustrate continua as this underlying principle, we will discuss the advances that have been made in studying nonhost resistance towards rust pathogens, particularly cereal rust pathogens.

The Powdery Mildew Disease of Arabidopsis: A Paradigm for the Interaction between Plants and Biotrophic Fungi

PubMed Central

Micali, Cristina; Göllner, Katharina; Humphry, Matt; Consonni, Chiara; Panstruga, Ralph

2008-01-01

The powdery mildew diseases, caused by fungal species of the Erysiphales, have an important economic impact on a variety of plant species and have driven basic and applied research efforts in the field of phytopathology for many years. Although the first taxonomic reports on the Erysiphales date back to the 1850's, advances into the molecular biology of these fungal species have been hampered by their obligate biotrophic nature and difficulties associated with their cultivation and genetic manipulation in the laboratory. The discovery in the 1990's of a few species of powdery mildew fungi that cause disease on Arabidopsis has opened a new chapter in this research field. The great advantages of working with a model plant species have translated into remarkable progress in our understanding of these complex pathogens and their interaction with the plant host. Herein we summarize advances in the study of Arabidopsis-powdery mildew interactions and discuss their implications for the general field of plant pathology. We provide an overview of the life cycle of the pathogens on Arabidopsis and describe the structural and functional changes that occur during infection in the host and fungus in compatible and incompatible interactions, with special emphasis on defense signaling, resistance pathways, and compatibility factors. Finally, we discuss the future of powdery mildew research in anticipation of the sequencing of multiple powdery mildew genomes. The cumulative body of knowledge on powdery mildews of Arabidopsis provides a valuable tool for the study and understanding of disease associated with many other obligate biotrophic pathogen species. PMID:22303240

Comparative transcript profiling by SuperSAGE identifies novel candidate genes for controlling potato quantitative resistance to late blight not compromised by late maturity.

PubMed

Draffehn, Astrid M; Li, Li; Krezdorn, Nicolas; Ding, Jia; Lübeck, Jens; Strahwald, Josef; Muktar, Meki S; Walkemeier, Birgit; Rotter, Björn; Gebhardt, Christiane

2013-01-01

Resistance to pathogens is essential for survival of wild and cultivated plants. Pathogen susceptibility causes major losses of crop yield and quality. Durable field resistance combined with high yield and other superior agronomic characters are therefore, important objectives in every crop breeding program. Precision and efficacy of resistance breeding can be enhanced by molecular diagnostic tools, which result from knowledge of the molecular basis of resistance and susceptibility. Breeding uses resistance conferred by single R genes and polygenic quantitative resistance. The latter is partial but considered more durable. Molecular mechanisms of plant pathogen interactions are elucidated mainly in experimental systems involving single R genes, whereas most genes important for quantitative resistance in crops like potato are unknown. Quantitative resistance of potato to Phytophthora infestans causing late blight is often compromised by late plant maturity, a negative agronomic character. Our objective was to identify candidate genes for quantitative resistance to late blight not compromised by late plant maturity. We used diagnostic DNA-markers to select plants with different field levels of maturity corrected resistance (MCR) to late blight and compared their leaf transcriptomes before and after infection with P. infestans using SuperSAGE (serial analysis of gene expression) technology and next generation sequencing. We identified 2034 transcripts up or down regulated upon infection, including a homolog of the kiwi fruit allergen kiwellin. 806 transcripts showed differential expression between groups of genotypes with contrasting MCR levels. The observed expression patterns suggest that MCR is in part controlled by differential transcript levels in uninfected plants. Functional annotation suggests that, besides biotic and abiotic stress responses, general cellular processes such as photosynthesis, protein biosynthesis, and degradation play a role in MCR.

Pseudomonas protegens Pf-5 causes discoloration and pitting of mushroom caps due to the production of antifungal metabolites

USDA-ARS?s Scientific Manuscript database

Bacteria in the diverse P. fluorescens group include mushroom pathogens, such as Pseudomonas tolaasii, and rhizosphere inhabitants known for their antifungal metabolite production and biological control of plant disease, such as Pseudomonas protegens Pf-5. Here, we report that strain Pf-5 causes bro...

Inter-chromosomal transfer of immune regulation during infection of barley with the powdery mildew pathogen

USDA-ARS?s Scientific Manuscript database

Powdery mildews infect over 9,500 plant species, causing critical yield loss. Powdery mildew disease of barley is caused by the Ascomycete fungus, Blumeria graminis f. sp. hordei (Bgh) and has become a model for the interactions among obligate biotrophs and their cereal hosts. Successful infection r...

Effect of Sugarcane Mosaic caused by Sorghum mosaic virus on sugarcane in Louisiana

USDA-ARS?s Scientific Manuscript database

Sugarcane mosaic is caused by two viruses, Sugarcane mosaic virus (SCVM) or Sorghum mosaic virus (SrMV). In Louisiana, SrMV is the predominant mosaic pathogen affecting sugarcane. In a field experiment established in 2012, plots were planted with seed cane with or without mosaic symptoms. The mosaic...

Ongoing molecular studies of Eucalyptus powdery mildew in Brazil

Treesearch

N. R. Fonseca; L. M. S. Guimaraes; R. P. Pires; Ned Klopfenstein; M. -S. Kim; A. C. Alfenas

2016-01-01

Powdery mildew diseases are caused by biotrophic fungi in the Erysiphales. These fungal pathogens are easily observed by the whitish powdery appearance caused by their colonization of the aerial surfaces on living plants (Stadnik & Rivera, 2001) (Figure 1). In Brazil, powdery mildew of Eucalyptus spp is increasing under the current nursery production...

Determining the risk of Phytophthora ramorum spread from nurseries via waterways

Treesearch

Marianne Elliott; Gary Chastagner; Katie Coats; Gil Dermott

2013-01-01

Phytophthora ramorum, the fungus-like pathogen which causes sudden oak death, is a threat to the Pacific Northwest nursery industry. Because this is a quarantine organism, the destruction of plants and mitigation treatments resulting from a positive P. ramorum detection has caused millions of dollars in losses to the commercial...

Two whole genome sequences of Xylella fastidiosa (strains M12 and M23) causing almond leaf scorch disease in California

USDA-ARS?s Scientific Manuscript database

Xylella fastidiosa is a Gram negative, nutritionally fastidious plant pathogenic bacterium that causes many economically important diseases including almond leaf scorch disease (ALSD) and Pierce’s disease of grape in California, as well as citrus variegated chlorosis in South America. Genome inform...

Effects of damping-off caused by Rhizoctonia solani anastomosis group 2-1 on roots of wheat and oil seed rape quantified using X-ray Computed Tomography and real-time PCR

PubMed Central

Sturrock, Craig J.; Woodhall, James; Brown, Matthew; Walker, Catherine; Mooney, Sacha J.; Ray, Rumiana V.

2015-01-01

Rhizoctonia solani is a plant pathogenic fungus that causes significant establishment and yield losses to several important food crops globally. This is the first application of high resolution X-ray micro Computed Tomography (X-ray μCT) and real-time PCR to study host–pathogen interactions in situ and elucidate the mechanism of Rhizoctonia damping-off disease over a 6-day period caused by R. solani, anastomosis group (AG) 2-1 in wheat (Triticum aestivum cv. Gallant) and oil seed rape (OSR, Brassica napus cv. Marinka). Temporal, non-destructive analysis of root system architectures was performed using RooTrak and validated by the destructive method of root washing. Disease was assessed visually and related to pathogen DNA quantification in soil using real-time PCR. R. solani AG2-1 at similar initial DNA concentrations in soil was capable of causing significant damage to the developing root systems of both wheat and OSR. Disease caused reductions in primary root number, root volume, root surface area, and convex hull which were affected less in the monocotyledonous host. Wheat was more tolerant to the pathogen, exhibited fewer symptoms and developed more complex root systems. In contrast, R. solani caused earlier damage and maceration of the taproot of the dicot, OSR. Disease severity was related to pathogen DNA accumulation in soil only for OSR, however, reductions in root traits were significantly associated with both disease and pathogen DNA. The method offers the first steps in advancing current understanding of soil-borne pathogen behavior in situ at the pore scale, which may lead to the development of mitigation measures to combat disease influence in the field. PMID:26157449

Effects of damping-off caused by Rhizoctonia solani anastomosis group 2-1 on roots of wheat and oil seed rape quantified using X-ray Computed Tomography and real-time PCR.

PubMed

Sturrock, Craig J; Woodhall, James; Brown, Matthew; Walker, Catherine; Mooney, Sacha J; Ray, Rumiana V

2015-01-01

Rhizoctonia solani is a plant pathogenic fungus that causes significant establishment and yield losses to several important food crops globally. This is the first application of high resolution X-ray micro Computed Tomography (X-ray μCT) and real-time PCR to study host-pathogen interactions in situ and elucidate the mechanism of Rhizoctonia damping-off disease over a 6-day period caused by R. solani, anastomosis group (AG) 2-1 in wheat (Triticum aestivum cv. Gallant) and oil seed rape (OSR, Brassica napus cv. Marinka). Temporal, non-destructive analysis of root system architectures was performed using RooTrak and validated by the destructive method of root washing. Disease was assessed visually and related to pathogen DNA quantification in soil using real-time PCR. R. solani AG2-1 at similar initial DNA concentrations in soil was capable of causing significant damage to the developing root systems of both wheat and OSR. Disease caused reductions in primary root number, root volume, root surface area, and convex hull which were affected less in the monocotyledonous host. Wheat was more tolerant to the pathogen, exhibited fewer symptoms and developed more complex root systems. In contrast, R. solani caused earlier damage and maceration of the taproot of the dicot, OSR. Disease severity was related to pathogen DNA accumulation in soil only for OSR, however, reductions in root traits were significantly associated with both disease and pathogen DNA. The method offers the first steps in advancing current understanding of soil-borne pathogen behavior in situ at the pore scale, which may lead to the development of mitigation measures to combat disease influence in the field.

Entomopathogenicity to Two Hemipteran Insects Is Common but Variable across Epiphytic Pseudomonas syringae Strains.

PubMed

Smee, Melanie R; Baltrus, David A; Hendry, Tory A

2017-01-01

Strains of the well-studied plant pathogen Pseudomonas syringae show large differences in their ability to colonize plants epiphytically and to inflict damage to hosts. Additionally, P. syringae can infect some sap-sucking insects and at least one P. syringae strain is highly virulent to insects, causing death to most individuals within as few as 4 days and growing to high population densities within insect hosts. The likelihood of agricultural pest insects coming into contact with transient populations of P. syringae while feeding on plants is high, yet the ecological implications of these interactions are currently not well understood as virulence has not been tested across a wide range of strains. To investigate virulence differences across strains we exposed the sweet potato whitefly, Bemisia tabaci , and the pea aphid, Acyrthosiphon pisum , both of which are cosmopolitan agricultural pests, to 12 P. syringae strains. We used oral inoculations with bacteria suspended in artificial diet in order to assay virulence while controlling for other variables such as differences in epiphytic growth ability. Generally, patterns of pathogenicity remain consistent across the two species of hemipteran insects, with bacterial strains from phylogroup II, or genomospecies 1, causing the highest rate of mortality with up to 86% of individuals dead after 72 h post infection. The rate of mortality is highly variable across strains, some significantly different from negative control treatments and others showing no discernable difference. Interestingly, one of the most pathogenic strains to both aphids and whiteflies (Cit7) is thought to be non-pathogenic on plants. We also found Cit7 to establish the highest epiphytic population after 48 h on fava beans. Between the nine P. syringae strains tested for epiphytic ability there is also much variation, but epiphytic ability was positively correlated with pathogenicity to insects, suggesting that the two traits may be linked and that strains likely to be found on plants may often be entomopathogenic. Our study highlights that there may be a use for epiphytic bacteria in the biological control of insect crop pests. It also suggests that interactions with epiphytic bacteria could be evolutionary and ecological drivers for hemipteran insects.

Effect of chitosan on hyphal growth and spore germination of plant pathogenic and biocontrol fungi.

PubMed

Palma-Guerrero, J; Jansson, H-B; Salinas, J; Lopez-Llorca, L V

2008-02-01

To investigate the toxic effect of chitosan on important root pathogenic and biocontrol fungi (nematophagous, entomopathogenic and mycoparasitic). We have used standard bioassays to investigate the effect of chitosan on colony growth and developed bioassays to test spore germination. The results showed that the root pathogenic and mycoparasitic fungi tested were more sensitive to chitosan than nematophagous and entomopathogenic fungi. Chitosanases (and perhaps related enzymes) are involved in the resistance to chitosan. Two fungi, one sensitive to chitosan, Fusarium oxysporum f. sp. radicis-lycopersici, and one less sensitive, Pochonia chlamydosporia, were selected for ultrastructural investigations. Transmission electron microscopy revealed differences in the ultrastructural alterations caused by chitosan in the spores of the plant pathogenic fungus and in those of the nematophagous fungus. Confocal laser microscopy showed that Rhodamine-labelled chitosan enters rapidly into conidia of both fungi, in an energy-dependent process. Nematophagous and entomopathogenic fungi are rather resistant to the toxic effect of chitosan. Resistance of nematophagous and entomopathogenic fungi to chitosan could be associated with their high extracellular chitosanolytic activity. Furthermore, ultrastructural damage is much more severe in the chitosan sensitive fungus. The results of this paper suggest that biocontrol fungi tested could be combined with chitosan for biological control of plant pathogens and pests.

Disease Interactions in a Shared Host Plant: Effects of Pre-Existing Viral Infection on Cucurbit Plant Defense Responses and Resistance to Bacterial Wilt Disease

PubMed Central

Mauck, Kerry E.; Pulido, Hannier; De Moraes, Consuelo M.; Stephenson, Andrew G.; Mescher, Mark C.

2013-01-01

Both biotic and abiotic stressors can elicit broad-spectrum plant resistance against subsequent pathogen challenges. However, we currently have little understanding of how such effects influence broader aspects of disease ecology and epidemiology in natural environments where plants interact with multiple antagonists simultaneously. In previous work, we have shown that healthy wild gourd plants (Cucurbita pepo ssp. texana) contract a fatal bacterial wilt infection (caused by Erwinia tracheiphila) at significantly higher rates than plants infected with Zucchini yellow mosaic virus (ZYMV). We recently reported evidence that this pattern is explained, at least in part, by reduced visitation of ZYMV-infected plants by the cucumber beetle vectors of E. tracheiphila. Here we examine whether ZYMV-infection may also directly elicit plant resistance to subsequent E. tracheiphila infection. In laboratory studies, we assayed the induction of key phytohormones (SA and JA) in single and mixed infections of these pathogens, as well as in response to the feeding of A. vittatum cucumber beetles on healthy and infected plants. We also tracked the incidence and progression of wilt disease symptoms in plants with prior ZYMV infections. Our results indicate that ZYMV-infection slightly delays the progression of wilt symptoms, but does not significantly reduce E. tracheiphila infection success. This observation supports the hypothesis that reduced rates of wilt disease in ZYMV-infected plants reflect reduced visitation by beetle vectors. We also documented consistently strong SA responses to ZYMV infection, but limited responses to E. tracheiphila in the absence of ZYMV, suggesting that the latter pathogen may effectively evade or suppress plant defenses, although we observed no evidence of antagonistic cross-talk between SA and JA signaling pathways. We did, however, document effects of E. tracheiphila on induced responses to herbivory that may influence host-plant quality for (and hence pathogen acquisition by) cucumber beetles. PMID:24155951

Management of invading pathogens should be informed by epidemiology rather than administrative boundaries.

PubMed

Thompson, Robin N; Cobb, Richard C; Gilligan, Christopher A; Cunniffe, Nik J

2016-03-24

Plant and animal disease outbreaks have significant ecological and economic impacts. The spatial extent of control is often informed solely by administrative geography - for example, quarantine of an entire county or state once an invading disease is detected - with little regard for pathogen epidemiology. We present a stochastic model for the spread of a plant pathogen that couples spread in the natural environment and transmission via the nursery trade, and use it to illustrate that control deployed according to administrative boundaries is almost always sub-optimal. We use sudden oak death (caused by Phytophthora ramorum ) in mixed forests in California as motivation for our study, since the decision as to whether or not to deploy plant trade quarantine is currently undertaken on a county-by-county basis for that system. However, our key conclusion is applicable more generally: basing management of any disease entirely upon administrative borders does not balance the cost of control with the possible economic and ecological costs of further spread in the optimal fashion.

A family of conserved bacterial effectors inhibits salicylic acid-mediated basal immunity and promotes disease necrosis in plants.

PubMed

DebRoy, Sruti; Thilmony, Roger; Kwack, Yong-Bum; Nomura, Kinya; He, Sheng Yang

2004-06-29

Salicylic acid (SA)-mediated host immunity plays a central role in combating microbial pathogens in plants. Inactivation of SA-mediated immunity, therefore, would be a critical step in the evolution of a successful plant pathogen. It is known that mutations in conserved effector loci (CEL) in the plant pathogens Pseudomonas syringae (the Delta CEL mutation), Erwinia amylovora (the dspA/E mutation), and Pantoea stewartii subsp. stewartii (the wtsE mutation) exert particularly strong negative effects on bacterial virulence in their host plants by unknown mechanisms. We found that the loss of virulence in Delta CEL and dspA/E mutants was linked to their inability to suppress cell wall-based defenses and to cause normal disease necrosis in Arabidopsis and apple host plants. The Delta CEL mutant activated SA-dependent callose deposition in wild-type Arabidopsis but failed to elicit high levels of callose-associated defense in Arabidopsis plants blocked in SA accumulation or synthesis. This mutant also multiplied more aggressively in SA-deficient plants than in wild-type plants. The hopPtoM and avrE genes in the CEL of P. syringae were found to encode suppressors of this SA-dependent basal defense. The widespread conservation of the HopPtoM and AvrE families of effectors in various bacteria suggests that suppression of SA-dependent basal immunity and promotion of host cell death are important virulence strategies for bacterial infection of plants.

The Pathogen-Host Interactions database (PHI-base): additions and future developments

PubMed Central

Urban, Martin; Pant, Rashmi; Raghunath, Arathi; Irvine, Alistair G.; Pedro, Helder; Hammond-Kosack, Kim E.

2015-01-01

Rapidly evolving pathogens cause a diverse array of diseases and epidemics that threaten crop yield, food security as well as human, animal and ecosystem health. To combat infection greater comparative knowledge is required on the pathogenic process in multiple species. The Pathogen-Host Interactions database (PHI-base) catalogues experimentally verified pathogenicity, virulence and effector genes from bacterial, fungal and protist pathogens. Mutant phenotypes are associated with gene information. The included pathogens infect a wide range of hosts including humans, animals, plants, insects, fish and other fungi. The current version, PHI-base 3.6, available at http://www.phi-base.org, stores information on 2875 genes, 4102 interactions, 110 host species, 160 pathogenic species (103 plant, 3 fungal and 54 animal infecting species) and 181 diseases drawn from 1243 references. Phenotypic and gene function information has been obtained by manual curation of the peer-reviewed literature. A controlled vocabulary consisting of nine high-level phenotype terms permits comparisons and data analysis across the taxonomic space. PHI-base phenotypes were mapped via their associated gene information to reference genomes available in Ensembl Genomes. Virulence genes and hotspots can be visualized directly in genome browsers. Future plans for PHI-base include development of tools facilitating community-led curation and inclusion of the corresponding host target(s). PMID:25414340

Comparative Genomics Yields Insights into Niche Adaptation of Plant Vascular Wilt Pathogens

PubMed Central

Klosterman, Steven J.; Subbarao, Krishna V.; Kang, Seogchan; Veronese, Paola; Gold, Scott E.; Thomma, Bart P. H. J.; Chen, Zehua; Henrissat, Bernard; Lee, Yong-Hwan; Park, Jongsun; Garcia-Pedrajas, Maria D.; Barbara, Dez J.; Anchieta, Amy; de Jonge, Ronnie; Santhanam, Parthasarathy; Maruthachalam, Karunakaran; Atallah, Zahi; Amyotte, Stefan G.; Paz, Zahi; Inderbitzin, Patrik; Hayes, Ryan J.; Heiman, David I.; Young, Sarah; Zeng, Qiandong; Engels, Reinhard; Galagan, James; Cuomo, Christina A.; Dobinson, Katherine F.; Ma, Li-Jun

2011-01-01

The vascular wilt fungi Verticillium dahliae and V. albo-atrum infect over 200 plant species, causing billions of dollars in annual crop losses. The characteristic wilt symptoms are a result of colonization and proliferation of the pathogens in the xylem vessels, which undergo fluctuations in osmolarity. To gain insights into the mechanisms that confer the organisms' pathogenicity and enable them to proliferate in the unique ecological niche of the plant vascular system, we sequenced the genomes of V. dahliae and V. albo-atrum and compared them to each other, and to the genome of Fusarium oxysporum, another fungal wilt pathogen. Our analyses identified a set of proteins that are shared among all three wilt pathogens, and present in few other fungal species. One of these is a homolog of a bacterial glucosyltransferase that synthesizes virulence-related osmoregulated periplasmic glucans in bacteria. Pathogenicity tests of the corresponding V. dahliae glucosyltransferase gene deletion mutants indicate that the gene is required for full virulence in the Australian tobacco species Nicotiana benthamiana. Compared to other fungi, the two sequenced Verticillium genomes encode more pectin-degrading enzymes and other carbohydrate-active enzymes, suggesting an extraordinary capacity to degrade plant pectin barricades. The high level of synteny between the two Verticillium assemblies highlighted four flexible genomic islands in V. dahliae that are enriched for transposable elements, and contain duplicated genes and genes that are important in signaling/transcriptional regulation and iron/lipid metabolism. Coupled with an enhanced capacity to degrade plant materials, these genomic islands may contribute to the expanded genetic diversity and virulence of V. dahliae, the primary causal agent of Verticillium wilts. Significantly, our study reveals insights into the genetic mechanisms of niche adaptation of fungal wilt pathogens, advances our understanding of the evolution and development of their pathogenesis, and sheds light on potential avenues for the development of novel disease management strategies to combat destructive wilt diseases. PMID:21829347

A preliminary bioclimatic approach to predicting potential distribution of Phellinus noxious and geographical areas at risk from invasion

Treesearch

Ned B. Klopfenstein; Eric W. I. Pitman; John W. Hanna; Phil G. Cannon; Jane E. Stewart; Norio Sahashi; Yuko Ota; Tsutomu Hattori; Mitsuteru Akiba; Louise Shuey; Robert L. Schlub; Fred Brooks; Ndeme Atibalentja; Alvin M. C. Tang; Regent Y. C. Lam; Mike W. K. Leung; L. M. Chu; H. S. Kwan; Mohd Farid bin Ahmad; Su See Lee; Hsin-Han Lee; Jyh-Nong Tsai; Yu-Ching Huang; Chia-Lin Chung; Ruey-Fen Liou; Mee-Sook Kim

2016-01-01

Phellinus noxius, the cause of brown root-rot disease, is an invasive pathogen that was first described by Corner in Singapore (Corner 1932). It has a wide host range of primarily woody plants representing over 200 species from diverse families (Ann et al. 2002). This pathogen is also widespread, and has been reported to occur in many tropical/subtropical...

Phytohormone mediation of interactions between herbivores and plant pathogens.

PubMed

Lazebnik, Jenny; Frago, Enric; Dicke, Marcel; van Loon, Joop J A

2014-07-01

Induced plant defenses against either pathogens or herbivore attackers are regulated by phytohormones. These phytohormones are increasingly recognized as important mediators of interactions between organisms associated with plants. In this review, we discuss the role of plant defense hormones in sequential tri-partite interactions among plants, pathogenic microbes, and herbivorous insects, based on the most recent literature. We discuss the importance of pathogen trophic strategy in the interaction with herbivores that exhibit different feeding modes. Plant resistance mechanisms also affect plant quality in future interactions with attackers. We discuss exemplary evidence for the hypotheses that (i) biotrophic pathogens can facilitate chewing herbivores, unless plants exhibit effector-triggered immunity, but (ii) facilitate or inhibit phloem feeders. (iii) Necrotrophic pathogens, on the other hand, can inhibit both phloem feeders and chewers. We also propose herbivore feeding mode as predictor of effects on pathogens of different trophic strategies, providing evidence for the hypotheses that (iv) phloem feeders inhibit pathogen attack by increasing SA induction, whereas (v) chewing herbivores tend not to affect necrotrophic pathogens, while they may either inhibit or facilitate biotrophic pathogens. Putting these hypotheses to the test will increase our understanding of phytohormonal regulation of plant defense to sequential attack by plant pathogens and insect herbivores. This will provide valuable insight into plant-mediated ecological interactions among members of the plant-associated community.

Interrelationships of food safety and plant pathology: the life cycle of human pathogens on plants.

PubMed

Barak, Jeri D; Schroeder, Brenda K

2012-01-01

Bacterial food-borne pathogens use plants as vectors between animal hosts, all the while following the life cycle script of plant-associated bacteria. Similar to phytobacteria, Salmonella, pathogenic Escherichia coli, and cross-domain pathogens have a foothold in agricultural production areas. The commonality of environmental contamination translates to contact with plants. Because of the chronic absence of kill steps against human pathogens for fresh produce, arrival on plants leads to persistence and the risk of human illness. Significant research progress is revealing mechanisms used by human pathogens to colonize plants and important biological interactions between and among bacteria in planta. These findings articulate the difficulty of eliminating or reducing the pathogen from plants. The plant itself may be an untapped key to clean produce. This review highlights the life of human pathogens outside an animal host, focusing on the role of plants, and illustrates areas that are ripe for future investigation.

In Vivo Study of Trichoderma-Pathogen-Plant Interactions, Using Constitutive and Inducible Green Fluorescent Protein Reporter Systems

PubMed Central

Lu, Zexun; Tombolini, Riccardo; Woo, Sheridan; Zeilinger, Susanne; Lorito, Matteo; Jansson, Janet K.

2004-01-01

Plant tissue colonization by Trichoderma atroviride plays a critical role in the reduction of diseases caused by phytopathogenic fungi, but this process has not been thoroughly studied in situ. We monitored in situ interactions between gfp-tagged biocontrol strains of T. atroviride and soilborne plant pathogens that were grown in cocultures and on cucumber seeds by confocal scanning laser microscopy and fluorescence stereomicroscopy. Spores of T. atroviride adhered to Pythium ultimum mycelia in coculture experiments. In mycoparasitic interactions of T. atroviride with P. ultimum or Rhizoctonia solani, the mycoparasitic hyphae grew alongside the pathogen mycelia, and this was followed by coiling and formation of specialized structures similar to hooks, appressoria, and papillae. The morphological changes observed depended on the pathogen tested. Branching of T. atroviride mycelium appeared to be an active response to the presence of the pathogenic host. Mycoparasitism of P. ultimum by T. atroviride occurred on cucumber seed surfaces while the seeds were germinating. The interaction of these fungi on the cucumber seeds was similar to the interaction observed in coculture experiments. Green fluorescent protein expression under the control of host-inducible promoters was also studied. The induction of specific Trichoderma genes was monitored visually in cocultures, on plant surfaces, and in soil in the presence of colloidal chitin or Rhizoctonia by confocal microscopy and fluorescence stereomicroscopy. These tools allowed initiation of the mycoparasitic gene expression cascade to be monitored in vivo. PMID:15128569

Concurrent Drought Stress and Vascular Pathogen Infection Induce Common and Distinct Transcriptomic Responses in Chickpea

PubMed Central

Sinha, Ranjita; Gupta, Aarti; Senthil-Kumar, Muthappa

2017-01-01

Chickpea (Cicer arietinum); the second largest legume grown worldwide is prone to drought and various pathogen infections. These drought and pathogen stresses often occur concurrently in the field conditions. However, the molecular events in response to that are largely unknown. The present study examines the transcriptome dynamics in chickpea plants exposed to a combination of water-deficit stress and Ralstonia solanacearum infection. R. solanacearum is a potential wilt disease causing pathogen in chickpea. Drought stressed chickpea plants were infected with this pathogen and the plants were allowed to experience progressive drought with 2 and 4 days of R. solanacearum infection called short duration stress (SD stresses) and long duration stress (LD stresses), respectively. Our study showed that R. solanacearum multiplication decreased under SD-combined stress compared to SD-pathogen but there was no significant change in LD-combined stress compared to LD-pathogen. The microarray analysis during these conditions showed that 821 and 1039 differentially expressed genes (DEGs) were unique to SD- and LD-combined stresses, respectively, when compared with individual stress conditions. Three and fifteen genes were common among all the SD-stress treatments and LD-stress treatments, respectively. Genes involved in secondary cell wall biosynthesis, alkaloid biosynthesis, defense related proteins, and osmo-protectants were up-regulated during combined stress. The expression of genes involved in lignin and cellulose biosynthesis were specifically up-regulated in SD-combined, LD-combined, and LD-pathogen stress. A close transcriptomic association of LD-pathogen stress with SD-combined stress was observed in this study which indicates that R. solanacearum infection also exerts drought stress along with pathogen stress thus mimics combined stress effect. Furthermore the expression profiling of candidate genes using real-time quantitative PCR validated the microarray data. The study showed that down-regulation of defense-related genes during LD-combined stress resulted in an increased bacterial multiplication as compared to SD-combined stress. Overall, our study highlights a sub-set of DEGs uniquely expressed in response to combined stress, which serve as potential candidates for further functional characterization to delineate the molecular response of the plant to concurrent drought-pathogen stress. PMID:28382041

Transcriptome analysis of sweet orange trees infected with 'Candidatus Liberibacter asiaticus' and two strains of Citrus Tristeza Virus.

PubMed

Fu, Shimin; Shao, Jonathan; Zhou, Changyong; Hartung, John S

2016-05-11

Huanglongbing (HLB) and tristeza, are diseases of citrus caused by a member of the α-proteobacteria, 'Candidatus Liberibacter asiaticus' (CaLas), and Citrus tristeza virus (CTV) respectively. HLB is a devastating disease, but CTV strains vary from very severe to very mild. Both CaLas and CTV are phloem-restricted. The CaLas-B232 strain and CTV-B6 cause a wide range of severe and similar symptoms. The mild strain CTV-B2 doesn't induce significant symptoms or damage to plants. Transcriptome profiles obtained through RNA-seq revealed 611, 404 and 285 differentially expressed transcripts (DETs) after infection with CaLas-B232, CTV-B6 and CTV-B2. These DETs were components of a wide range of pathways involved in circadian rhythm, cell wall modification and cell organization, as well as transcription factors, transport, hormone response and secondary metabolism, signaling and stress response. The number of transcripts that responded to both CTV-B6 and CaLas-B232 was much larger than the number of transcripts that responded to both strains of CTV or to both CTV-B2 and CaLas-B232. A total of 38 genes were assayed by RT-qPCR and the correlation coefficients between Gfold and RT-qPCR were 0.82, 0.69, 0.81 for sweet orange plants infected with CTV-B2, CTV-B6 and CaLas-B232, respectively. The number and composition of DETs reflected the complexity of symptoms caused by the pathogens in established infections, although the leaf tissues sampled were asymptomatic. There were greater similarities between the sweet orange in response to CTV-B6 and CaLas-B232 than between the two CTV strains, reflecting the similar physiological changes caused by both CTV-B6 and CaLas-B232. The circadian rhythm system of plants was perturbed by all three pathogens, especially by CTV-B6, and the ion balance was also disrupted by all three pathogens, especially by CaLas-B232. Defense responses related to cell wall modification, transcriptional regulation, hormones, secondary metabolites, kinases and stress were activated by all three pathogens but with different patterns. The transcriptome profiles of Citrus sinensis identified host genes whose expression is affected by the presence of a pathogen in the phloem without producing symptoms (CTV-B2), and host genes whose expression leads to induction of symptoms in the plant (CTV-B6, CaLas-B232).

Ecology, Epidemiology and Disease Management of Ralstonia syzygii in Indonesia.

PubMed

Safni, Irda; Subandiyah, Siti; Fegan, Mark

2018-01-01

Ralstonia solanacearum species complex phylotype IV strains, which have been primarily isolated from Indonesia, Australia, Japan, Korea, and Malaysia, have undergone recent taxonomic and nomenclatural changes to be placed in the species Ralstonia syzygii . This species contains three subspecies; Ralstonia syzygii subsp. syzygii , a pathogen causing Sumatra disease of clove trees in Indonesia, Ralstonia syzygii subsp. indonesiensis , the causal pathogen of bacterial wilt disease on a wide range of host plants, and Ralstonia syzygii subsp. celebesensis , the causal pathogen of blood disease on Musa spp. In Indonesia, these three subspecies have devastated the cultivation of susceptible host plants which have high economic value. Limited knowledge on the ecology and epidemiology of the diseases has hindered the development of effective control strategies. In this review, we provide insights into the ecology, epidemiology and disease control of these three subspecies of Ralstonia syzygii .

Expression of green fluorescent protein in Xylella fastidiosa is affected by passage through host plants.

PubMed

Qin, Xiaoting; Hartung, John S

2004-09-01

Xylella fastidiosa, a Gram-negative bacterial plant pathogen, causes Pierce's disease of grapevine in North America. In South America the pathogen causes citrus variegated chlorosis, which is widespread in Brazil. We have introduced into Xylella fastidiosa a mini-Tn5 transposon that encodes a green fluorescent protein (GFP) gene optimized for expression in bacteria. The mini-Tn5 derivative was inserted into different sites of the genome in independent transconjugants as determined by Southern blotting. The GFP gene was expressed well and to different levels in different transconjugants. Four independent transconjugants were separately used to inoculate sweet orange and tobacco seedlings. The transconjugants were able to colonize the plants and were subsequently isolated from points distal to the inoculation sites. When the relative fluorescence of the transconjugants that had been passed through either tobacco or sweet orange was compared with that of the same transconjugant maintained continuously in vitro, we observed that passage through either plant host significantly increased the level of expression of the GFP. The increased level of expression of GFP was transient, and was lost upon further culture in vitro. Xylella fastidiosa forms biofilms in planta which are believed to represent a metabolically differentiated state. The increased expression of GFP observed after passage through plants may be accounted for by this phenomenon.

Transposon mutagenesis of Xylella fastidiosa by electroporation of Tn5 synaptic complexes.

PubMed

Guilhabert, M R; Hoffman, L M; Mills, D A; Kirkpatrick, B C

2001-06-01

Pierce's disease, a lethal disease of grapevine, is caused by Xylella fastidiosa, a gram-negative, xylem-limited bacterium that is transmitted from plant to plant by xylem-feeding insects. Strains of X. fastidiosa also have been associated with diseases that cause tremendous losses in many other economically important plants, including citrus. Although the complete genome sequence of X. fastidiosa has recently been determined, the inability to transform or produce transposon mutants of X. fastidiosa has been a major impediment to understanding pathogen-, plant-, and insect-vector interactions. We evaluated the ability of four different suicide vectors carrying either Tn5 or Tn10 transposons as well as a preformed Tn5 transposase-transposon synaptic complex (transposome) to transpose X. fastidiosa. The four suicide vectors failed to produce any detectable transposition events. Electroporation of transposomes, however, yielded 6 x 10(3) and 4 x 10(3) Tn5 mutants per microg of DNA in two different grapevine strains of X. fastidiosa. Molecular analysis showed that the transposition insertions were single, independent, stable events. Sequence analysis of the Tn5 insertion sites indicated that the transpositions occur randomly in the X. fastidiosa genome. Transposome-mediated mutagenesis should facilitate the identification of X. fastidiosa genes that mediate plant pathogenicity and insect transmission.

Comparative Proteomic Analysis of Different Isolates of Fusarium oxysporum f.sp. lycopersici to Exploit the Differentially Expressed Proteins Responsible for Virulence on Tomato Plants

PubMed Central

Manikandan, Rajendran; Harish, Sankarasubramanian; Karthikeyan, Gandhi; Raguchander, Thiruvengadam

2018-01-01

The vascular wilt of tomato caused by Fusarium oxysporum f.sp. lycopersici is an important soil borne pathogen causes severe yield loss. The molecular characterization and their interaction with its host is necessary to develop a protection strategy. 20 isolates of F. oxysporum f.sp. lycopersici (FOL) were isolated from wilt infected tomato plants across Tamil Nadu. They were subjected to cultural, morphological, molecular and virulence studies. The results revealed that all the isolates produced both micro and macro conidia with different size, number of cells. The colors of the culture and growth pattern were also varied. In addition, chlamydospores were observed terminally and intercalary. The PCR analysis with F. oxysporum species-specific primer significantly amplified an amplicon of 600 bp fragment in all the isolates. Based on the above characters and pathogenicity, isolate FOL-8 was considered as virulent and FOL-20 was considered as least virulent. Proteomics strategy was adopted to determine the virulence factors between the isolates of FOL-8 and FOL-20. The 2D analyses have showed the differential expression of 17 different proteins. Among them, three proteins were down regulated and 14 proteins were significantly up regulated in FOL-8 than FOL-20 isolate. Among the 17 proteins, 10 distinct spots were analyzed by MALDI-TOF. The functions of the analyzed proteins, suggested that they were involved in pathogenicity, symptom expression and disease development, sporulation, growth, and higher penetration rate on tomato root tissue. Overall, these experiments proves the role of proteome in pathogenicity of F. oxysporum f.sp. lycopersici in tomato and unravels the mechanism behinds the virulence of the pathogen in causing wilt disease. PMID:29559969

Greasy tactics in the plant-pathogen molecular arms race.

PubMed

Boyle, Patrick C; Martin, Gregory B

2015-03-01

The modification of proteins by the attachment of fatty acids is a targeting tactic involved in mechanisms of both plant immunity and bacterial pathogenesis. The plant plasma membrane (PM) is a key battleground in the war against disease-causing microbes. This membrane is armed with an array of sensor proteins that function as a surveillance system to detect invading pathogens. Several of these sensor proteins are directed to the plasma membrane through the covalent addition of fatty acids, a process termed fatty acylation. Phytopathogens secrete effector proteins into the plant cell to subvert these surveillance mechanisms, rendering the host susceptible to infection. The targeting of effectors to specific locales within plant cells, particularly the internal face of the host PM, is critical for their virulence function. Several bacterial effectors hijack the host fatty acylation machinery to be modified and directed to this contested locale. To find and fight these fatty acylated effectors the plant leverages lipid-modified intracellular sensors. This review provides examples featuring how fatty acylation is a battle tactic used by both combatants in the molecular arms race between plants and pathogens. Also highlighted is the exploitation of a specific form of host-mediated fatty acid modification, which appears to be exclusively employed by phytopathogenic effector proteins. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Phytoplasma Effector SAP54 Induces Indeterminate Leaf-Like Flower Development in Arabidopsis Plants1[C][W][OA

PubMed Central

MacLean, Allyson M.; Sugio, Akiko; Makarova, Olga V.; Findlay, Kim C.; Grieve, Victoria M.; Tóth, Réka; Nicolaisen, Mogens; Hogenhout, Saskia A.

2011-01-01

Phytoplasmas are insect-transmitted bacterial plant pathogens that cause considerable damage to a diverse range of agricultural crops globally. Symptoms induced in infected plants suggest that these phytopathogens may modulate developmental processes within the plant host. We report herein that Aster Yellows phytoplasma strain Witches’ Broom (AY-WB) readily infects the model plant Arabidopsis (Arabidopsis thaliana) ecotype Columbia, inducing symptoms that are characteristic of phytoplasma infection, such as the production of green leaf-like flowers (virescence and phyllody) and increased formation of stems and branches (witches’ broom). We found that the majority of genes encoding secreted AY-WB proteins (SAPs), which are candidate effector proteins, are expressed in Arabidopsis and the AY-WB insect vector Macrosteles quadrilineatus (Hemiptera; Cicadellidae). To identify which of these effector proteins induce symptoms of phyllody and virescence, we individually expressed the effector genes in Arabidopsis. From this screen, we have identified a novel AY-WB effector protein, SAP54, that alters floral development, resulting in the production of leaf-like flowers that are similar to those produced by plants infected with this phytoplasma. This study offers novel insight into the effector profile of an insect-transmitted plant pathogen and reports to our knowledge the first example of a microbial pathogen effector protein that targets flower development in a host. PMID:21849514

Production of Xylella fastidiosa diffusible signal factor in transgenic grape causes pathogen confusion and reduction in severity of Pierce's disease.

PubMed

Lindow, Steven; Newman, Karyn; Chatterjee, Subhadeep; Baccari, Clelia; Lavarone, Anthony T; Ionescu, Michael

2014-03-01

The rpfF gene from Xylella fastidiosa, encoding the synthase for diffusible signal factor (DSF), was expressed in 'Freedom' grape to reduce the pathogen's growth and mobility within the plant. Symptoms in such plants were restricted to near the point of inoculation and incidence of disease was two- to fivefold lower than in the parental line. Both the longitudinal and lateral movement of X. fastidiosa in the xylem was also much lower. DSF was detected in both leaves and xylem sap of RpfF-expressing plants using biological sensors, and both 2-Z-tetradecenoic acid, previously identified as a component of X. fastidiosa DSF, and cis-11-methyl-2-dodecenoic acid were detected in xylem sap using electrospray ionization mass spectrometry. A higher proportion of X. fastidiosa cells adhered to xylem vessels of the RpfF-expressing line than parental 'Freedom' plants, reflecting a higher adhesiveness of the pathogen in the presence of DSF. Disease incidence in RpfF-expressing plants in field trials in which plants were either mechanically inoculated with X. fastidiosa or subjected to natural inoculation by sharpshooter vectors was two- to fourfold lower in than that of the parental line. The number of symptomatic leaves on infected shoots was reduced proportionally more than the incidence of infection, reflecting a decreased ability of X. fastidiosa to move within DSF-producing plants.

MODELING HOST-PATHOGEN INTERACTIONS: COMPUTATIONAL BIOLOGY AND BIOINFORMATICS FOR INFECTIOUS DISEASE RESEARCH (Session introduction)

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDermott, Jason E.; Braun, Pascal; Bonneau, Richard A.

Pathogenic infections are a major cause of both human disease and loss of crop yields and animal stocks and thus cause immense damage to the worldwide economy. The significance of infectious diseases is expected to increase in an ever more connected warming world, in which new viral, bacterial and fungal pathogens can find novel hosts and ecologic niches. At the same time, the complex and sophisticated mechanisms by which diverse pathogenic agents evade defense mechanisms and subvert their hosts networks to suit their lifestyle needs is still very incompletely understood especially from a systems perspective [1]. Thus, understanding host-pathogen interactionsmore » is both an important and a scientifically fascinating topic. Recently, technology has offered the opportunity to investigate host-pathogen interactions on a level of detail and scope that offers immense computational and analytical possibilities. Genome sequencing was pioneered on some of these pathogens, and the number of strains and variants of pathogens sequenced to date vastly outnumbers the number of host genomes available. At the same time, for both plant and human hosts more and more data on population level genomic variation becomes available and offers a rich field for analysis into the genetic interactions between host and pathogen.« less

Evolution of pathogenicity traits in the apple scab fungal pathogen in response to the domestication of its host

PubMed Central

Lê Van, Amandine; Gladieux, Pierre; Lemaire, Christophe; Cornille, Amandine; Giraud, Tatiana; Durel, Charles-Eric; Caffier, Valérie; Le Cam, Bruno

2012-01-01

Understanding how pathogens emerge is essential to bring disease-causing agents under durable human control. Here, we used cross-pathogenicity tests to investigate the changes in life-history traits of the fungal pathogen Venturia inaequalis associated with host-tracking during the domestication of apple and subsequent host-range expansion on the wild European crabapple (Malus sylvestris). Pathogenicity of 40 isolates collected in wild and domesticated ecosystems was assessed on the domesticated apple, its Central Asian main progenitor (M. sieversii) and M. sylvestris. Isolates from wild habitats in the centre of origin of the crop were not pathogenic on the domesticated apple and less aggressive than other isolates on their host of origin. Isolates from the agro-ecosystem in Central Asia infected a higher proportion of plants with higher aggressiveness, on both the domesticated host and its progenitor. Isolates from the European crabapple were still able to cause disease on other species but were less aggressive and less frequently virulent on these hosts than their endemic populations. Our results suggest that the domestication of apple was associated with the acquisition of virulence in the pathogen following host-tracking. The spread of the disease in the agro-ecosystem would also have been accompanied by an increase in overall pathogenicity. PMID:23144656

Applied genetic conservation of Hawaiian Acacia koa: an eco-regional approach

Treesearch

Nick Dudley; Tyler Jones; Robert James; Richard Sniezko; Jessica Wright; Christina Liang; Paul F. Gugger; Phil Cannon

2017-01-01

Koa (Acacia koa) is a valuable tree species economically, ecologically, and culturally in Hawaii. A vascular wilt disease of koa, caused by the fungal pathogen Fusarium oxysporum f. sp. koae (FOXY), causes high rates of mortality in field plantings and threatens native koa forests in Hawaii. Producing seeds with genetic resistance to FOXY is vital...

First report of Monilinia fructicola causing postharvest decay of strawberries (Fragaria ananassa) in the United States

USDA-ARS?s Scientific Manuscript database

Monilinia fructicola is a world-wide economically important pathogen of stone fruits causing brown rot before and after harvest. In early summer of 2016, signs of Monilinia spp. decay were observed on strawberry fruit, harvested from organically grown plants in a high tunnel located in the middle o...

Plant immunity in plant–aphid interactions

PubMed Central

Jaouannet, Maëlle; Rodriguez, Patricia A.; Lenoir, Camille J. G.; MacLeod, Ruari; Escudero-Martinez, Carmen; Bos, Jorunn I.B.

2014-01-01

Aphids are economically important pests that cause extensive feeding damage and transmit viruses. While some species have a broad host range and cause damage to a variety of crops, others are restricted to only closely related plant species. While probing and feeding aphids secrete saliva, containing effectors, into their hosts to manipulate host cell processes and promote infestation. Aphid effector discovery studies pointed out parallels between infection and infestation strategies of plant pathogens and aphids. Interestingly, resistance to some aphid species is known to involve plant resistance proteins with a typical NB-LRR domain structure. Whether these resistance proteins indeed recognize aphid effectors to trigger ETI remains to be elucidated. In addition, it was recently shown that unknown aphid derived elicitors can initiate reactive oxygen species (ROS) production and callose deposition and that these responses were dependent on BAK1 (BRASSINOSTERIOD INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE 1) which is a key component of the plant immune system. In addition, BAK-1 contributes to non-host resistance to aphids pointing to another parallel between plant-pathogen and – aphid interactions. Understanding the role of plant immunity and non-host resistance to aphids is essential to generate durable and sustainable aphid control strategies. Although insect behavior plays a role in host selection and non-host resistance, an important observation is that aphids interact with non-host plants by probing the leaf surface, but are unable to feed or establish colonization. Therefore, we hypothesize that aphids interact with non-host plants at the molecular level, but are potentially not successful in suppressing plant defenses and/or releasing nutrients. PMID:25520727

A novel Arabidopsis CHITIN ELICITOR RECEPTOR KINASE 1 (CERK1) mutant with enhanced pathogen-induced cell death and altered receptor processing.

PubMed

Petutschnig, Elena K; Stolze, Marnie; Lipka, Ulrike; Kopischke, Michaela; Horlacher, Juliane; Valerius, Oliver; Rozhon, Wilfried; Gust, Andrea A; Kemmerling, Birgit; Poppenberger, Brigitte; Braus, Gerhard H; Nürnberger, Thorsten; Lipka, Volker

2014-12-01

Plants detect pathogens by sensing microbe-associated molecular patterns (MAMPs) through pattern recognition receptors. Pattern recognition receptor complexes also have roles in cell death control, but the underlying mechanisms are poorly understood. Here, we report isolation of cerk1-4, a novel mutant allele of the Arabidopsis chitin receptor CERK1 with enhanced defense responses. We identified cerk1-4 in a forward genetic screen with barley powdery mildew and consequently characterized it by pathogen assays, mutant crosses and analysis of defense pathways. CERK1 and CERK1-4 proteins were analyzed biochemically. The cerk1-4 mutation causes an amino acid exchange in the CERK1 ectodomain. Mutant plants maintain chitin signaling capacity but exhibit hyper-inducible salicylic acid concentrations and deregulated cell death upon pathogen challenge. In contrast to chitin signaling, the cerk1-4 phenotype does not require kinase activity and is conferred by the N-terminal part of the receptor. CERK1 undergoes ectodomain shedding, a well-known process in animal cell surface proteins. Wild-type plants contain the full-length CERK1 receptor protein as well as a soluble form of the CERK1 ectodomain, whereas cerk1-4 plants lack the N-terminal shedding product. Our work suggests that CERK1 may have a chitin-independent role in cell death control and is the first report of ectodomain shedding in plants. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.

[Effect of biopesticide Pythium oligandrum broth on gummy stem blight in cucumber seedlings, animal health and plant growth].

PubMed

Geng, Mingming; Jia, Ruilian; Sui, Zongming; Huang, Jianguo

2016-07-04

Biopesticides are safe and environment friendly. We evaluated the biocontrol effect of Pythium oligandrum broth (POB) and its toxicity to animals and plant growth. Animal, antagonist, pot, and field experiments with mice, Mycosphaerella melonis, and cucumber seedlings were carried out to study animal toxicity, control of gummy stem blight, plant growth, fruit yield and quality with POB produced from self-isolated P. oligandrum CQ2010. Mouse showed normal weight, appearances, performances and no pathogenic changes in organs and tissues with a large amount of POB supplied by lavage. The inhibition rate of POB against M. melonis was 51.95%, similar to thiophanate methy (800 times dilution) but much higher than chlorothalonil (200 times dilution). Malondialdehyde concentration was reduced whereas activities of peroxidase and superoxide dismutase were stimulated in seedling leaves irrespective of POB supplied before and after pathogenic inoculation. POB also decreased the pathogenic incidence and disease index with relative control efficacy from 54.8% to 64.1%. Thus, POB could alleviate cell membrane damage caused by pathogenic microbes, stimulate physiological reactions related to disease defense, and increase disease-resistant abilities of plants. Moreover, POB increased chlorophyll content, root activity, and uptake of nitrogen, phosphorus and potassium, resulting in growth acceleration, fruit yield increment, and quality improvement. POB is safe to animals and could control gummy stem blight of cucumber seedlings, promote plant growth, increase fruit yield, and improve the qualities.

Multi-locus tree and species tree approaches toward resolving a complex clade of downy mildews (Straminipila, Oomycota), including pathogens of beet and spinach

PubMed Central

Choi, Young-Joon; Klosterman, Steven J.; Kummer, Volker; Voglmayr, Hermann; Shin, Hyeon-Dong; Thines, Marco

2017-01-01

Accurate species determination of plant pathogens is a prerequisite for their control and quarantine, and further for assessing their potential threat to crops. The family Peronosporaceae (Straminipila; Oomycota) consists of obligate biotrophic pathogens that cause downy mildew disease on angiosperms, including a large number of cultivated plants. In the largest downy mildew genus Peronospora, a phylogenetically complex clade includes the economically important downy mildew pathogens of spinach and beet, as well as the type species of the genus Peronospora. To resolve this complex clade at the species level and to infer evolutionary relationships among them, we used multi-locus phylogenetic analysis and species tree estimation. Both approaches discriminated all nine currently accepted species and revealed four previously unrecognized lineages, which are specific to a host genus or species. This is in line with a narrow species concept, i.e. that a downy mildew species is associated with only a particular host plant genus or species. Instead of applying the dubious name Peronospora farinosa, which has been proposed for formal rejection, our results provide strong evidence that Peronospora schachtii is an independent species from lineages on Atriplex and apparently occurs exclusively on Beta vulgaris. The members of the clade investigated, the Peronospora rumicis clade, associate with three different host plant families, Amaranthaceae, Caryophyllaceae, and Polygonaceae, suggesting that they may have speciated following at least two recent inter-family host shifts, rather than contemporary cospeciation with the host plants. PMID:25772799

Interaction of Phytophagous Insects with Salmonella enterica on Plants and Enhanced Persistence of the Pathogen with Macrosteles quadrilineatus Infestation or Frankliniella occidentalis Feeding

PubMed Central

Soto-Arias, José Pablo; Groves, Russell; Barak, Jeri D.

2013-01-01

Recently, most foodborne illness outbreaks of salmonellosis have been caused by consumption of contaminated fresh produce. Yet, the mechanisms that allow the human pathogen Salmonella enterica to contaminate and grow in plant environments remain poorly described. We examined the effect of feeding by phytophagous insects on survival of S. enterica on lettuce. Larger S. enterica populations were found on leaves infested with Macrosteles quadrilineatus. In contrast, pathogen populations among plants exposed to Frankliniella occidentalis or Myzus persicae were similar to those without insects. However, on plants infested with F. occidentalis, areas of the infested leaf with feeding damage sustained higher S. enterica populations than areas without damage. The spatial distribution of S. enterica cells on leaves infested with F. occidentalis may be altered resulting in higher populations in feeding lesions or survival may be different across a leaf dependent on local damage. Results suggest the possibility of some specificity with select insects and the persistence of S. enterica. Additionally, we demonstrated the potential for phytophagous insects to become contaminated with S. enterica from contaminated plant material. S. enterica was detected in approximately 50% of all M. quadrilineatus, F. occidentalis, and M. persicae after 24 h exposure to contaminated leaves. Particularly, 17% of F. occidentalis, the smallest of the insects tested, harbored more than 102 CFU/F. occidentalis. Our results show that phytophagous insects may influence the population dynamics of S. enterica in agricultural crops. This study provides evidence of a human bacterial pathogen interacting with phytophagous insect during plant infestation. PMID:24205384

Interaction of phytophagous insects with Salmonella enterica on plants and enhanced persistence of the pathogen with Macrosteles quadrilineatus infestation or Frankliniella occidentalis feeding.

PubMed

Soto-Arias, José Pablo; Groves, Russell; Barak, Jeri D

2013-01-01

Recently, most foodborne illness outbreaks of salmonellosis have been caused by consumption of contaminated fresh produce. Yet, the mechanisms that allow the human pathogen Salmonella enterica to contaminate and grow in plant environments remain poorly described. We examined the effect of feeding by phytophagous insects on survival of S. enterica on lettuce. Larger S. enterica populations were found on leaves infested with Macrosteles quadrilineatus. In contrast, pathogen populations among plants exposed to Frankliniella occidentalis or Myzus persicae were similar to those without insects. However, on plants infested with F. occidentalis, areas of the infested leaf with feeding damage sustained higher S. enterica populations than areas without damage. The spatial distribution of S. enterica cells on leaves infested with F. occidentalis may be altered resulting in higher populations in feeding lesions or survival may be different across a leaf dependent on local damage. Results suggest the possibility of some specificity with select insects and the persistence of S. enterica. Additionally, we demonstrated the potential for phytophagous insects to become contaminated with S. enterica from contaminated plant material. S. enterica was detected in approximately 50% of all M. quadrilineatus, F. occidentalis, and M. persicae after 24 h exposure to contaminated leaves. Particularly, 17% of F. occidentalis, the smallest of the insects tested, harbored more than 10(2) CFU/F. occidentalis. Our results show that phytophagous insects may influence the population dynamics of S. enterica in agricultural crops. This study provides evidence of a human bacterial pathogen interacting with phytophagous insect during plant infestation.

Activation of an AP1-Like Transcription Factor of the Maize Pathogen Cochliobolus heterostrophus in Response to Oxidative Stress and Plant Signals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lev, Sophie; hadar, Ruthi; Amedeo, Paolo

Redox sensing is a ubiquitous mechanism regulating cellular activity. Fungal pathogens face reactive oxygen species produced by the host plant's oxidative burst in addition to endogenous reactive oxygen species produced during aerobic metabolism. An array of preformed and induced detoxifying enzymes, including superoxide dismutase, catalases, and peroxidases, could allow fungi to infect plants despite the oxidative burst. We isolated a gene (CHAP1) encoding a redox-regulated transcription factor in Cochliobolus heterostrophus, a fungal pathogen of maize. CHAP1 is a bZIP protein that possesses two cysteine-rich domains structurally and functionally related to Saccharomyces cerevisiae YAP1. Deletion of CHAP1 in C. heterostrophus resultedmore » in decreased resistance to oxidative stress caused by hydrogen peroxide and menadione, but the virulence of chap1 mutants was unaffected. Upon activation by oxidizing agents or plant signals, a green fluorescent protein (GFP)-CHAP1 fusion protein became localized in the nucleus. Expression of genes encoding antioxidant proteins was induced in the wild type but not in chap1 mutants. Activation of CHAP1 occurred from the earliest stage of plant infection, in conidial germ tubes on the leaf surface, and persisted during infection. Late in the course of infection, after extensive necrotic lesions were formed, GFP-CHAP1 redistributed to the cytosol in hyphae growing on the leaf surface. Localization of CHAP1 to the nucleus may, through changes in the redox state of the cell, provide a mechanism linking extracellular cues to transcriptional regulation during the plant-pathogen interaction.« less

Defence responses regulated by jasmonate and delayed senescence caused by ethylene receptor mutation contribute to the tolerance of petunia to Botrytis cinerea.

PubMed

Wang, Hong; Liu, Gang; Li, Chunxia; Powell, Ann L T; Reid, Michael S; Zhang, Zhen; Jiang, Cai-Zhong

2013-06-01

Ethylene and jasmonate (JA) have powerful effects when plants are challenged by pathogens. The inducible promoter-regulated expression of the Arabidopsis ethylene receptor mutant ethylene-insensitive1-1 (etr1-1) causes ethylene insensitivity in petunia. To investigate the molecular mechanisms involved in transgenic petunia responses to Botrytis cinerea related to the ethylene and JA pathways, etr1-1-expressing petunia plants were inoculated with Botrytis cinerea. The induced expression of etr1-1 by a chemical inducer dexamethasone resulted in retarded senescence and reduced disease symptoms on detached leaves and flowers or intact plants. The extent of decreased disease symptoms correlated positively with etr1-1 expression. The JA pathway, independent of the ethylene pathway, activated petunia ethylene response factor (PhERF) expression and consequent defence-related gene expression. These results demonstrate that ethylene induced by biotic stress influences senescence, and that JA in combination with delayed senescence by etr1-1 expression alters tolerance to pathogens. © 2013 BSPP AND JOHN WILEY & SONS LTD.

HapX-Mediated Iron Homeostasis Is Essential for Rhizosphere Competence and Virulence of the Soilborne Pathogen Fusarium oxysporum[C][W][OA

PubMed Central

López-Berges, Manuel S.; Capilla, Javier; Turrà, David; Schafferer, Lukas; Matthijs, Sandra; Jöchl, Christoph; Cornelis, Pierre; Guarro, Josep; Haas, Hubertus; Di Pietro, Antonio

2012-01-01

Soilborne fungal pathogens cause devastating yield losses and are highly persistent and difficult to control. During the infection process, these organisms must cope with limited availability of iron. Here we show that the bZIP protein HapX functions as a key regulator of iron homeostasis and virulence in the vascular wilt fungus Fusarium oxysporum. Deletion of hapX does not affect iron uptake but causes derepression of genes involved in iron-consuming pathways, leading to impaired growth under iron-depleted conditions. F. oxysporum strains lacking HapX are reduced in their capacity to invade and kill tomato (Solanum lycopersicum) plants and immunodepressed mice. The virulence defect of ΔhapX on tomato plants is exacerbated by coinoculation of roots with a biocontrol strain of Pseudomonas putida, but not with a siderophore-deficient mutant, indicating that HapX contributes to iron competition of F. oxysporum in the tomato rhizosphere. These results establish a conserved role for HapX-mediated iron homeostasis in fungal infection of plants and mammals. PMID:22968717

Fusarium oxysporum Triggers Tissue-Specific Transcriptional Reprogramming in Arabidopsis thaliana

PubMed Central

Lyons, Rebecca; Stiller, Jiri; Powell, Jonathan; Rusu, Anca; Manners, John M.; Kazan, Kemal

2015-01-01

Some of the most devastating agricultural diseases are caused by root-infecting pathogens, yet the majority of studies on these interactions to date have focused on the host responses of aerial tissues rather than those belowground. Fusarium oxysporum is a root-infecting pathogen that causes wilt disease on several plant species including Arabidopsis thaliana. To investigate and compare transcriptional changes triggered by F. oxysporum in different Arabidopsis tissues, we infected soil-grown plants with F. oxysporum and subjected root and leaf tissue harvested at early and late timepoints to RNA-seq analyses. At least half of the genes induced or repressed by F. oxysporum showed tissue-specific regulation. Regulators of auxin and ABA signalling, mannose binding lectins and peroxidases showed strong differential expression in root tissue. We demonstrate that ARF2 and PRX33, two genes regulated in the roots, promote susceptibility to F. oxysporum. In the leaves, defensins and genes associated with the response to auxin, cold and senescence were strongly regulated while jasmonate biosynthesis and signalling genes were induced throughout the plant. PMID:25849296

Biocontrol Potential of Streptomyces hydrogenans Strain DH16 toward Alternaria brassicicola to Control Damping Off and Black Leaf Spot of Raphanus sativus

PubMed Central

Manhas, Rajesh K.; Kaur, Talwinder

2016-01-01

Biocontrol agents and their bioactive metabolites provide one of the best alternatives to decrease the use of chemical pesticides. In light of this, the present investigation reports the biocontrol potential of Streptomyces hydrogenans DH16 and its metabolites towards Alternaria brassicicola, causal agent of black leaf spot and damping off of seedlings of crucifers. In vitro antibiosis of strain against pathogen revealed complete suppression of mycelial growth of pathogen, grown in potato dextrose broth supplemented with culture supernatant (20% v/v) of S. hydrogenans DH16. Microscopic examination of the fungal growth showed severe morphological abnormalities in the mycelium caused by antifungal metabolites. In vivo studies showed the efficacy of streptomycete cells and culture supernatant as seed dressings to control damping off of Raphanus sativus seedlings. Treatment of pathogen infested seeds with culture supernatant (10%) and streptomycete cells significantly improved seed germination (75–80%) and vigor index (1167–1538). Furthermore, potential of cells and culture supernatant as foliar treatment to control black leaf spot was also evaluated. Clearly visible symptoms of disease were observed in the control plants with 66.81% disease incidence and retarded growth of root system. However, disease incidence reduced to 6.78 and 1.47% in plants treated with antagonist and its metabolites, respectively. Additionally, treatment of seeds and plants with streptomycete stimulated various growth traits of plants over uninoculated control plants in the absence of pathogen challenge. These results indicate that S. hydrogenans and its culture metabolites can be developed as biofungicides as seed dressings to control seed borne pathogens, and as sprays to control black leaf spot of crucifers. PMID:28018402

Fungal-specific transcription factor AbPf2 activates pathogenicity in Alternaria brassicicola

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, Yangrae; Ohm, Robin A.; Grigoriev, Igor V.

Alternaria brassicicola is a successful saprophyte and necrotrophic plant pathogen. To identify molecular determinants of pathogenicity, we created non-pathogenic mutants of a transcription factor-encoding gene, AbPf2. The frequency and timing of germination and appressorium formation on host plants were similar between the non-pathogenic abpf2 mutants and wild-type A. brassicicola. The mutants were also similar in vitro to wild-type A. brassicicola in terms of vegetative growth, conidium production, and responses to a phytoalexin, reactive oxygen species and osmolites. The hyphae of the mutants grew slowly but did not cause disease symptoms on the surface of host plants. Transcripts of the AbPf2more » gene increased exponentially soon after wild-type conidia contacted their host plants . A small amount of AbPf2 protein, as monitored using GFP fusions, was present in young, mature conidia. The protein level decreased during saprophytic growth, but increased and was located primarily in fungal nuclei during pathogenesis. Levels of the proteins and transcripts sharply decreased following colonization of host tissues beyond the initial infection site. When expression of the transcription factor was induced in the wild-type during early pathogenesis, 106 fungal genes were also induced in the wild-type but not in the abpf2 mutants. Notably, 33 of the 106 genes encoded secreted proteins, including eight putative effector proteins. Plants inoculated with abpf2 mutants expressed higher levels of genes associated with photosynthesis, the pentose phosphate pathway and primary metabolism, but lower levels of defense-related genes. Our results suggest that AbPf2 is an important regulator of pathogenesis, but does not affect other cellular processes in A. brassicicola.« less

Plant immunity: towards an integrated view of plant-pathogen interactions.

PubMed

Dodds, Peter N; Rathjen, John P

2010-08-01

Plants are engaged in a continuous co-evolutionary struggle for dominance with their pathogens. The outcomes of these interactions are of particular importance to human activities, as they can have dramatic effects on agricultural systems. The recent convergence of molecular studies of plant immunity and pathogen infection strategies is revealing an integrated picture of the plant-pathogen interaction from the perspective of both organisms. Plants have an amazing capacity to recognize pathogens through strategies involving both conserved and variable pathogen elicitors, and pathogens manipulate the defence response through secretion of virulence effector molecules. These insights suggest novel biotechnological approaches to crop protection.

Autophagy in plant pathogenic fungi.

PubMed

Liu, Xiao-Hong; Xu, Fei; Snyder, John Hugh; Shi, Huan-Bin; Lu, Jian-Ping; Lin, Fu-Cheng

2016-09-01

Autophagy is a conserved cellular process that degrades cytoplasmic constituents in vacuoles. Plant pathogenic fungi develop special infection structures and/or secrete a range of enzymes to invade their plant hosts. It has been demonstrated that monitoring autophagy processes can be extremely useful in visualizing the sequence of events leading to pathogenicity of plant pathogenic fungi. In this review, we introduce the molecular mechanisms involved in autophagy. In addition, we explore the relationship between autophagy and pathogenicity in plant pathogenic fungi. Finally, we discuss the various experimental strategies available for use in the study of autophagy in plant pathogenic fungi. Copyright © 2016 Elsevier Ltd. All rights reserved.

Phytophthora capsici-tomato interaction features dramatic shifts in gene expression associated with a hemi-biotrophic lifestyle.

PubMed

Jupe, Julietta; Stam, Remco; Howden, Andrew J M; Morris, Jenny A; Zhang, Runxuan; Hedley, Pete E; Huitema, Edgar

2013-06-25

Plant-microbe interactions feature complex signal interplay between pathogens and their hosts. Phytophthora species comprise a destructive group of fungus-like plant pathogens, collectively affecting a wide range of plants important to agriculture and natural ecosystems. Despite the availability of genome sequences of both hosts and microbes, little is known about the signal interplay between them during infection. In particular, accurate descriptions of coordinate relationships between host and microbe transcriptional programs are lacking. Here, we explore the molecular interaction between the hemi-biotrophic broad host range pathogen Phytophthora capsici and tomato. Infection assays and use of a composite microarray allowed us to unveil distinct changes in both P. capsici and tomato transcriptomes, associated with biotrophy and the subsequent switch to necrotrophy. These included two distinct transcriptional changes associated with early infection and the biotrophy to necrotrophy transition that may contribute to infection and completion of the P. capsici lifecycle Our results suggest dynamic but highly regulated transcriptional programming in both host and pathogen that underpin P. capsici disease and hemi-biotrophy. Dynamic expression changes of both effector-coding genes and host factors involved in immunity, suggests modulation of host immune signaling by both host and pathogen. With new unprecedented detail on transcriptional reprogramming, we can now explore the coordinate relationships that drive host-microbe interactions and the basic processes that underpin pathogen lifestyles. Deliberate alteration of lifestyle-associated transcriptional changes may allow prevention or perhaps disruption of hemi-biotrophic disease cycles and limit damage caused by epidemics.

Antifungal metabolites (monorden, monocillins I, II, III) from Colletotrichum graminicola, a systemic vascular pathogen of maize.

PubMed

Wicklow, Donald T; Jordan, Annalisa M; Gloer, James B

2009-12-01

Colletotrichum graminicola is a systemic vascular pathogen that causes anthracnose stalk rot and leaf blight of maize. In the course of an effort to explore the potential presence and roles of C. graminicola metabolites in maize, ethyl acetate extracts of solid substrate fermentations of several C. graminicola isolates from Michigan and Illinois were found to be active against Aspergillus flavus and Fusarium verticillioides, both mycotoxin-producing seed-infecting fungal pathogens. Chemical investigations of the extract of one such isolate (NRRL 47511) led to the isolation of known metabolites monorden (also known as radicicol) and monocillins I-III as major components. Monorden and monocillin I displayed in vitro activity against the stalk- and ear-rot pathogen Stenocarpella maydis while only the most abundant metabolite (monorden) showed activity against foliar pathogens Alternaria alternata, Bipolaris zeicola, and Curvularia lunata. Using LC-HRESITOFMS, monorden was detected in steam-sterilized maize stalks and stalk residues inoculated with C. graminicola but not in the necrotic stalk tissues of wound-inoculated plants grown in an environmental chamber. Monorden and monocillin I can bind and inhibit plant Hsp90, a chaperone of R-proteins. It is hypothesized that monorden and monocillins could support the C. graminicola disease cycle by disrupting maize plant defenses and by excluding other fungi from necrotic tissues and crop residues. This is the first report of natural products from C. graminicola, as well as the production of monorden and monocillins by a pathogen of cereals.

Claviceps purpurea expressing polygalacturonases escaping PGIP inhibition fully infects PvPGIP2 wheat transgenic plants but its infection is delayed in wheat transgenic plants with increased level of pectin methyl esterification.

PubMed

Volpi, Chiara; Raiola, Alessandro; Janni, Michela; Gordon, Anna; O'Sullivan, Donal M; Favaron, Francesco; D'Ovidio, Renato

2013-12-01

Claviceps purpurea is a biotrophic fungal pathogen of grasses causing the ergot disease. The infection process of C. purpurea on rye flowers is accompanied by pectin degradation and polygalacturonase (PG) activity represents a pathogenicity factor. Wheat is also infected by C. purpurea and we tested whether the presence of polygalacturonase inhibiting protein (PGIP) can affect pathogen infection and ergot disease development. Wheat transgenic plants expressing the bean PvPGIP2 did not show a clear reduction of disease symptoms when infected with C. purpurea. To ascertain the possible cause underlying this lack of improved resistance of PvPGIP2 plants, we expressed both polygalacturonases present in the C. purpurea genome, cppg1 and cppg2 in Pichia pastoris. In vitro assays using the heterologous expressed PGs and PvPGIP2 showed that neither PG is inhibited by this inhibitor. To further investigate the role of PG in the C. purpurea/wheat system, we demonstrated that the activity of both PGs of C. purpurea is reduced on highly methyl esterified pectin. Finally, we showed that this reduction in PG activity is relevant in planta, by inoculating with C. purpurea transgenic wheat plants overexpressing a pectin methyl esterase inhibitor (PMEI) and showing a high degree of pectin methyl esterification. We observed reduced disease symptoms in the transgenic line compared with null controls. Together, these results highlight the importance of pectin degradation for ergot disease development in wheat and sustain the notion that inhibition of pectin degradation may represent a possible route to control of ergot in cereals. Copyright © 2013 Elsevier Masson SAS. All rights reserved.

Potential of Pseudomonas putida PCI2 for the Protection of Tomato Plants Against Fungal Pathogens.

PubMed

Pastor, Nicolás; Masciarelli, Oscar; Fischer, Sonia; Luna, Virginia; Rovera, Marisa

2016-09-01

Tomato is one of the most economically attractive vegetable crops due to its high yields. Diseases cause significant losses in tomato production worldwide. We carried out Polymerase Chain Reaction studies to detect the presence of genes encoding antifungal compounds in the DNA of Pseudomonas putida strain PCI2. We also used liquid chromatography-electrospray tandem mass spectrometry to detect and quantify the production of compounds that increase the resistance of plants to diseases from culture supernatants of PCI2. In addition, we investigated the presence of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase in PCI2. Finally, PCI2 was used for inoculation of tomato seeds to study its potential biocontrol activity against Fusarium oxysporum MR193. The obtained results showed that no fragments for the encoding genes of hydrogen cyanide, pyoluteorin, 2,4-diacetylphloroglucinol, pyrrolnitrin, or phenazine-1-carboxylic acid were amplified from the DNA of PCI2. On the other hand, PCI2 produced salicylic acid and jasmonic acid in Luria-Bertani medium and grew in a culture medium containing ACC as the sole nitrogen source. We observed a reduction in disease incidence from 53.33 % in the pathogen control to 30 % in tomato plants pre-inoculated with PCI2 as well as increases in shoot and root dry weights in inoculated plants, as compared to the pathogenicity control. This study suggests that inoculation of tomato seeds with P. putida PCI2 increases the resistance of plants to root rot caused by F. oxysporum and that PCI2 produces compounds that may be involved at different levels in increasing such resistance. Thus, PCI2 could represent a non-contaminating management strategy potentially applicable in vegetable crops such as tomato.

Trichoderma Biocontrol: Signal Transduction Pathways Involved in Host Sensing and Mycoparasitism

PubMed Central

Zeilinger, Susanne; Omann, Markus

2007-01-01

Fungi of the genus Trichoderma are used as biocontrol agents against several plant pathogenic fungi like Rhizoctonia spp., Pythium spp., Botrytis cinerea and Fusarium spp. which cause both soil-borne and leaf- or flower-borne diseases of agricultural plants. Plant disease control by Trichoderma is based on complex interactions between Trichoderma, the plant pathogen and the plant. Until now, two main components of biocontrol have been identified: direct activity of Trichoderma against the plant pathogen by mycoparasitism and induced systemic resistance in plants. As the mycoparasitic interaction is host-specific and not merely a contact response, it is likely that signals from the host fungus are recognised by Trichoderma and provoke transcription of mycoparasitism-related genes. In the last few years examination of signalling pathways underlying Trichoderma biocontrol started and it was shown that heterotrimeric G-proteins and mitogen-activated protein (MAP) kinases affected biocontrol-relevant processes such as the production of hydrolytic enzymes and antifungal metabolites and the formation of infection structures. MAPK signalling was also found to be involved in induction of plant systemic resistance in Trichoderma virens and in the hyperosmotic stress response in Trichoderma harzianum. Analyses of the function of components of the cAMP pathway during Trichoderma biocontrol revealed that mycoparasitism-associated coiling and chitinase production as well as secondary metabolism are affected by the internal cAMP level; in addition, a cross talk between regulation of light responses and the cAMP signalling pathway was found in Trichoderma atroviride. PMID:19936091

Trichoderma biocontrol: signal transduction pathways involved in host sensing and mycoparasitism.

PubMed

Zeilinger, Susanne; Omann, Markus

2007-11-08

Fungi of the genus Trichoderma are used as biocontrol agents against several plant pathogenic fungi like Rhizoctonia spp., Pythium spp., Botrytis cinerea and Fusarium spp. which cause both soil-borne and leaf- or flower-borne diseases of agricultural plants. Plant disease control by Trichoderma is based on complex interactions between Trichoderma, the plant pathogen and the plant. Until now, two main components of biocontrol have been identified: direct activity of Trichoderma against the plant pathogen by mycoparasitism and induced systemic resistance in plants. As the mycoparasitic interaction is host-specific and not merely a contact response, it is likely that signals from the host fungus are recognised by Trichoderma and provoke transcription of mycoparasitism-related genes. In the last few years examination of signalling pathways underlying Trichoderma biocontrol started and it was shown that heterotrimeric G-proteins and mitogen-activated protein (MAP) kinases affected biocontrol-relevant processes such as the production of hydrolytic enzymes and antifungal metabolites and the formation of infection structures. MAPK signalling was also found to be involved in induction of plant systemic resistance in Trichoderma virens and in the hyperosmotic stress response in Trichoderma harzianum. Analyses of the function of components of the cAMP pathway during Trichoderma biocontrol revealed that mycoparasitism-associated coiling and chitinase production as well as secondary metabolism are affected by the internal cAMP level; in addition, a cross talk between regulation of light responses and the cAMP signalling pathway was found in Trichoderma atroviride.

The diversity of anti-microbial secondary metabolites produced by fungal endophytes: an interdisciplinary perspective.

PubMed

Mousa, Walaa Kamel; Raizada, Manish N

2013-01-01

Endophytes are microbes that inhabit host plants without causing disease and are reported to be reservoirs of metabolites that combat microbes and other pathogens. Here we review diverse classes of secondary metabolites, focusing on anti-microbial compounds, synthesized by fungal endophytes including terpenoids, alkaloids, phenylpropanoids, aliphatic compounds, polyketides, and peptides from the interdisciplinary perspectives of biochemistry, genetics, fungal biology, host plant biology, human and plant pathology. Several trends were apparent. First, host plants are often investigated for endophytes when there is prior indigenous knowledge concerning human medicinal uses (e.g., Chinese herbs). However, within their native ecosystems, and where investigated, endophytes were shown to produce compounds that target pathogens of the host plant. In a few examples, both fungal endophytes and their hosts were reported to produce the same compounds. Terpenoids and polyketides are the most purified anti-microbial secondary metabolites from endophytes, while flavonoids and lignans are rare. Examples are provided where fungal genes encoding anti-microbial compounds are clustered on chromosomes. As different genera of fungi can produce the same metabolite, genetic clustering may facilitate sharing of anti-microbial secondary metabolites between fungi. We discuss gaps in the literature and how more interdisciplinary research may lead to new opportunities to develop bio-based commercial products to combat global crop and human pathogens.

The Diversity of Anti-Microbial Secondary Metabolites Produced by Fungal Endophytes: An Interdisciplinary Perspective

PubMed Central

Mousa, Walaa Kamel; Raizada, Manish N.

2013-01-01

Endophytes are microbes that inhabit host plants without causing disease and are reported to be reservoirs of metabolites that combat microbes and other pathogens. Here we review diverse classes of secondary metabolites, focusing on anti-microbial compounds, synthesized by fungal endophytes including terpenoids, alkaloids, phenylpropanoids, aliphatic compounds, polyketides, and peptides from the interdisciplinary perspectives of biochemistry, genetics, fungal biology, host plant biology, human and plant pathology. Several trends were apparent. First, host plants are often investigated for endophytes when there is prior indigenous knowledge concerning human medicinal uses (e.g., Chinese herbs). However, within their native ecosystems, and where investigated, endophytes were shown to produce compounds that target pathogens of the host plant. In a few examples, both fungal endophytes and their hosts were reported to produce the same compounds. Terpenoids and polyketides are the most purified anti-microbial secondary metabolites from endophytes, while flavonoids and lignans are rare. Examples are provided where fungal genes encoding anti-microbial compounds are clustered on chromosomes. As different genera of fungi can produce the same metabolite, genetic clustering may facilitate sharing of anti-microbial secondary metabolites between fungi. We discuss gaps in the literature and how more interdisciplinary research may lead to new opportunities to develop bio-based commercial products to combat global crop and human pathogens. PMID:23543048

Insects as alternative hosts for phytopathogenic bacteria.

PubMed

Nadarasah, Geetanchaly; Stavrinides, John

2011-05-01

Phytopathogens have evolved specialized pathogenicity determinants that enable them to colonize their specific plant hosts and cause disease, but their intimate associations with plants also predispose them to frequent encounters with herbivorous insects, providing these phytopathogens with ample opportunity to colonize and eventually evolve alternative associations with insects. Decades of research have revealed that these associations have resulted in the formation of bacterial-vector relationships, in which the insect mediates dissemination of the plant pathogen. Emerging research, however, has highlighted the ability of plant pathogenic bacteria to use insects as alternative hosts, exploiting them as they would their primary plant host. The identification of specific bacterial genetic determinants that mediate the interaction between bacterium and insect suggests that these interactions are not incidental, but have likely arisen following the repeated association of microorganisms with particular insects over evolutionary time. This review will address the biology and ecology of phytopathogenic bacteria that interact with insects, including the traditional role of insects as vectors, as well as the newly emerging paradigm of insects serving as alternative primary hosts. Also discussed is one case where an insect serves as both host and vector, which may represent a transitionary stage in the evolution of insect-phytopathogen associations. © 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Identification and Genetic Characterization of Ralstonia solanacearum Species Complex Isolates from Cucurbita maxima in China

PubMed Central

She, Xiaoman; Yu, Lin; Lan, Guobing; Tang, Yafei; He, Zifu

2017-01-01

Ralstonia solanacearum species complex is a devastating phytopathogen with an unusually wide host range, and new host plants are continuously being discovered. In June 2016, a new bacterial wilt on Cucurbita maxima was observed in Guangdong province, China. Initially, in the adult plant stage, several leaves of each plant withered suddenly and drooped; the plant then wilted completely, and the color of their vasculature changed to dark brown, ultimately causing the entire plant to die. Creamy-whitish bacterial masses were observed to ooze from crosscut stems of these diseased plants. To develop control strategies for C. maxima bacterial wilt, the causative pathogenic isolates were identified and characterized. Twenty-four bacterial isolates were obtained from diseased C. maxima plants, and 16S rRNA gene sequencing and pathogenicity analysis results indicated that the pathogen of C. maxima bacterial wilt was Ralstonia solanacearum. The results from DNA-based analysis, host range determination and bacteriological identification confirmed that the 24 isolates belonged to R. solanacearum phylotype I, race 1, and eight of these isolates belonged to biovar 3, while 16 belonged to biovar 4. Based on the results of partial egl gene sequence analysis, the 24 isolates clustered into three egl- sequence type groups, sequevars 17, 45, and 56. Sequevar 56 is a new sequevar which is described for the first time in this paper. An assessment of the resistance of 21 pumpkin cultivars revealed that C. moschata cv. Xiangyu1 is resistant to strain RS378, C. moschata cv. Xiangmi is moderately resistant to strain RS378, and 19 other pumpkin cultivars, including four C. maxima cultivars and 15 C. moschata cultivars, are susceptible to strain RS378. To the best of our knowledge, this is the first report of C. maxima bacterial wilt caused by R. solanacearum race 1 in the world. Our results provide valuable information for the further development of control strategies for C. maxima wilt disease. PMID:29093727

Identification and Genetic Characterization of Ralstonia solanacearum Species Complex Isolates from Cucurbita maxima in China.

PubMed

She, Xiaoman; Yu, Lin; Lan, Guobing; Tang, Yafei; He, Zifu

2017-01-01

Ralstonia solanacearum species complex is a devastating phytopathogen with an unusually wide host range, and new host plants are continuously being discovered. In June 2016, a new bacterial wilt on Cucurbita maxima was observed in Guangdong province, China. Initially, in the adult plant stage, several leaves of each plant withered suddenly and drooped; the plant then wilted completely, and the color of their vasculature changed to dark brown, ultimately causing the entire plant to die. Creamy-whitish bacterial masses were observed to ooze from crosscut stems of these diseased plants. To develop control strategies for C. maxima bacterial wilt, the causative pathogenic isolates were identified and characterized. Twenty-four bacterial isolates were obtained from diseased C. maxima plants, and 16S rRNA gene sequencing and pathogenicity analysis results indicated that the pathogen of C. maxima bacterial wilt was Ralstonia solanacearum . The results from DNA-based analysis, host range determination and bacteriological identification confirmed that the 24 isolates belonged to R. solanacearum phylotype I, race 1, and eight of these isolates belonged to biovar 3, while 16 belonged to biovar 4. Based on the results of partial egl gene sequence analysis, the 24 isolates clustered into three egl- sequence type groups, sequevars 17, 45, and 56. Sequevar 56 is a new sequevar which is described for the first time in this paper. An assessment of the resistance of 21 pumpkin cultivars revealed that C. moschata cv. Xiangyu1 is resistant to strain RS378, C. moschata cv. Xiangmi is moderately resistant to strain RS378, and 19 other pumpkin cultivars, including four C. maxima cultivars and 15 C. moschata cultivars, are susceptible to strain RS378. To the best of our knowledge, this is the first report of C. maxima bacterial wilt caused by R. solanacearum race 1 in the world. Our results provide valuable information for the further development of control strategies for C. maxima wilt disease.

Genomics-Based Exploration of Virulence Determinants and Host-Specific Adaptations of Pseudomonas syringae Strains Isolated from Grasses

PubMed Central

Dudnik, Alexey; Dudler, Robert

2014-01-01

The Pseudomonas syringae species complex has recently been named the number one plant pathogen, due to its economic and environmental impacts, as well as for its role in scientific research. The bacterium has been repeatedly reported to cause outbreaks on bean, cucumber, stone fruit, kiwi and olive tree, as well as on other crop and non-crop plants. It also serves as a model organism for research on the Type III secretion system (T3SS) and plant-pathogen interactions. While most of the current work on this pathogen is either carried out on one of three model strains found on dicot plants with completely sequenced genomes or on isolates obtained from recent outbreaks, not much is known about strains isolated from grasses (Poaceae). Here, we use comparative genomics in order to identify putative virulence-associated genes and other Poaceae-specific adaptations in several newly available genome sequences of strains isolated from grass species. All strains possess only a small number of known Type III effectors, therefore pointing to the importance of non-Type III secreted virulence factors. The implications of this finding are discussed. PMID:25437611

Contribution of proteomics to the study of plant pathogenic fungi.

PubMed

Gonzalez-Fernandez, Raquel; Jorrin-Novo, Jesus V

2012-01-01

Phytopathogenic fungi are one of the most damaging plant parasitic organisms, and can cause serious diseases and important yield losses in crops. The study of the biology of these microorganisms and the interaction with their hosts has experienced great advances in recent years due to the development of moderm, holistic and high-throughput -omic techniques, together with the increasing number of genome sequencing projects and the development of mutants and reverse genetics tools. We highlight among these -omic techniques the importance of proteomics, which has become a relevant tool in plant-fungus pathosystem research. Proteomics intends to identify gene products with a key role in pathogenicity and virulence. These studies would help in the search of key protein targets and in the development of agrochemicals, which may open new ways for crop disease diagnosis and protection. In this review, we made an overview on the contribution of proteomics to the knowledge of life cycle, infection mechanisms, and virulence of the plant pathogenic fungi. Data from current, innovative literature, according to both methodological and experimental systems, were summarized and discussed. Specific sections were devoted to the most studied fungal phytopathogens: Botrytis cinerea, Sclerotinia sclerotiorum, and Fusarium graminearum.

Inducible defense against pathogens and parasites: optimal choice among multiple options.

PubMed

Shudo, E; Iwasa, Y

2001-03-21

Defense against pathogen, parasites and herbivores is often enhanced after their invasion into the host's body. Sometimes different options are adopted depending on the identity and the quantity of the pathogen, exemplified by the switch between Th1 and Th2 systems in mammalian immunity. In this paper, we study the optimal defense of the host when two alternative responses are available, which differ in the effectiveness of suppressing the growth of pathogen (parasite, or herbivore), the damage to the host caused by the defense response, and the magnitude of time delay before the defense response becomes fully effective. The optimal defense is the one that minimizes the sum of the damages caused by the pathogen and the cost due to defense activities. The damage by pathogens increases in proportion to the time integral of the pathogen abundance, and the cost is proportional to the defense activity. We can prove that a single globally optimal combination of defense options always exists and there is no other local optimum. Depending on the parameters, the optimal is to adopt only the early response, only the late response, or both responses. The defense response with a shorter time delay is more heavily used when the pathogen grows fast, the initial pathogen abundance is large, and the difference in time delay is long. We also study the host's optimal choice between constitutive and inducible defenses. In the constitutive defense, the response to pathogen attack works without delay, but it causes the cost even when the pathogen attack does not occur. We discuss mammalian immunity and the plant chemical defense from the model's viewpoint. Copyright 2001 Academic Press.

List of New Names of Plant Pathogenic Bacteria (2008-2010)

USDA-ARS?s Scientific Manuscript database

In 2010 the International Society of Plant Pathology Committee on the Taxonomy of Plant Pathogenic Bacteria published the Comprehensive List of Names of Plant Pathogenic Bacteria, 1980-2007 to provide an authoritative register of names of plant pathogens. In this manuscript we up-date the list of na...

Evolution, Diversity, and Taxonomy of the Peronosporaceae, with Focus on the Genus Peronospora.

PubMed

Thines, Marco; Choi, Young-Joon

2016-01-01

Downy mildews are a notorious group of oomycete plant pathogens, causing high economic losses in various crops and ornamentals. The most species-rich genus of oomycetes is the genus Peronospora. This review provides a wide overview of these pathogens, ranging from macro- and micro-evolutionary patterns, their biodiversity and ecology to short overviews for the currently economically most important pathogens and potential emerging diseases. In this overview, the taxonomy of economically relevant species is also discussed, as the application of the correct names and species concepts is a prerequisite for effective quarantine regulations and phytosanitary measures.

Two pathogenic species of Pythium: P. aphanidermatum and P. diclinum from a wheat field.

PubMed

Al-Sheikh, Hashem

2010-10-01

During a survey of pathogenic and non-pathogenic Pythium spp. in different localities in Egypt, several isolates of Pythia were obtained and maintained on corn meal agar. Among these isolates, Pythium aphanidermatum and Pythium diclinum were obtained from rhizosphere of wheat plants grown in Dear Attia village, Minia, Egypt. Identification was made using morphological and molecular analyses. P. aphanidermatum and P. diclinum were able to cause reductions in emergence and adulating in wheat in laboratory scale. P. aphanidermatum appeared to be the most aggressive parasite under agar and pot experimental conditions.

Two pathogenic species of Pythium: P. aphanidermatum and P. diclinum from a wheat field

PubMed Central

Al-Sheikh, Hashem

2010-01-01

During a survey of pathogenic and non-pathogenic Pythium spp. in different localities in Egypt, several isolates of Pythia were obtained and maintained on corn meal agar. Among these isolates, Pythium aphanidermatum and Pythium diclinum were obtained from rhizosphere of wheat plants grown in Dear Attia village, Minia, Egypt. Identification was made using morphological and molecular analyses. P. aphanidermatum and P. diclinum were able to cause reductions in emergence and adulating in wheat in laboratory scale. P. aphanidermatum appeared to be the most aggressive parasite under agar and pot experimental conditions. PMID:23961096

Medfly Ceratitis capitata as Potential Vector for Fire Blight Pathogen Erwinia amylovora: Survival and Transmission.

PubMed

Ordax, Mónica; Piquer-Salcedo, Jaime E; Santander, Ricardo D; Sabater-Muñoz, Beatriz; Biosca, Elena G; López, María M; Marco-Noales, Ester

2015-01-01

Monitoring the ability of bacterial plant pathogens to survive in insects is required for elucidating unknown aspects of their epidemiology and for designing appropriate control strategies. Erwinia amylovora is a plant pathogenic bacterium that causes fire blight, a devastating disease in apple and pear commercial orchards. Studies on fire blight spread by insects have mainly focused on pollinating agents, such as honeybees. However, the Mediterranean fruit fly (medfly) Ceratitis capitata (Diptera: Tephritidae), one of the most damaging fruit pests worldwide, is also common in pome fruit orchards. The main objective of the study was to investigate whether E. amylovora can survive and be transmitted by the medfly. Our experimental results show: i) E. amylovora can survive for at least 8 days inside the digestive tract of the medfly and until 28 days on its external surface, and ii) medflies are able to transmit the bacteria from inoculated apples to both detached shoots and pear plants, being the pathogen recovered from lesions in both cases. This is the first report on E. amylovora internalization and survival in/on C. capitata, as well as the experimental transmission of the fire blight pathogen by this insect. Our results suggest that medfly can act as a potential vector for E. amylovora, and expand our knowledge on the possible role of these and other insects in its life cycle.

Medfly Ceratitis capitata as Potential Vector for Fire Blight Pathogen Erwinia amylovora: Survival and Transmission

PubMed Central

Ordax, Mónica; Piquer-Salcedo, Jaime E.; Santander, Ricardo D.; Sabater-Muñoz, Beatriz; Biosca, Elena G.; López, María M.; Marco-Noales, Ester

2015-01-01

Monitoring the ability of bacterial plant pathogens to survive in insects is required for elucidating unknown aspects of their epidemiology and for designing appropriate control strategies. Erwinia amylovora is a plant pathogenic bacterium that causes fire blight, a devastating disease in apple and pear commercial orchards. Studies on fire blight spread by insects have mainly focused on pollinating agents, such as honeybees. However, the Mediterranean fruit fly (medfly) Ceratitis capitata (Diptera: Tephritidae), one of the most damaging fruit pests worldwide, is also common in pome fruit orchards. The main objective of the study was to investigate whether E. amylovora can survive and be transmitted by the medfly. Our experimental results show: i) E. amylovora can survive for at least 8 days inside the digestive tract of the medfly and until 28 days on its external surface, and ii) medflies are able to transmit the bacteria from inoculated apples to both detached shoots and pear plants, being the pathogen recovered from lesions in both cases. This is the first report on E. amylovora internalization and survival in/on C. capitata, as well as the experimental transmission of the fire blight pathogen by this insect. Our results suggest that medfly can act as a potential vector for E. amylovora, and expand our knowledge on the possible role of these and other insects in its life cycle. PMID:25978369

FvSNF1, the sucrose non-fermenting protein kinase gene of Fusarium virguliforme, is required for cell-wall-degrading enzymes expression and sudden death syndrome development in soybean.

PubMed

Islam, Kazi T; Bond, Jason P; Fakhoury, Ahmad M

2017-08-01

Fusarium virguliforme is a soil-borne pathogenic fungus that causes sudden death syndrome (SDS) in soybean. Its pathogenicity is believed to require the activity of cell-wall-degrading enzymes (CWDEs). The sucrose non-fermenting protein kinase 1 gene (SNF1) is a key component of the glucose de-repression pathway in yeast, and a regulator of gene expression for CWDEs in some plant pathogenic fungi. To elucidate the functional role of the SNF1 homolog in F. virguliforme, FvSNF1 was disrupted using a split-marker strategy. Disruption of FvSNF1 in F. virguliforme abolishes galactose utilization and causes poor growth on xylose, arabinose and sucrose. However, the resulting Fvsnf1 mutant grew similar to wild-type and ectopic transformants on glucose, fructose, maltose, or pectin as the main source of carbon. The Fvsnf1 mutant displayed no expression of the gene-encoding galactose oxidase (GAO), a secretory enzyme that catalyzes oxidation of D-galactose. It also exhibited a significant reduction in the expression of several CWDE-coding genes in contrast to the wild-type strain. Greenhouse pathogenicity assays revealed that the Fvsnf1 mutant was severely impaired in its ability to cause SDS on challenged soybean plants. Microscopy and microtome studies on infected roots showed that the Fvsnf1 mutant was defective in colonizing vascular tissue of infected plants. Cross and longitudinal sections of infected roots stained with fluorescein-labeled wheat germ agglutinin and Congo red showed that the Fvsnf1 mutant failed to colonize the xylem vessels and phloem tissue at later stages of infection. Quantification of the fungal biomass in inoculated roots further confirmed a reduced colonization of roots by the Fvsnf1 mutant when compared to the wild type. These findings suggest that FvSNF1 regulates the expression of CWDEs in F. virguliforme, thus affecting the virulence of the fungus on soybean.

The Pathogen-Host Interactions database (PHI-base): additions and future developments.

PubMed

Urban, Martin; Pant, Rashmi; Raghunath, Arathi; Irvine, Alistair G; Pedro, Helder; Hammond-Kosack, Kim E

2015-01-01

Rapidly evolving pathogens cause a diverse array of diseases and epidemics that threaten crop yield, food security as well as human, animal and ecosystem health. To combat infection greater comparative knowledge is required on the pathogenic process in multiple species. The Pathogen-Host Interactions database (PHI-base) catalogues experimentally verified pathogenicity, virulence and effector genes from bacterial, fungal and protist pathogens. Mutant phenotypes are associated with gene information. The included pathogens infect a wide range of hosts including humans, animals, plants, insects, fish and other fungi. The current version, PHI-base 3.6, available at http://www.phi-base.org, stores information on 2875 genes, 4102 interactions, 110 host species, 160 pathogenic species (103 plant, 3 fungal and 54 animal infecting species) and 181 diseases drawn from 1243 references. Phenotypic and gene function information has been obtained by manual curation of the peer-reviewed literature. A controlled vocabulary consisting of nine high-level phenotype terms permits comparisons and data analysis across the taxonomic space. PHI-base phenotypes were mapped via their associated gene information to reference genomes available in Ensembl Genomes. Virulence genes and hotspots can be visualized directly in genome browsers. Future plans for PHI-base include development of tools facilitating community-led curation and inclusion of the corresponding host target(s). © The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.

High cytokinin levels induce a hypersensitive-like response in tobacco.

PubMed

Novák, Jan; Pavlů, Jaroslav; Novák, Ondřej; Nožková-Hlaváčková, Vladimíra; Špundová, Martina; Hlavinka, Jan; Koukalová, Šárka; Skalák, Jan; Černý, Martin; Brzobohatý, Břetislav

2013-07-01

Cytokinins are positive regulators of shoot development. However, it has previously been demonstrated that efficient activation of the cytokinin biosynthesis gene ipt can cause necrotic lesions and wilting in tobacco leaves. Some plant pathogens reportedly use their ability to produce cytokinins in disease development. In response to pathogen attacks, plants can trigger a hypersensitive response that rapidly kills cells near the infection site, depriving the pathogen of nutrients and preventing its spread. In this study, a diverse set of processes that link ipt activation to necrotic lesion formation were investigated in order to evaluate the potential of cytokinins as signals and/or mediators in plant defence against pathogens. The binary pOp-ipt/LhGR system for dexamethasone-inducible ipt expression was used to increase endogenous cytokinin levels in transgenic tobacco. Changes in the levels of cytokinins and the stress hormones salicylic, jasmonic and abscisic acid following ipt activation were determined by ultra-performance liquid chromatography-electrospray tandem mass spectrometry (UPLC-MS/MS). Trends in hydrogen peroxide content and lipid peroxidation were monitored using the potassium iodide and malondialdehyde assays. The subcellular distribution of hydrogen peroxide was investigated using 3,3'-diaminobenzidine staining. The dynamics of transcripts related to photosynthesis and pathogen response were analysed by reverse transcription followed by quantitative PCR. The effects of cytokinins on photosynthesis were deciphered by analysing changes in chlorophyll fluorescence and leaf gas exchange. Plants can produce sufficiently high levels of cytokinins to trigger fast cell death without any intervening chlorosis - a hallmark of the hypersensitive response. The results suggest that chloroplastic hydrogen peroxide orchestrates the molecular responses underpinning the hypersensitive-like response, including the inhibition of photosynthesis, elevated levels of stress hormones, oxidative membrane damage and stomatal closure. Necrotic lesion formation triggered by ipt activation closely resembles the hypersensitive response. Cytokinins may thus act as signals and/or mediators in plant defence against pathogen attack.

A novel pathogenicity gene is required in the rice blast fungus to suppress the basal defenses of the host.

PubMed

Chi, Myoung-Hwan; Park, Sook-Young; Kim, Soonok; Lee, Yong-Hwan

2009-04-01

For successful colonization and further reproduction in host plants, pathogens need to overcome the innate defenses of the plant. We demonstrate that a novel pathogenicity gene, DES1, in Magnaporthe oryzae regulates counter-defenses against host basal resistance. The DES1 gene was identified by screening for pathogenicity-defective mutants in a T-DNA insertional mutant library. Bioinformatic analysis revealed that this gene encodes a serine-rich protein that has unknown biochemical properties, and its homologs are strictly conserved in filamentous Ascomycetes. Targeted gene deletion of DES1 had no apparent effect on developmental morphogenesis, including vegetative growth, conidial germination, appressorium formation, and appressorium-mediated penetration. Conidial size of the mutant became smaller than that of the wild type, but the mutant displayed no defects on cell wall integrity. The Deltades1 mutant was hypersensitive to exogenous oxidative stress and the activity and transcription level of extracellular enzymes including peroxidases and laccases were severely decreased in the mutant. In addition, ferrous ion leakage was observed in the Deltades1 mutant. In the interaction with a susceptible rice cultivar, rice cells inoculated with the Deltades1 mutant exhibited strong defense responses accompanied by brown granules in primary infected cells, the accumulation of reactive oxygen species (ROS), the generation of autofluorescent materials, and PR gene induction in neighboring tissues. The Deltades1 mutant displayed a significant reduction in infectious hyphal extension, which caused a decrease in pathogenicity. Notably, the suppression of ROS generation by treatment with diphenyleneiodonium (DPI), an inhibitor of NADPH oxidases, resulted in a significant reduction in the defense responses in plant tissues challenged with the Deltades1 mutant. Furthermore, the Deltades1 mutant recovered its normal infectious growth in DPI-treated plant tissues. These results suggest that DES1 functions as a novel pathogenicity gene that regulates the activity of fungal proteins, compromising ROS-mediated plant defense.

Ecology, Epidemiology and Disease Management of Ralstonia syzygii in Indonesia

PubMed Central

Safni, Irda; Subandiyah, Siti; Fegan, Mark

2018-01-01

Ralstonia solanacearum species complex phylotype IV strains, which have been primarily isolated from Indonesia, Australia, Japan, Korea, and Malaysia, have undergone recent taxonomic and nomenclatural changes to be placed in the species Ralstonia syzygii. This species contains three subspecies; Ralstonia syzygii subsp. syzygii, a pathogen causing Sumatra disease of clove trees in Indonesia, Ralstonia syzygii subsp. indonesiensis, the causal pathogen of bacterial wilt disease on a wide range of host plants, and Ralstonia syzygii subsp. celebesensis, the causal pathogen of blood disease on Musa spp. In Indonesia, these three subspecies have devastated the cultivation of susceptible host plants which have high economic value. Limited knowledge on the ecology and epidemiology of the diseases has hindered the development of effective control strategies. In this review, we provide insights into the ecology, epidemiology and disease control of these three subspecies of Ralstonia syzygii. PMID:29662468

Expression of pathogenicity-related genes of Xylella fastidiosa in vitro and in planta.

PubMed

de Souza, Alessandra A; Takita, Marco A; Pereira, Eridan O; Coletta-Filho, Helvécio D; Machado, Marcos A

2005-04-01

Xylella fastidiosa is responsible for several economically important plant diseases. It is currently assumed that the symptoms are caused by vascular occlusion due to biofilm formation. Microarray technology was previously used to examine the global gene expression profile of X. fastidiosa freshly isolated from symptomatic plants or after several passages by axenic culture medium, and different pathogenicity profiles have been obtained. In the present study the expression of some pathogenicity-related genes was evaluated in vitro and in planta by RT-PCR. The results suggest that adhesion is important at the beginning of biofilm formation, while the genes related to adaptation are essential for the organism's maintenance in planta. Similar results were observed in vitro mainly for the adhesion genes. The pattern of expression observed suggests that adhesion modulates biofilm formation whereas the expression of some adaptation genes may be related to the environment in which the organism is living.

An aversion to Verticillium

USDA-ARS?s Scientific Manuscript database

Verticillium wilt is a one of the most serious diseases affecting field production of ornamental trees and shrubs. The disease is caused by the soilborne fungus, Verticillium dahliae. The pathogen is very common in agricultural fields and infects hundreds of economically important plant species incl...

A faster infection assay for Armillaria using Herbaceous plants

USDA-ARS?s Scientific Manuscript database

Armillaria (honey fungus) is a virulent necrotrophic pathogen that causes Armillaria root disease. Conventional Armillaria inoculation assays use young saplings as hosts and consequently are cumbersome, frequently conducted outdoors and take many years from establishment to analysis of infection. We...

Machine learning for characterization of insect vector feeding

USDA-ARS?s Scientific Manuscript database

Insects that feed by ingesting plant and animal fluids cause devastating damage to humans, livestock, and agriculture worldwide, primarily by transmitting phytopathogenic and zoonotic pathogens. The feeding processes required for successful disease transmission by sucking insects can be recorded by ...

Comparative Genome Analysis Reveals Adaptation to the Ectophytic Lifestyle of Sooty Blotch and Flyspeck Fungi.

PubMed

Xu, Chao; Zhang, Rong; Sun, Guangyu; Gleason, Mark L

2017-11-01

Sooty blotch and flyspeck (SBFS) fungi are a distinctive group of plant pathogens which, although phylogenetically diverse, occupy an exclusively surface-dwelling niche. They cause economic losses by superficially blemishing the fruit of several tree crops, principally apple, in moist temperate regions worldwide. In this study, we performed genome-wide comparative analyses separately within three pairs of species of ascomycete pathogens; each pair contained an SBFS species as well as a closely related but plant-penetrating parasite (PPP) species. Our results showed that all three of the SBFS pathogens had significantly smaller genome sizes, gene numbers and repeat ratios than their counterpart PPPs. The pathogenicity-related genes encoding MFS transporters, secreted proteins (mainly effectors and peptidases), plant cell wall degrading enzymes, and secondary metabolism enzymes were also drastically reduced in the SBFS fungi compared with their PPP relatives. We hypothesize that the above differences in genome composition are due largely to different levels of acquisition, loss, expansion, and contraction of gene families and emergence of orphan genes. Furthermore, results suggested that horizontal gene transfer may have played a role, although limited, in the divergent evolutionary paths of SBFS pathogens and PPPs; repeat-induced point mutation could have inhibited the propagation of transposable elements and expansion of gene families in the SBFS group, given that this mechanism is stronger in the SBFS fungi than in their PPP relatives. These results substantially broaden understanding of evolutionary mechanisms of adaptation of fungi to the epicuticular niche of plants. © The Author 2017. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

QTL mapping of multiple independent loci for resistance to fusarium wilt races 1 and 4 in an interspecific cotton population

USDA-ARS?s Scientific Manuscript database

Fusarium wilt, caused by the soil-borne fungal pathogen Fusarium oxysporum f. sp. vasinfectum (FOV), is a vascular disease of cotton (Gossypium spp.). FOV race 1 (FOV1) causes major plant injury and yield loss in G. hirsutum cultivars with co-infection with root-knot nematode (Meloidogyne incognita)...

Evaluation of soybean breeding lines for resistance to Phomopsis seed decay: Results of 2014, 2015, and 2016 field trials in Stoneville, Mississippi

USDA-ARS?s Scientific Manuscript database

Soybean [Glycine max (L.) Merr.] is one of the most important crops in the world. Phomopsis seed decay (PSD) is a soybean seed disease that causes poor seed quality. This disease is caused primarily by a fungal pathogen, Phomopsis longicolla (syn. Diaporthe longicolla). Planting PSD-resistant soybea...

Potassium fertilizer applied immediately after planting had no impact on Douglas-fir seedling mortality caused by laminated root rot on a forested site in Washington State.

Treesearch

Walter G. Thies; Rick G. Kelsey; Douglas J. Westlind; Jeff Madsen

2006-01-01

Phellinus weirii causes laminated root rot (LRR), a major disease affecting growth and survival of Pseudotsuga menziesii (Douglas-fir) and other commercially important conifer species throughout the Pacific Northwest. Increasing tree vigor and resistance to pathogens through application of K fertilizer is a suggested disease...

One Health and Food-Borne Disease: Salmonella Transmission between Humans, Animals, and Plants.

PubMed

Silva, Claudia; Calva, Edmundo; Maloy, Stanley

2014-02-01

There are >2,600 recognized serovars of Salmonella enterica. Many of these Salmonella serovars have a broad host range and can infect a wide variety of animals, including mammals, birds, reptiles, amphibians, fish, and insects. In addition, Salmonella can grow in plants and can survive in protozoa, soil, and water. Hence, broad-host-range Salmonella can be transmitted via feces from wild animals, farm animals, and pets or by consumption of a wide variety of common foods: poultry, beef, pork, eggs, milk, fruit, vegetables, spices, and nuts. Broad-host-range Salmonella pathogens typically cause gastroenteritis in humans. Some Salmonella serovars have a more restricted host range that is associated with changes in the virulence plasmid pSV, accumulation of pseudogenes, and chromosome rearrangements. These changes in host-restricted Salmonella alter pathogen-host interactions such that host-restricted Salmonella organisms commonly cause systemic infections and are transmitted between host populations by asymptomatic carriers. The secondary consequences of efforts to eliminate host-restricted Salmonella serovars demonstrate that basic ecological principles govern the environmental niches occupied by these pathogens, making it impossible to thwart Salmonella infections without a clear understanding of the human, animal, and environmental reservoirs of these pathogens. Thus, transmission of S. enterica provides a compelling example of the One Health paradigm because reducing human infections will require the reduction of Salmonella in animals and limitation of transmission from the environment.

How glyphosate affects plant disease development: it is more than enhanced susceptibility.

PubMed

Hammerschmidt, Ray

2018-05-01

Glyphosate has been shown to affect the development of plant disease in several ways. Plants utilize phenolic and other shikimic acid pathway-derived compounds as part of their defense against pathogens, and glyphosate inhibits the biosynthesis of these compounds via its mode of action. Several studies have shown a correlation between enhanced disease and suppression of phenolic compound production after glyphosate. Glyphosate-resistant crop plants have also been studied for changes in resistance as a result of carrying the glyphosate resistance trait. The evidence indicates that neither the resistance trait nor application of glyphosate to glyphosate-resistant plants increases susceptibility to disease. The only exceptions to this are cases where glyphosate has been shown to reduce rust diseases on glyphosate-resistant crops, supporting a fungicidal role for this chemical. Finally, glyphosate treatment of weeds or volunteer crops can cause a temporary increase in soil-borne pathogens that may result in disease development if crops are planted too soon after glyphosate application. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

Antifungal activity of medicinal plant extracts; preliminary screening studies.

PubMed

Webster, Duncan; Taschereau, Pierre; Belland, René J; Sand, Crystal; Rennie, Robert P

2008-01-04

In the setting of HIV and organ transplantation, opportunistic fungal infections have become a common cause of morbidity and mortality. Thus antifungal therapy is playing a greater role in health care. Traditional plants are a valuable source of novel antifungals. To assess in vitro antifungal activity of aqueous plant extracts. The minimum inhibitory concentrations were determined for each extract in the setting of human pathogenic fungal isolates. Plants were harvested and identification verified. Aqueous extracts were obtained and antifungal susceptibilities determined using serial dilutional extracts with a standardized microdilution broth methodology. Twenty-three fungal isolates were cultured and exposed to the plant extracts. Five known antifungals were used as positive controls. Results were read at 48 and 72 h. Of the 14 plants analyzed, Fragaria virginiana Duchesne, Epilobium angustifolium L. and Potentilla simplex Michx. demonstrated strong antifungal potential overall. Fragaria virginiana had some degree of activity against all of the fungal pathogens. Alnus viridis DC., Betula alleghaniensis Britt. and Solidago gigantea Ait. also demonstrated a significant degree of activity against many of the yeast isolates. Fragaria virginiana, Epilobium angustifolium and Potentilla simplex demonstrate promising antifungal potential.

Transcriptional analysis of sweet orange trees co-infected with 'Candidatus Liberibacter asiaticus' and mild or severe strains of Citrus tristeza virus.

PubMed

Fu, Shimin; Shao, Jonathan; Paul, Cristina; Zhou, Changyong; Hartung, John S

2017-10-31

Citrus worldwide is threatened by huanglongbing (HLB) and tristeza diseases caused by 'Candidatus Liberibacter asiaticus' (CaLas) and Citrus tristeza virus (CTV). Although the pathogens are members of the α-proteobacteria and Closteroviridae, respectively, both are restricted to phloem cells in infected citrus and are transmitted by insect vectors. The response of sweet orange to single infection by either of these two pathogens has been characterized previously by global gene expression analysis. But because of the ubiquity of these pathogens where the diseases occur, co-infection by both pathogens is very common and could lead to increased disease severity based on synergism. We therefore co-inoculated sweet orange trees with CaLas and either a mild or a severe strain of CTV, and measured changes of gene expression in host plants. In plants infected with CaLas-B232, the overall alteration in gene expression was much greater in plants co-inoculated with the severe strain of CTV, B6, than when co-infected with the mild strain of CTV, B2. Plants co-infected with CaLas-B232 and either strain of CTV died but trees co-infected with CTV-B2 survived much longer than those co-infected with CTV-B6. Many important pathways were perturbed by both CTV-B2/CaLas-B232 and/or CTV-B6/CaLas-B232, but always more severely by CTV-B6/CaLas-B232. Genes related to cell wall modification and metal transport responded differently to infection by the pathogens in combination than by the same pathogens singly. The expressions of genes encoding phloem proteins and sucrose loading proteins were also differentially altered in response to CTV-B2 or CTV-B6 in combination with CaLas-B232, leading to different phloem environments in plants co-infected by CaLas and mild or severe CTV. Many host genes were expressed differently in response to dual infection as compared to single infections with the same pathogens. Interactions of the pathogens within the host may lead to a better or worse result for the host plant. CTV-B6 may exert a synergistic effect with CaLas-B232 in weakening the plant; on the other hand, the responses activated by the mild strain CTV-B2 may provide some beneficial effects against CaLas-B232 by increasing the defense response of the host.

Tracking cashew economically important diseases in the West African region using metagenomics

PubMed Central

Monteiro, Filipa; Romeiras, Maria M.; Figueiredo, Andreia; Sebastiana, Mónica; Baldé, Aladje; Catarino, Luís; Batista, Dora

2015-01-01

During the last decades, agricultural land-uses in West Africa were marked by dramatic shifts in the coverage of individual crops. Nowadays, cashew (Anacardium occidentale L.) is one of the most export-oriented horticulture crops, notably in Guinea-Bissau. Relying heavily on agriculture to increase their income, developing countries have been following a strong trend of moving on from traditional farming systems toward commercial production. Emerging infectious diseases, driven either by adaptation to local conditions or inadvertent importation of plant pathogens, are able to cause tremendous cashew production losses, with economic and social impact of which, in developing countries is often underestimated. Presently, plant genomics with metagenomics as an emergent tool, presents an enormous potential to better characterize diseases by providing extensive knowledge on plant pathogens at a large scale. In this perspective, we address metagenomics as a promising genomic tool to identify cashew fungal associated diseases as well as to discriminate the causal pathogens, aiming at obtaining tools to help design effective strategies for disease control and thus promote the sustainable production of cashew in West African Region. PMID:26175748

Tracking cashew economically important diseases in the West African region using metagenomics.

PubMed

Monteiro, Filipa; Romeiras, Maria M; Figueiredo, Andreia; Sebastiana, Mónica; Baldé, Aladje; Catarino, Luís; Batista, Dora

2015-01-01

During the last decades, agricultural land-uses in West Africa were marked by dramatic shifts in the coverage of individual crops. Nowadays, cashew (Anacardium occidentale L.) is one of the most export-oriented horticulture crops, notably in Guinea-Bissau. Relying heavily on agriculture to increase their income, developing countries have been following a strong trend of moving on from traditional farming systems toward commercial production. Emerging infectious diseases, driven either by adaptation to local conditions or inadvertent importation of plant pathogens, are able to cause tremendous cashew production losses, with economic and social impact of which, in developing countries is often underestimated. Presently, plant genomics with metagenomics as an emergent tool, presents an enormous potential to better characterize diseases by providing extensive knowledge on plant pathogens at a large scale. In this perspective, we address metagenomics as a promising genomic tool to identify cashew fungal associated diseases as well as to discriminate the causal pathogens, aiming at obtaining tools to help design effective strategies for disease control and thus promote the sustainable production of cashew in West African Region.

The Colletotrichum destructivum species complex – hemibiotrophic pathogens of forage and field crops

PubMed Central

Damm, U.; O'Connell, R.J.; Groenewald, J.Z.; Crous, P.W.

2014-01-01

Colletotrichum destructivum is an important plant pathogen, mainly of forage and grain legumes including clover, alfalfa, cowpea and lentil, but has also been reported as an anthracnose pathogen of many other plants worldwide. Several Colletotrichum isolates, previously reported as closely related to C. destructivum, are known to establish hemibiotrophic infections in different hosts. The inconsistent application of names to those isolates based on outdated species concepts has caused much taxonomic confusion, particularly in the plant pathology literature. A multilocus DNA sequence analysis (ITS, GAPDH, CHS-1, HIS3, ACT, TUB2) of 83 isolates of C. destructivum and related species revealed 16 clades that are recognised as separate species in the C. destructivum complex, which includes C. destructivum, C. fuscum, C. higginsianum, C. lini and C. tabacum. Each of these species is lecto-, epi- or neotypified in this study. Additionally, eight species, namely C. americae-borealis, C. antirrhinicola, C. bryoniicola, C. lentis, C. ocimi, C. pisicola, C. utrechtense and C. vignae are newly described. PMID:25492986

Characterization and potential of plant growth promoting rhizobacteria isolated from native Andean crops.

PubMed

Ogata-Gutiérrez, Katty; Chumpitaz-Segovia, Carolina; Lirio-Paredes, Jesus; Finetti-Sialer, Mariella M; Zúñiga-Dávila, Doris

2017-10-27

Bacteria isolated from soil and rhizosphere samples collected in Peru from Andean crops were tested in vitro and in vivo to determine their potential as plant growth promoters and their ability to induce systemic resistance to Alternaria alternata in tomato plants. The isolates were identified by sequencing their 16S ribosomal RNA gene. Test for phosphate solubilization, and indolacetic acid were also carried out, together with in vitro antagonism assays in dual cultures towards the plant pathogens Fusarium solani, A. alternata and Curvularia lunata. The three most promising isolates (Pa15, Ps155, Ps168) belonged to the genus Pseudomonas. Further assays were carried out with tomato plants to assess their plant protection effect towards A. alternata and as growth promoters. Inoculation of tomato seeds with all isolates significantly enhanced seed germination, plantlets emergence and plant development. Bacterial inoculation also reduce damage level caused by A. alternata. The expression levels of three tomato genes involved in the jasmonate (AOS), ethylene responsive (ERF-2) and pathogenesis related (PR-P2) pathways were determined in plants challenged with A. alternata, alone or with each bacterial isolate, respectively. Results showed that at 24 h after infection, in absence of the pathogen, the expression level of the tested genes was very low. The presence of A. alternata alone and in combination with bacteria increased the transcripts of all genes. Data showed a potential of best performing isolate Ps168 to sustain tomato plants nutrition and activate defense-related genes for protection by pathogenic fungi.

Insights into molecular and metabolic events associated with fruit response to post-harvest fungal pathogens

PubMed Central

Alkan, Noam; Fortes, Ana M.

2015-01-01

Due to post-harvest losses more than 30% of harvested fruits will not reach the consumers’ plate. Fungal pathogens play a key role in those losses, as they cause most of the fruit rots and the customer complaints. Many of the fungal pathogens are already present in the unripe fruit but remain quiescent during fruit growth until a particular phase of fruit ripening and senescence. The pathogens sense the developmental change and switch into the devastating necrotrophic life style that causes fruit rotting. Colonization of unripe fruit by the fungus initiates defensive responses that limit fungal growth and development. However, during fruit ripening several physiological processes occur that correlate with increased fruit susceptibility. In contrast to plant defenses in unripe fruit, the defense posture of ripe fruit entails a different subset of defense responses that will end with fruit rotting and losses. This review will focus on several aspects of molecular and metabolic events associated with fleshy fruit responses induced by post-harvest fungal pathogens during fruit ripening. PMID:26539204

Plant immunity triggered by engineered in vivo release of oligogalacturonides, damage-associated molecular patterns.

PubMed

Benedetti, Manuel; Pontiggia, Daniela; Raggi, Sara; Cheng, Zhenyu; Scaloni, Flavio; Ferrari, Simone; Ausubel, Frederick M; Cervone, Felice; De Lorenzo, Giulia

2015-04-28

Oligogalacturonides (OGs) are fragments of pectin that activate plant innate immunity by functioning as damage-associated molecular patterns (DAMPs). We set out to test the hypothesis that OGs are generated in planta by partial inhibition of pathogen-encoded polygalacturonases (PGs). A gene encoding a fungal PG was fused with a gene encoding a plant polygalacturonase-inhibiting protein (PGIP) and expressed in transgenic Arabidopsis plants. We show that expression of the PGIP-PG chimera results in the in vivo production of OGs that can be detected by mass spectrometric analysis. Transgenic plants expressing the chimera under control of a pathogen-inducible promoter are more resistant to the phytopathogens Botrytis cinerea, Pectobacterium carotovorum, and Pseudomonas syringae. These data provide strong evidence for the hypothesis that OGs released in vivo act as a DAMP signal to trigger plant immunity and suggest that controlled release of these molecules upon infection may be a valuable tool to protect plants against infectious diseases. On the other hand, elevated levels of expression of the chimera cause the accumulation of salicylic acid, reduced growth, and eventually lead to plant death, consistent with the current notion that trade-off occurs between growth and defense.

Control of plant defense mechanisms and fire blight pathogenesis through the regulation of 6-thioguanine biosynthesis in Erwinia amylovora.

PubMed

Coyne, Sébastien; Litomska, Agnieszka; Chizzali, Cornelia; Khalil, Mohammed N A; Richter, Klaus; Beerhues, Ludger; Hertweck, Christian

2014-02-10

Fire blight is a devastating disease of Rosaceae plants, such as apple and pear trees. It is characterized by necrosis of plant tissue, caused by the phytopathogenic bacterium Erwinia amylovora. The plant pathogen produces the well-known antimetabolite 6-thioguanine (6TG), which plays a key role in fire blight pathogenesis. Here we report that YcfR, a member of the LTTR family, is a major regulator of 6TG biosynthesis in E. amylovora. Inactivation of the regulator gene (ycfR) led to dramatically decreased 6TG production. Infection assays with apple plants (Malus domestica cultivar Holsteiner Cox) and cell cultures of Sorbus aucuparia (mountain ash, rowan) revealed abortive fire blight pathogenesis and reduced plant response (biphenyl and dibenzofuran phytoalexin production). In the presence of the ΔycfR mutant, apple trees were capable of activating the abscission machinery to remove infected tissue. In addition to unveiling the regulation of 6TG biosynthesis in a major plant pathogen, we demonstrate for the first time that this antimetabolite plays a pivotal role in dysregulating the plant response to infection. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Plant immunity triggered by engineered in vivo release of oligogalacturonides, damage-associated molecular patterns

PubMed Central

Benedetti, Manuel; Pontiggia, Daniela; Raggi, Sara; Cheng, Zhenyu; Scaloni, Flavio; Ferrari, Simone; Ausubel, Frederick M.; Cervone, Felice; De Lorenzo, Giulia

2015-01-01

Oligogalacturonides (OGs) are fragments of pectin that activate plant innate immunity by functioning as damage-associated molecular patterns (DAMPs). We set out to test the hypothesis that OGs are generated in planta by partial inhibition of pathogen-encoded polygalacturonases (PGs). A gene encoding a fungal PG was fused with a gene encoding a plant polygalacturonase-inhibiting protein (PGIP) and expressed in transgenic Arabidopsis plants. We show that expression of the PGIP–PG chimera results in the in vivo production of OGs that can be detected by mass spectrometric analysis. Transgenic plants expressing the chimera under control of a pathogen-inducible promoter are more resistant to the phytopathogens Botrytis cinerea, Pectobacterium carotovorum, and Pseudomonas syringae. These data provide strong evidence for the hypothesis that OGs released in vivo act as a DAMP signal to trigger plant immunity and suggest that controlled release of these molecules upon infection may be a valuable tool to protect plants against infectious diseases. On the other hand, elevated levels of expression of the chimera cause the accumulation of salicylic acid, reduced growth, and eventually lead to plant death, consistent with the current notion that trade-off occurs between growth and defense. PMID:25870275

Adaptive evolution has targeted the C-terminal domain of the RXLR effectors of plant pathogenic oomycetes.

PubMed

Win, Joe; Kamoun, Sophien

2008-04-01

Plant pathogenic microbes deliver effector proteins inside host cells to modulate plant defense circuitry and enable parasitic colonization. As genome sequences from plant pathogens become available, genome-wide evolutionary analyses will shed light on how pathogen effector genes evolved and adapted to the cellular environment of their host plants. In the August 2007 issue of Plant Cell, we described adaptive evolution (positive selection) in the cytoplasmic RXLR effectors of three recently sequenced oomycete plant pathogens. Here, we summarize our findings and describe additional data that further validate our approach.

Control of pome and stone fruit virus diseases.

PubMed

Barba, Marina; Ilardi, Vincenza; Pasquini, Graziella

2015-01-01

Many different systemic pathogens, including viruses, affect pome and stone fruits causing diseases with adverse effects in orchards worldwide. The significance of diseases caused by these pathogens on tree health and fruit shape and quality has resulted in the imposition of control measures both nationally and internationally. Control measures depend on the identification of diseases and their etiological agents. Diagnosis is the most important aspect of controlling fruit plant viruses. Early detection of viruses in fruit trees or in the propagative material is a prerequisite for their control and to guarantee a sustainable agriculture. Many quarantine programs are in place to reduce spread of viruses among countries during international exchange of germplasm. All these phytosanitary measures are overseen by governments based on agreements produced by international organizations. Also certification schemes applied to fruit trees allow the production of planting material of known variety and plant health status for local growers by controlling the propagation of pathogen-tested mother plants. They ensure to obtain propagative material not only free of "quarantine" organisms under the national legislation but also of important "nonquarantine" pathogens. The control of insect vectors plays an important role in the systemic diseases management, but it must be used together with other control measures as eradication of infected plants and use of certified propagation material. Apart from the control of the virus vector and the use of virus-free material, the development of virus-resistant cultivars appears to be the most effective approach to achieve control of plant viruses, especially for perennial crops that are more exposed to infection during their long life span. The use of resistant or tolerant cultivars and/or rootstocks could be potentially the most important aspect of virus disease management, especially in areas in which virus infections are endemic. The conventional breeding for virus-tolerant or resistant fruit tree cultivars using available germplasm is a long-term strategy, and the development and production of these cultivars may take decades, if successful. Genetic engineering allows the introduction of specific DNA sequences offering the opportunity to obtain existing fruit tree cultivars improved for the desired resistance trait. Unfortunately, genetic transformation of pome and stone fruits is still limited to few commercial genotypes. Research carried out and the new emerging biotechnological approaches to obtain fruit tree plants resistant or tolerant to viruses are discussed. © 2015 Elsevier Inc. All rights reserved.

Enzyme-driven metabolomic screening: a proof-of-principle method for discovery of plant defence compounds targeted by pathogens.

PubMed

Carere, Jason; Colgrave, Michelle L; Stiller, Jiri; Liu, Chunji; Manners, John M; Kazan, Kemal; Gardiner, Donald M

2016-11-01

Plants produce a variety of secondary metabolites to defend themselves from pathogen attack, while pathogens have evolved to overcome plant defences by producing enzymes that degrade or modify these defence compounds. However, many compounds targeted by pathogen enzymes currently remain enigmatic. Identifying host compounds targeted by pathogen enzymes would enable us to understand the potential importance of such compounds in plant defence and modify them to make them insensitive to pathogen enzymes. Here, a proof of concept metabolomics-based method was developed to discover plant defence compounds modified by pathogens using two pathogen enzymes with known targets in wheat and tomato. Plant extracts treated with purified pathogen enzymes were subjected to LC-MS, and the relative abundance of metabolites before and after treatment were comparatively analysed. Using two enzymes from different pathogens the in planta targets could be found by combining relatively simple enzymology with the power of untargeted metabolomics. Key to the method is dataset simplification based on natural isotope occurrence and statistical filtering, which can be scripted. The method presented here will aid in our understanding of plant-pathogen interactions and may lead to the development of new plant protection strategies. © 2016 CSIRO. New Phytologist © 2016 New Phytologist Trust.

Intersections between immune responses and morphological regulation in plants.

PubMed

Uchida, Naoyuki; Tasaka, Masao

2010-06-01

Successful plant pathogens have developed strategies to interfere with the defence mechanisms of their host plants through evolution. Conversely, host plants have evolved systems to counteract pathogen attack. Some pathogens induce pathogenic symptoms on plants that include morphological changes in addition to interference with plant growth. Recent studies, based on molecular biology and genetics using Arabidopsis thaliana, have revealed that factors derived from pathogens can modulate host systems and/or host factors that play important roles in the morphological regulation of host plants. Other reports, meanwhile, have shown that factors known to have roles in plant morphology also function in plant immune responses. Evolutionary conservation of these factors and systems implies that host-pathogen interactions and the evolution they drive have yielded tight links between morphological processes and immune responses. In this review, recent findings about these topics are introduced and discussed.

Aggressiveness of Cephalosporium maydis causing late wilt of maize in Spain.

PubMed

García-Carneros, A B; Girón, I; Molinero-Ruiz, L

2012-01-01

Late wilt of maize, caused by the vascular and soilborne pathogen Cephalosporium maydis, was identified in the Iberian Peninsula in 2008. During the last years the incidence and economical impact of the disease has importantly increased both in Portugal and Spain. Varieties of maize displaying tolerance to the pathogen are available, but the effectiveness can be dependent on the virulence of the fungus (i.e. ability to cause disease on a specific genotype). On the other hand, strains of crop pathogens from different geographic origins can differ with regard to the degree of disease caused on a specific genotype (i.e. aggressiveness). Our working hypothesis was that isolates of C. maydis from different maize growing areas may differ in aggressiveness towards maize plants. Seven fungal strains were isolated in 2009 from diseased plants collected in the most important maize growing regions of Spain and used to inoculate two susceptible maize varieties grown in shadehouse from March to July 2010. The experimental unit consisted of two 4-day-old seedlings planted in an 8-liter pot filled with sand/silt previously infested with 200 g of wheat grains colonized by the fungi. Non colonized wheat grains were used for the control treatments. Six replications (pots) were established for each variety/isolate combination according to a complete randomized 2 x 8 factorial design. The percentage of necrotic and dry aboveground tissues was recorded 14 weeks after inoculation and thereafter weekly until physiological senescence of the control plants. At the end of the experiment, weights of roots and aboveground parts of the plants were recorded. Initial occurrence of symptoms in the plants was significantly dependent on the isolate of C. maydis and on the maize variety. However, final severity of aboveground symptoms (leaf necroses and drying up) was only dependent on the fungal isolate. All the isolates significantly reduced the root weight of both varieties of maize. The highest root weight reductions were also associated to a significant low weight of above-ground parts. Considering all the symptoms analysed and their progression in the maize plants, our results reveal that a diversity of aggressiveness exists among isolates of C. maydis. The need for a characterization of maize genotypes by their reaction against highly aggressive isolates of the fungus in the Iberian Peninsula is suggested. This study is a first step towards a recommendation of crop varieties that are tolerant to C. maydis in different areas of the Iberian Peninsula. Future research aims at studying the relationship between aggressiveness levels, molecular characteristics and geographical origin whithin C. maydis.

The Vascular Pathogen Verticillium longisporum Does Not Affect Water Relations and Plant Responses to Drought Stress of Its Host, Brassica napus.

PubMed

Lopisso, Daniel Teshome; Knüfer, Jessica; Koopmann, Birger; von Tiedemann, Andreas

2017-04-01

Verticillium longisporum is a host-specific vascular pathogen of oilseed rape (Brassica napus L.) that causes economic crop losses by impairing plant growth and inducing premature senescence. This study investigates whether plant damage through Verticillium stem striping is due to impaired plant water relations, whether V. longisporum affects responses of a susceptible B. napus variety to drought stress, and whether drought stress, in turn, affects plant responses to V. longisporum. Two-factorial experiments on a susceptible cultivar of B. napus infected or noninfected with V. longisporum and exposed to three watering levels (30, 60, and 100% field capacity) revealed that drought stress and V. longisporum impaired plant growth by entirely different mechanisms. Although both stresses similarly affected plant growth parameters (plant height, hypocotyl diameter, and shoot and root dry matter), infection of B. napus with V. longisporum did not affect any drought-related physiological or molecular genetic plant parameters, including transpiration rate, stomatal conductance, photosynthesis rate, water use efficiency, relative leaf water content, leaf proline content, or the expression of drought-responsive genes. Thus, this study provides comprehensive physiological and molecular genetic evidence explaining the lack of wilt symptoms in B. napus infected with V. longisporum. Likewise, drought tolerance of B. napus was unaffected by V. longisporum, as was the level of disease by drought conditions, thus excluding a concerted action of both stresses in the field. Although it is evident that drought and vascular infection with V. longisporum impair plant growth by different mechanisms, it remains to be determined by which other factors V. longisporum causes crop loss.

Proteomic analysis of ripening tomato fruit infected by Botrytis cinerea.

PubMed

Shah, Punit; Powell, Ann L T; Orlando, Ron; Bergmann, Carl; Gutierrez-Sanchez, Gerardo

2012-04-06

Botrytis cinerea, a model necrotrophic fungal pathogen that causes gray mold as it infects different organs on more than 200 plant species, is a significant contributor to postharvest rot in fresh fruit and vegetables, including tomatoes. By describing host and pathogen proteomes simultaneously in infected tissues, the plant proteins that provide resistance and allow susceptibility and the pathogen proteins that promote colonization and facilitate quiescence can be identified. This study characterizes fruit and fungal proteins solubilized in the B. cinerea-tomato interaction using shotgun proteomics. Mature green, red ripe wild type and ripening inhibited (rin) mutant tomato fruit were infected with B. cinerea B05.10, and the fruit and fungal proteomes were identified concurrently 3 days postinfection. One hundred eighty-six tomato proteins were identified in common among red ripe and red ripe-equivalent ripening inhibited (rin) mutant tomato fruit infected by B. cinerea. However, the limited infections by B. cinerea of mature green wild type fruit resulted in 25 and 33% fewer defense-related tomato proteins than in red and rin fruit, respectively. In contrast, the ripening stage of genotype of the fruit infected did not affect the secreted proteomes of B. cinerea. The composition of the collected proteins populations and the putative functions of the identified proteins argue for their role in plant-pathogen interactions.

Proposal to conserve the name Bipolaris against Cochliobolus (Ascomycota: Pleosporales: Pleosporaceae)

USDA-ARS?s Scientific Manuscript database

The fungal genera Bipolaris Shoemaker and Cochliobolus Drechsler have been applied to economically important plant pathogens causing diseases of cereal crops worldwide, especially southern corn leaf blight. There are major accounts of these genera including those incorporating molecular phylogenetic...

An Interspecies Comparative Analysis of the Predicted Secretomes of the Necrotrophic Plant Pathogens Sclerotinia sclerotiorum and Botrytis cinerea

PubMed Central

2015-01-01

Phytopathogenic fungi form intimate associations with host plant species and cause disease. To be successful, fungal pathogens communicate with a susceptible host through the secretion of proteinaceous effectors, hydrolytic enzymes and metabolites. Sclerotinia sclerotiorum and Botrytis cinerea are economically important necrotrophic fungal pathogens that cause disease on numerous crop species. Here, a powerful bioinformatics pipeline was used to predict the refined S. sclerotiorum and B. cinerea secretomes, identifying 432 and 499 proteins respectively. Analyses focusing on S. sclerotiorum revealed that 16% of the secretome encoding genes resided in small, sequence heterogeneous, gene clusters that were distributed over 13 of the 16 predicted chromosomes. Functional analyses highlighted the importance of plant cell hydrolysis, oxidation-reduction processes and the redox state to the S. sclerotiorum and B. cinerea secretomes and potentially host infection. Only 8% of the predicted proteins were distinct between the two secretomes. In contrast to S. sclerotiorum, the B. cinerea secretome lacked CFEM- or LysM-containing proteins. The 115 fungal and oomycete genome comparison identified 30 proteins specific to S. sclerotiorum and B. cinerea, plus 11 proteins specific to S. sclerotiorum and 32 proteins specific to B. cinerea. Expressed sequence tag (EST) and proteomic analyses showed that 246 S. sclerotiorum secretome encoding genes had EST support, including 101 which were only expressed in vitro and 49 which were only expressed in planta, whilst 42 predicted proteins were experimentally proven to be secreted. These detailed in silico analyses of two important necrotrophic pathogens will permit informed choices to be made when candidate effector proteins are selected for function analyses in planta. PMID:26107498

Evidence for maintenance of sex by pathogens in plants.

PubMed

Busch, Jeremiah W; Neiman, Maurine; Koslow, Jennifer M

2004-11-01

The predominance of outcrossing despite the substantial transmission advantage of self-fertilization remains a paradox. Theory suggests that selection can favor outcrossing if it enables the production of offspring that are less susceptible to pathogen attack than offspring produced via self-fertilization. Thus, if pathogen pressure is contributing to the maintenance of outcrossing in plants, there may be a positive correlation between the number of pathogen species attacking plant species and the outcrossing rate of the plant species. We tested this hypothesis by examining the association between outcrossing rate and the number of fungal pathogen species that attack a large, taxonomically diverse set of seed plants. We show that plant species attacked by more fungal pathogen species have higher outcrossing rates than plants with fewer enemies. This relationship persists after correcting for study bias among natural and agricultural species of plants. We also accounted for the nested hierarchy of relationships among plant lineages by conducting phylogenetically independent contrasts (PICs) within genera and families that were adequately represented in our dataset. A meta-analysis of the correlation between pathogen and outcrossing PICs shows that there is a positive correlation between pathogen species number and outcrossing rates. This pattern is consistent with the hypothesis that pathogen-mediated selection may contribute to the maintenance of outcrossing in species of seed plants.

Effects of consecutive monoculture of Pseudostellaria heterophylla on soil fungal community as determined by pyrosequencing

NASA Astrophysics Data System (ADS)

Wu, Linkun; Chen, Jun; Wu, Hongmiao; Wang, Juanying; Wu, Yanhong; Lin, Sheng; Khan, Muhammad Umar; Zhang, Zhongyi; Lin, Wenxiong

2016-05-01

Under consecutive monoculture, the biomass and quality of Pseudostellaria heterophylla declines significantly. In this study, a three-year field experiment was conducted to identify typical growth inhibition effects caused by extended monoculturing of P. heterophylla. Deep pyrosequencing was used to examine changes in the structure and composition of soil fungal community along a three-year gradient of monoculture. The results revealed a distinct separation between the newly planted plot and the two-year, three-year monocultured plots. The Shannon and Simpson diversity indices were significantly higher in the two-year and three-year monoculture soils than in the newly planted soil. Consecutive monoculture of this plant led to a significant increase in relative abundance of Fusarium, Trichocladium and Myrothecium and Simplicillium, etc., but a significant decrease in the relative abundance of Penicillium. Quantitative PCR analysis confirmed a significant increase in Fusarium oxysporum, an agent known to cause wilt and rot disease of P. heterophylla. Furthermore, phenolic acid mixture at a ratio similar to that found in the rhizosphere could promote mycelial growth of pathogenic F. oxysporum. Overall, this study demonstrated that consecutive monoculture of P. heterophylla can alter the fungal community in the rhizosphere, including enrichment of host-specific pathogenic fungi at the expense of plant-beneficial fungi.

Cycloate, an inhibitor of fatty acid elongase, modulates the metabolism of very-long-side-chain alkylresorcinols in rye seedlings.

PubMed

Magnucka, Elzbieta G; Suzuki, Yoshikatsu; Pietr, Stanislaw J; Kozubek, Arkadiusz; Zarnowski, Robert

2009-10-01

Cycloate inhibits the biosynthesis of very-long-chain fatty acids, the essential constituents of plant waxes and suberin. Fatty acids also serve as precursors of aliphatic carbon chains in resorcinolic lipids, which play a fundamental role in the plant defence system against fungal pathogens. In this study, the effect of cycloate on the biosynthesis of 5-n-alkylresorcinols in rye seedlings (Secale cereale L.) grown under various light and thermal conditions was examined. The content of alkylresorcinols biosynthesised in rye was generally increased by the herbicide in both green and etiolated plants. The presence of cycloate also affected patterns of alkylresorcinol homologues in plants grown at 15 and 22 degrees C; very-long-side-chain compounds were less abundant, whereas both short-chain saturated and unsaturated homologues were generally accumulated. No cycloate-related effects caused by homologue pattern modifications were observed at elevated temperature. This study extends present understanding of the mode of action of thiocarbamate herbicides. Cycloate markedly affected the biosynthesis of very-long-side-chain resorcinolic lipids in rye seedlings, confirming the existence of parallels in both fatty acid and alkylresorcinol biosynthetic pathways. The observed cycloate-driven accumulation of 5-n-alkylresorcinols may improve the resistance of cereals to infections caused by microbial pathogens. Copyright 2009 Society of Chemical Industry.

Combining Inferential and Deductive Approaches to Estimate the Potential Geographical Range of the Invasive Plant Pathogen, Phytophthora ramorum

PubMed Central

Ireland, Kylie B.; Hardy, Giles E. St. J.; Kriticos, Darren J.

2013-01-01

Phytophthora ramorum, an invasive plant pathogen of unknown origin, causes considerable and widespread damage in plant industries and natural ecosystems of the USA and Europe. Estimating the potential geographical range of P. ramorum has been complicated by a lack of biological and geographical data with which to calibrate climatic models. Previous attempts to do so, using either invaded range data or surrogate species approaches, have delivered varying results. A simulation model was developed using CLIMEX to estimate the global climate suitability patterns for establishment of P. ramorum. Growth requirements and stress response parameters were derived from ecophysiological laboratory observations and site-level transmission and disease factors related to climate data in the field. Geographical distribution data from the USA (California and Oregon) and Norway were reserved from model-fitting and used to validate the models. The model suggests that the invasion of P. ramorum in both North America and Europe is still in its infancy and that it is presently occupying a small fraction of its potential range. Phytophthora ramorum appears to be climatically suited to large areas of Africa, Australasia and South America, where it could cause biodiversity and economic losses in plant industries and natural ecosystems with susceptible hosts if introduced. PMID:23667628

Can vessel dimension explain tolerance toward fungal vascular wilt diseases in woody plants? Lessons from Dutch elm disease and esca disease in grapevine

PubMed Central

Pouzoulet, Jérôme; Pivovaroff, Alexandria L.; Santiago, Louis S.; Rolshausen, Philippe E.

2014-01-01

This review illuminates key findings in our understanding of grapevine xylem resistance to fungal vascular wilt diseases. Grapevine (Vitis spp.) vascular diseases such as esca, botryosphaeria dieback, and eutypa dieback, are caused by a set of taxonomically unrelated ascomycete fungi. Fungal colonization of the vascular system leads to a decline of the plant host because of a loss of the xylem function and subsequent decrease in hydraulic conductivity. Fungal vascular pathogens use different colonization strategies to invade and kill their host. Vitis vinifera cultivars display different levels of tolerance toward vascular diseases caused by fungi, but the plant defense mechanisms underlying those observations have not been completely elucidated. In this review, we establish a parallel between two vascular diseases, grapevine esca disease and Dutch elm disease, and argue that the former should be viewed as a vascular wilt disease. Plant genotypes exhibit differences in xylem morphology and resistance to fungal pathogens causing vascular wilt diseases. We provide evidence that the susceptibility of three commercial V. vinifera cultivars to esca disease is correlated to large vessel diameter. Additionally, we explore how xylem morphological traits related to water transport are influenced by abiotic factors, and how these might impact host tolerance of vascular wilt fungi. Finally, we explore the utility of this concept for predicting which V. vinifera cultivars are most vulnerable of fungal vascular wilt diseases and propose new strategies for disease management. PMID:24971084

Multi-locus tree and species tree approaches toward resolving a complex clade of downy mildews (Straminipila, Oomycota), including pathogens of beet and spinach.

PubMed

Choi, Young-Joon; Klosterman, Steven J; Kummer, Volker; Voglmayr, Hermann; Shin, Hyeon-Dong; Thines, Marco

2015-05-01

Accurate species determination of plant pathogens is a prerequisite for their control and quarantine, and further for assessing their potential threat to crops. The family Peronosporaceae (Straminipila; Oomycota) consists of obligate biotrophic pathogens that cause downy mildew disease on angiosperms, including a large number of cultivated plants. In the largest downy mildew genus Peronospora, a phylogenetically complex clade includes the economically important downy mildew pathogens of spinach and beet, as well as the type species of the genus Peronospora. To resolve this complex clade at the species level and to infer evolutionary relationships among them, we used multi-locus phylogenetic analysis and species tree estimation. Both approaches discriminated all nine currently accepted species and revealed four previously unrecognized lineages, which are specific to a host genus or species. This is in line with a narrow species concept, i.e. that a downy mildew species is associated with only a particular host plant genus or species. Instead of applying the dubious name Peronospora farinosa, which has been proposed for formal rejection, our results provide strong evidence that Peronospora schachtii is an independent species from lineages on Atriplex and apparently occurs exclusively on Beta vulgaris. The members of the clade investigated, the Peronospora rumicis clade, associate with three different host plant families, Amaranthaceae, Caryophyllaceae, and Polygonaceae, suggesting that they may have speciated following at least two recent inter-family host shifts, rather than contemporary cospeciation with the host plants. Copyright © 2015 Elsevier Inc. All rights reserved.

Genomic characterization of plant cell wall degrading enzymes and in silico analysis of xylanases and polygalacturonases of Fusarium virguliforme.

PubMed

Chang, Hao-Xun; Yendrek, Craig R; Caetano-Anolles, Gustavo; Hartman, Glen L

2016-07-12

Plant cell wall degrading enzymes (PCWDEs) are a subset of carbohydrate-active enzymes (CAZy) produced by plant pathogens to degrade plant cell walls. To counteract PCWDEs, plants release PCWDEs inhibitor proteins (PIPs) to reduce their impact. Several transgenic plants expressing exogenous PIPs that interact with fungal glycoside hydrolase (GH)11-type xylanases or GH28-type polygalacturonase (PG) have been shown to enhance disease resistance. However, many plant pathogenic Fusarium species were reported to escape PIPs inhibition. Fusarium virguliforme is a soilborne pathogen that causes soybean sudden death syndrome (SDS). Although the genome of F. virguliforme was sequenced, there were limited studies focused on the PCWDEs of F. virguliforme. Our goal was to understand the genomic CAZy structure of F. viguliforme, and determine if exogenous PIPs could be theoretically used in soybean to enhance resistance against F. virguliforme. F. virguliforme produces diverse CAZy to degrade cellulose and pectin, similar to other necrotorphic and hemibiotrophic plant pathogenic fungi. However, some common CAZy of plant pathogenic fungi that catalyze hemicellulose, such as GH29, GH30, GH44, GH54, GH62, and GH67, were deficient in F. virguliforme. While the absence of these CAZy families might be complemented by other hemicellulases, F. virguliforme contained unique families including GH131, polysaccharide lyase (PL) 9, PL20, and PL22 that were not reported in other plant pathogenic fungi or oomycetes. Sequence analysis revealed two GH11 xylanases of F. virguliforme, FvXyn11A and FvXyn11B, have conserved residues that allow xylanase inhibitor protein I (XIP-I) binding. Structural modeling suggested that FvXyn11A and FvXyn11B could be blocked by XIP-I that serves as good candidate for developing transgenic soybeans. In contrast, one GH28 PG, FvPG2, contains an amino acid substitution that is potentially incompatible with the bean polygalacturonase-inhibitor protein II (PvPGIP2). Identification and annotation of CAZy provided advanced understanding of genomic composition of PCWDEs in F. virguliforme. Sequence and structural analyses of FvXyn11A and FvXyn11B suggested both xylanases were conserved in residues that allow XIP-I inhibition, and expression of both xylanases were detected during soybean roots infection. We postulate that a transgenic soybean expressing wheat XIP-I may be useful for developing root rot resistance to F. virguliforme.

Ralstonia solanacearum uses inorganic nitrogen metabolism for virulence, ATP production, and detoxification in the oxygen-limited host xylem environment.

PubMed

Dalsing, Beth L; Truchon, Alicia N; Gonzalez-Orta, Enid T; Milling, Annett S; Allen, Caitilyn

2015-03-17

Genomic data predict that, in addition to oxygen, the bacterial plant pathogen Ralstonia solanacearum can use nitrate (NO3(-)), nitrite (NO2(-)), nitric oxide (NO), and nitrous oxide (N2O) as terminal electron acceptors (TEAs). Genes encoding inorganic nitrogen reduction were highly expressed during tomato bacterial wilt disease, when the pathogen grows in xylem vessels. Direct measurements found that tomato xylem fluid was low in oxygen, especially in plants infected by R. solanacearum. Xylem fluid contained ~25 mM NO3(-), corresponding to R. solanacearum's optimal NO3(-) concentration for anaerobic growth in vitro. We tested the hypothesis that R. solanacearum uses inorganic nitrogen species to respire and grow during pathogenesis by making deletion mutants that each lacked a step in nitrate respiration (ΔnarG), denitrification (ΔaniA, ΔnorB, and ΔnosZ), or NO detoxification (ΔhmpX). The ΔnarG, ΔaniA, and ΔnorB mutants grew poorly on NO3(-) compared to the wild type, and they had reduced adenylate energy charge levels under anaerobiosis. While NarG-dependent NO3(-) respiration directly enhanced growth, AniA-dependent NO2(-) reduction did not. NO2(-) and NO inhibited growth in culture, and their removal depended on denitrification and NO detoxification. Thus, NO3(-) acts as a TEA, but the resulting NO2(-) and NO likely do not. None of the mutants grew as well as the wild type in planta, and strains lacking AniA (NO2(-) reductase) or HmpX (NO detoxification) had reduced virulence on tomato. Thus, R. solanacearum exploits host NO3(-) to respire, grow, and cause disease. Degradation of NO2(-) and NO is also important for successful infection and depends on denitrification and NO detoxification systems. The plant-pathogenic bacterium Ralstonia solanacearum causes bacterial wilt, one of the world's most destructive crop diseases. This pathogen's explosive growth in plant vascular xylem is poorly understood. We used biochemical and genetic approaches to show that R. solanacearum rapidly depletes oxygen in host xylem but can then respire using host nitrate as a terminal electron acceptor. The microbe uses its denitrification pathway to detoxify the reactive nitrogen species nitrite (a product of nitrate respiration) and nitric oxide (a plant defense signal). Detoxification may play synergistic roles in bacterial wilt virulence by converting the host's chemical weapon into an energy source. Mutant bacterial strains lacking elements of the denitrification pathway could not grow as well as the wild type in tomato plants, and some mutants were also reduced in virulence. Our results show how a pathogen's metabolic activity can alter the host environment in ways that increase pathogen success. Copyright © 2015 Dalsing et al.

Emerging infectious diseases of plants: pathogen pollution, climate change and agrotechnology drivers.

PubMed

Anderson, Pamela K; Cunningham, Andrew A; Patel, Nikkita G; Morales, Francisco J; Epstein, Paul R; Daszak, Peter

2004-10-01

Emerging infectious diseases (EIDs) pose threats to conservation and public health. Here, we apply the definition of EIDs used in the medical and veterinary fields to botany and highlight a series of emerging plant diseases. We include EIDs of cultivated and wild plants, some of which are of significant conservation concern. The underlying cause of most plant EIDs is the anthropogenic introduction of parasites, although severe weather events are also important drivers of disease emergence. Much is known about crop plant EIDs, but there is little information about wild-plant EIDs, suggesting that their impact on conservation is underestimated. We conclude with recommendations for improving strategies for the surveillance and control of plant EIDs.

Nonhost resistance to rust pathogens – a continuation of continua

PubMed Central

Bettgenhaeuser, Jan; Gilbert, Brian; Ayliffe, Michael; Moscou, Matthew J.

2014-01-01

The rust fungi (order: Pucciniales) are a group of widely distributed fungal plant pathogens, which can infect representatives of all vascular plant groups. Rust diseases significantly impact several crop species and considerable research focuses on understanding the basis of host specificity and nonhost resistance. Like many pathogens, rust fungi vary considerably in the number of hosts they can infect, such as wheat leaf rust (Puccinia triticina), which can only infect species in the genera Triticum and Aegilops, whereas Asian soybean rust (Phakopsora pachyrhizi) is known to infect over 95 species from over 42 genera. A greater understanding of the genetic basis determining host range has the potential to identify sources of durable resistance for agronomically important crops. Delimiting the boundary between host and nonhost has been complicated by the quantitative nature of phenotypes in the transition between these two states. Plant–pathogen interactions in this intermediate state are characterized either by (1) the majority of accessions of a species being resistant to the rust or (2) the rust only being able to partially complete key components of its life cycle. This leads to a continuum of disease phenotypes in the interaction with different plant species, observed as a range from compatibility (host) to complete immunity within a species (nonhost). In this review we will highlight how the quantitative nature of disease resistance in these intermediate interactions is caused by a continuum of defense barriers, which a pathogen needs to overcome for successfully establishing itself in the host. To illustrate continua as this underlying principle, we will discuss the advances that have been made in studying nonhost resistance towards rust pathogens, particularly cereal rust pathogens. PMID:25566270

De novo genome assembly of the soil-borne fungus and tomato pathogen Pyrenochaeta lycopersici

PubMed Central

2014-01-01

Background Pyrenochaeta lycopersici is a soil-dwelling ascomycete pathogen that causes corky root rot disease in tomato (Solanum lycopersicum) and other Solanaceous crops, reducing fruit yields by up to 75%. Fungal pathogens that infect roots receive less attention than those infecting the aerial parts of crops despite their significant impact on plant growth and fruit production. Results We assembled a 54.9Mb P. lycopersici draft genome sequence based on Illumina short reads, and annotated approximately 17,000 genes. The P. lycopersici genome is closely related to hemibiotrophs and necrotrophs, in agreement with the phenotypic characteristics of the fungus and its lifestyle. Several gene families related to host–pathogen interactions are strongly represented, including those responsible for nutrient absorption, the detoxification of fungicides and plant cell wall degradation, the latter confirming that much of the genome is devoted to the pathogenic activity of the fungus. We did not find a MAT gene, which is consistent with the classification of P. lycopersici as an imperfect fungus, but we observed a significant expansion of the gene families associated with heterokaryon incompatibility (HI). Conclusions The P. lycopersici draft genome sequence provided insight into the molecular and genetic basis of the fungal lifestyle, characterizing previously unknown pathogenic behaviors and defining strategies that allow this asexual fungus to increase genetic diversity and to acquire new pathogenic traits. PMID:24767544

Efficacy of water treatment processes and endemic gastrointestinal illness - A multi-city study in Sweden.

PubMed

Tornevi, Andreas; Simonsson, Magnus; Forsberg, Bertil; Säve-Söderbergh, Melle; Toljander, Jonas

2016-10-01

Outbreaks of acute gastrointestinal illnesses (AGI) have been linked to insufficient drinking water treatment on numerous occasions in the industrialized world, but it is largely unknown to what extent public drinking water influences the endemic level of AGI. This paper aimed to examine endemic AGI and the relationship with pathogen elimination efficacy in public drinking water treatment processes. For this reason, time series data of all telephone calls to the Swedish National Healthcare Guide between November 2007 and February 2014 from twenty Swedish cities were obtained. Calls concerning vomiting, diarrhea or abdominal pain (AGI calls) were separated from other concerns (non-AGI calls). Information on which type of microbial barriers each drinking water treatment plant in these cities have been used were obtained, together with the barriers' theoretical pathogen log reduction efficacy. The total log reduction in the drinking water plants varied between 0.0 and 6.1 units for viruses, 0.0-14.6 units for bacteria and 0.0-7.3 units regarding protozoans. To achieve one general efficacy parameter for each plant, a weighted mean value of the log reductions (WLR) was calculated, with the weights based on how commonly these pathogen groups cause AGI. The WLR in the plants varied between 0.0 and 6.4 units. The effect of different pathogen elimination efficacy on levels of AGI calls relative non-AGI calls was evaluated in regression models, controlling for long term trends, population size, age distribution, and climatological area. Populations receiving drinking water produced with higher total log reduction was associated with a lower relative number of AGI calls. In overall, AGI calls decreased by 4% (OR = 0.96, CI: 0.96-0.97) for each unit increase in the WLR. The findings apply to both groundwater and surface water study sites, but are particularly evident among surface water sites during seasons when viruses are the main cause of AGI. This study proposes that the endemic level of gastroenteritis can indeed be reduced with more advanced treatment processes at many municipal drinking water treatment plants. Copyright © 2016 Elsevier Ltd. All rights reserved.

Multiple Candidate Effectors from the Oomycete Pathogen Hyaloperonospora arabidopsidis Suppress Host Plant Immunity

PubMed Central

Fabro, Georgina; Steinbrenner, Jens; Coates, Mary; Ishaque, Naveed; Baxter, Laura; Studholme, David J.; Körner, Evelyn; Allen, Rebecca L.; Piquerez, Sophie J. M.; Rougon-Cardoso, Alejandra; Greenshields, David; Lei, Rita; Badel, Jorge L.; Caillaud, Marie-Cecile; Sohn, Kee-Hoon; Van den Ackerveken, Guido; Parker, Jane E.; Beynon, Jim; Jones, Jonathan D. G.

2011-01-01

Oomycete pathogens cause diverse plant diseases. To successfully colonize their hosts, they deliver a suite of effector proteins that can attenuate plant defenses. In the oomycete downy mildews, effectors carry a signal peptide and an RxLR motif. Hyaloperonospora arabidopsidis (Hpa) causes downy mildew on the model plant Arabidopsis thaliana (Arabidopsis). We investigated if candidate effectors predicted in the genome sequence of Hpa isolate Emoy2 (HaRxLs) were able to manipulate host defenses in different Arabidopsis accessions. We developed a rapid and sensitive screening method to test HaRxLs by delivering them via the bacterial type-three secretion system (TTSS) of Pseudomonas syringae pv tomato DC3000-LUX (Pst-LUX) and assessing changes in Pst-LUX growth in planta on 12 Arabidopsis accessions. The majority (∼70%) of the 64 candidates tested positively contributed to Pst-LUX growth on more than one accession indicating that Hpa virulence likely involves multiple effectors with weak accession-specific effects. Further screening with a Pst mutant (ΔCEL) showed that HaRxLs that allow enhanced Pst-LUX growth usually suppress callose deposition, a hallmark of pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). We found that HaRxLs are rarely strong avirulence determinants. Although some decreased Pst-LUX growth in particular accessions, none activated macroscopic cell death. Fewer HaRxLs conferred enhanced Pst growth on turnip, a non-host for Hpa, while several reduced it, consistent with the idea that turnip's non-host resistance against Hpa could involve a combination of recognized HaRxLs and ineffective HaRxLs. We verified our results by constitutively expressing in Arabidopsis a sub-set of HaRxLs. Several transgenic lines showed increased susceptibility to Hpa and attenuation of Arabidopsis PTI responses, confirming the HaRxLs' role in Hpa virulence. This study shows TTSS screening system provides a useful tool to test whether candidate effectors from eukaryotic pathogens can suppress/trigger plant defense mechanisms and to rank their effectiveness prior to subsequent mechanistic investigation. PMID:22072967

Expression of apoplast-targeted plant defensin MtDef4.2 confers resistance to leaf rust pathogen Puccinia triticina but does not affect mycorrhizal symbiosis in transgenic wheat

USDA-ARS?s Scientific Manuscript database

Rust diseases caused by Puccinia spp. pose a major threat to global wheat production. Puccinia triticina (Pt), an obligate basidiomycete biotroph, causes leaf rust disease which incurs yield losses of up to 50% in wheat. Historically, resistant wheat cultivars have been used to control leaf rust, bu...

Perspectives on the Transition From Bacterial Phytopathogen Genomics Studies to Applications Enhancing Disease Management: From Promise to Practice.

PubMed

Sundin, George W; Wang, Nian; Charkowski, Amy O; Castiblanco, Luisa F; Jia, Hongge; Zhao, Youfu

2016-10-01

The advent of genomics has advanced science into a new era, providing a plethora of "toys" for researchers in many related and disparate fields. Genomics has also spawned many new fields, including proteomics and metabolomics, furthering our ability to gain a more comprehensive view of individual organisms and of interacting organisms. Genomic information of both bacterial pathogens and their hosts has provided the critical starting point in understanding the molecular bases of how pathogens disrupt host cells to cause disease. In addition, knowledge of the complete genome sequence of the pathogen provides a potentially broad slate of targets for the development of novel virulence inhibitors that are desperately needed for disease management. Regarding plant bacterial pathogens and disease management, the potential for utilizing genomics resources in the development of durable resistance is enhanced because of developing technologies that enable targeted modification of the host. Here, we summarize the role of genomics studies in furthering efforts to manage bacterial plant diseases and highlight novel genomics-enabled strategies heading down this path.

Occurrence of downy mildews on ornamental plants and their control by chemical compounds.

PubMed

Skrzypczak, C

2007-01-01

The downy mildew on Coreopsis grandiflora caused by Plasmopara halstedii was observed during summer, mainly in July and August. Symptoms of the disease were first seen on external leaves and progressively spread to inner parts of plant rosette. On Alyssum saxatile downy mildew symptoms induced by Peronospora parasitica were observed during whole vegetation period with the strongest expression in early spring and late summer. Amistar 250 SC (25% azoxystrobine), Mildex 711,9 WG (66.7% phosethyl aluminium + 4.4% fenamidone), Previcur Energy 840 SL (530 g/l propamocarb + 310 g/l phosetyl aluminium) and Tanos 50 WG (25% cymoxanil + 25% famoxate) were used for pathogens control. In the protection of Coreopsis grandiflora against P. halstedii all tested compounds, applied curatively, decreased sporulation of the pathogen. On treaded plants at least 4-time less leaves were diseased. In the control of P. parasitica on Alyssum saxatile, the smallest number of swallowed structures on leaves was noticed on plants treated with azoxystrobine at conc. 250 microg/cm3.

Molecular biology of potyviruses.

PubMed

Revers, Frédéric; García, Juan Antonio

2015-01-01

Potyvirus is the largest genus of plant viruses causing significant losses in a wide range of crops. Potyviruses are aphid transmitted in a nonpersistent manner and some of them are also seed transmitted. As important pathogens, potyviruses are much more studied than other plant viruses belonging to other genera and their study covers many aspects of plant virology, such as functional characterization of viral proteins, molecular interaction with hosts and vectors, structure, taxonomy, evolution, epidemiology, and diagnosis. Biotechnological applications of potyviruses are also being explored. During this last decade, substantial advances have been made in the understanding of the molecular biology of these viruses and the functions of their various proteins. After a general presentation on the family Potyviridae and the potyviral proteins, we present an update of the knowledge on potyvirus multiplication, movement, and transmission and on potyvirus/plant compatible interactions including pathogenicity and symptom determinants. We end the review providing information on biotechnological applications of potyviruses. © 2015 Elsevier Inc. All rights reserved.

Involvement of bacterial TonB-dependent signaling in the generation of an oligogalacturonide damage-associated molecular pattern from plant cell walls exposed to Xanthomonas campestris pv. campestris pectate lyases

PubMed Central

2012-01-01

Background Efficient perception of attacking pathogens is essential for plants. Plant defense is evoked by molecules termed elicitors. Endogenous elicitors or damage-associated molecular patterns (DAMPs) originate from plant materials upon injury or pathogen activity. While there are comparably well-characterized examples for DAMPs, often oligogalacturonides (OGAs), generated by the activity of fungal pathogens, endogenous elicitors evoked by bacterial pathogens have been rarely described. In particular, the signal perception and transduction processes involved in DAMP generation are poorly characterized. Results A mutant strain of the phytopathogenic bacterium Xanthomonas campestris pv. campestris deficient in exbD2, which encodes a component of its unusual elaborate TonB system, had impaired pectate lyase activity and caused no visible symptoms for defense on the non-host plant pepper (Capsicum annuum). A co-incubation of X. campestris pv. campestris with isolated cell wall material from C. annuum led to the release of compounds which induced an oxidative burst in cell suspension cultures of the non-host plant. Lipopolysaccharides and proteins were ruled out as elicitors by polymyxin B and heat treatment, respectively. After hydrolysis with trifluoroacetic acid and subsequent HPAE chromatography, the elicitor preparation contained galacturonic acid, the monosaccharide constituent of pectate. OGAs were isolated from this crude elicitor preparation by HPAEC and tested for their biological activity. While small OGAs were unable to induce an oxidative burst, the elicitor activity in cell suspension cultures of the non-host plants tobacco and pepper increased with the degree of polymerization (DP). Maximal elicitor activity was observed for DPs exceeding 8. In contrast to the X. campestris pv. campestris wild type B100, the exbD2 mutant was unable to generate elicitor activity from plant cell wall material or from pectin. Conclusions To our knowledge, this is the second report on a DAMP generated by bacterial features. The generation of the OGA elicitor is embedded in a complex exchange of signals within the framework of the plant-microbe interaction of C. annuum and X. campestris pv. campestris. The bacterial TonB-system is essential for the substrate-induced generation of extracellular pectate lyase activity. This is the first demonstration that a TonB-system is involved in bacterial trans-envelope signaling in the context of a pathogenic interaction with a plant. PMID:23082751

The function of small RNAs in plant biotic stress response.

PubMed

Huang, Juan; Yang, Meiling; Zhang, Xiaoming

2016-04-01

Small RNAs (sRNAs) play essential roles in plants upon biotic stress. Plants utilize RNA silencing machinery to facilitate pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity to defend against pathogen attack or to facilitate defense against insect herbivores. Pathogens, on the other hand, are also able to generate effectors and sRNAs to counter the host immune response. The arms race between plants and pathogens/insect herbivores has triggered the evolution of sRNAs, RNA silencing machinery and pathogen effectors. A great number of studies have been performed to investigate the roles of sRNAs in plant defense, bringing in the opportunity to utilize sRNAs in plant protection. Transgenic plants with pathogen-derived resistance ability or transgenerational defense have been generated, which show promising potential as solutions for pathogen/insect herbivore problems in the field. Here we summarize the recent progress on the function of sRNAs in response to biotic stress, mainly in plant-pathogen/insect herbivore interaction, and the application of sRNAs in disease and insect herbivore control. © 2016 Institute of Botany, Chinese Academy of Sciences.

Biological Control of Aquatic Plants with Pathogenic Fungi

DTIC Science & Technology

1981-01-01

reverse side II necoosary and Ident•l•y by block number) Aquatic plant control Fungi Aquatic plants Pathogenic fungi Biological control Waterhyacinths...BACTERIA ............. ................. D1 2 1 BIOTIGICAL CONTROL OF AQUATIC PLANTS WITH PATHOGENIC FUNGI PART I: INTRODUCTION 1. Plant pathogens have...first noted in Florida. 13. In December of 1973, Dr. K. E. Ctnway isolated a Cercospora species, along with many other fungi , from declining

Development of shampoo, soap and ointment formulated by green synthesised silver nanoparticles functionalised with antimicrobial plants oils in veterinary dermatology: treatment and prevention strategies.

PubMed

Bansod, Sunita Dashrath; Bawaskar, Manisha Subrashrao; Gade, Aniket Krishnarao; Rai, Mahendra Kumar

2015-08-01

Many scientists have focused their research on the role of nanotechnology for the control of human pathogens, but there are also many topical pathogens present in animals, which infect animals and transfer to humans. Topical therapy is extremely important for the management of dermatological condition in animals. Therefore, the present study aims to evaluate the efficacy of biogenic silver nanoparticles (AgNPs) in combination with herbal oils against animal skin infections which may be responsible for causing infections in human beings. Here, the authors synthesised and characterised the AgNPs from Azadirachta indica. The oils were extracted from medicinal plants including Cymbopogon citratus, Cymbopogon martini, Eucalyptus globules, A. indica and Ocimum sanctum and the antifungal and antibacterial activity of plant oils along with AgNPs were evaluated. An excision wound model was used for the study of wound healing activity in rabbits. AgNPs functionalised oil has demonstrated remarkable antimicrobial activity against pathogens present on the skin of animals. The nano-functionalised antimicrobial oils were used in the formulation of shampoo, soap and ointment for veterinary dermatology. Antimicrobial products of plant origin with AgNPs are valuable, safe and have a specific role in controlling diseases. The authors believe that this approach will be a good alternative therapy to solve the continuous antibiotic resistance developed by many bacterial pathogens and will be utilised in various animal contacting areas in medicine.

Pathogen filtration to control plant disease outbreak in greenhouse production

NASA Astrophysics Data System (ADS)

Jeon, Sangho; Krasnow, Charles; Bhalsod, Gemini; Granke, Leah; Harlan, Blair; Hausbeck, Mary; Zhang, Wei

2016-04-01

Previous research has been extensively focused on understanding the fate and transport of human microbial pathogens in soil and water environments. However, little is known about the transport of plant pathogens, although these pathogens are often found in irrigation waters and could cause severe crop damage and economical loss. Water mold pathogens including Phytophthora spp. and Pythium spp. are infective to a wide range of vegetable and floriculture crops, and they are primarily harbored in soils and disseminated through water flow. It is challenging to control these pathogens because they often quickly develop resistance to many fungicides. Therefore, this multi-scale study aimed to investigate physical removal of plant pathogens from water by filtration, thus reducing the pathogen exposure risks to crops. In column-scale experiments, we studied controlling factors on the transport and retention of Phytophthora capsici zoospores in saturated columns packed with iron oxide coated-sand and uncoated-sand under varying solution chemistry. Biflagellate zoospores were less retained than encysted zoospores, and lower solution pH and greater iron oxide content increased the retention of encysted zoospores. These results provided insights on environmental dispersal of Phytophthora zoospores in natural soils as well as on developing cost-effective engineered filtration systems for pathogen removal. Using small-scale greenhouse filtration systems, we further investigated the performance of varying filter media (i.e., granular sand, iron oxide coated ceramic porous media, and activated carbon) in mitigating disease outbreaks of Phytophthora and Pythium for greenhouse-grown squash and poinsettia, respectively, in comparison with fungicide treatment. For squash, filtration by iron oxide coated media was more effective in reducing the Phytophthora infection, comparing to sand filtration and fungicide application. For poinsettia, sand filtration performed better in controlling the Pythium infection than fungicide application, and nutrient limitation in crops was observed under filtration by activated carbon. Overall, our results suggests that filtration of irrigation water can be effective in reducing crop disease outbreaks, while decreasing the use of fungicides and thus promoting the crop and environmental health.

Pivoting the Plant Immune System from Dissection to Deployment

PubMed Central

Dangl, Jeffery L.; Horvath, Diana M.; Staskawicz, Brian J.

2013-01-01

Diverse and rapidly evolving pathogens cause plant diseases and epidemics that threaten crop yield and food security around the world. Research over the last 25 years has led to an increasingly clear conceptual understanding of the molecular components of the plant immune system. Combined with ever-cheaper DNA-sequencing technology and the rich diversity of germ plasm manipulated for over a century by plant breeders, we now have the means to begin development of durable (long-lasting) disease resistance beyond the limits imposed by conventional breeding and in a manner that will replace costly and unsustainable chemical controls. PMID:23950531

Soft rot erwiniae: from genes to genomes.

PubMed

Toth, Ian K; Bell, Kenneth S; Holeva, Maria C; Birch, Paul R J

2003-01-01

SUMMARY The soft rot erwiniae, Erwinia carotovora ssp. atroseptica (Eca), E. carotovora ssp. carotovora (Ecc) and E. chrysanthemi (Ech) are major bacterial pathogens of potato and other crops world-wide. We currently understand much about how these bacteria attack plants and protect themselves against plant defences. However, the processes underlying the establishment of infection, differences in host range and their ability to survive when not causing disease, largely remain a mystery. This review will focus on our current knowledge of pathogenesis in these organisms and discuss how modern genomic approaches, including complete genome sequencing of Eca and Ech, may open the door to a new understanding of the potential subtlety and complexity of soft rot erwiniae and their interactions with plants. The soft rot erwiniae are members of the Enterobacteriaceae, along with other plant pathogens such as Erwinia amylovora and human pathogens such as Escherichia coli, Salmonella spp. and Yersinia spp. Although the genus name Erwinia is most often used to describe the group, an alternative genus name Pectobacterium was recently proposed for the soft rot species. Ech mainly affects crops and other plants in tropical and subtropical regions and has a wide host range that includes potato and the important model host African violet (Saintpaulia ionantha). Ecc affects crops and other plants in subtropical and temperate regions and has probably the widest host range, which also includes potato. Eca, on the other hand, has a host range limited almost exclusively to potato in temperate regions only. Disease symptoms: Soft rot erwiniae cause general tissue maceration, termed soft rot disease, through the production of plant cell wall degrading enzymes. Environmental factors such as temperature, low oxygen concentration and free water play an essential role in disease development. On potato, and possibly other plants, disease symptoms may differ, e.g. blackleg disease is associated more with Eca and Ech than with Ecc. http://www.scri.sari.ac.uk/TiPP/Erwinia.htm, http://www.ahabs.wisc.edu:16080/ approximately pernalab/erwinia/index.htm, http://www.tigr.org/tdb/mdb/mdbinprogress.html, http://www.sanger.ac.uk/Projects/E_carotovora/.

The role of isoflavone metabolism in plant protection depends on the rhizobacterial MAMP that triggers systemic resistance against Xanthomonas axonopodis pv. glycines in Glycine max (L.) Merr. cv. Osumi.

PubMed

Algar, Elena; Gutierrez-Mañero, F Javier; Garcia-Villaraco, Ana; García-Seco, Daniel; Lucas, J Antonio; Ramos-Solano, Beatriz

2014-09-01

Glycine max (L.) Merr. plays a crucial role in both the field of food and the pharmaceutical industry due to their input as plant protein and to the benefits of isoflavones (IF) for health. In addition, IF play a key role in nodulation and plant defense and therefore, an increase in IF would be desirable for better field performance. IF are secondary metabolites and therefore, inducible, so finding effective agents to increase IF contents is interesting. Among these agents, plant growth promoting rhizobacteria (PGPR) have been used to trigger systemic induction of plant's secondary metabolism through their microbe associated molecular patterns (MAMPs) that fit in the plant's receptors to start a systemic response. The aim of this study was to evaluate the ability of 4 PGPR that had a contrasted effect on IF metabolism, to protect plants against biotic stress and to establish the relation between IF profile and the systemic response triggered by the bacteria. Apparently, the response involves a lower sensitivity to ethylene and despite the decrease in effective photosynthesis, growth is only compromised in the case of M84, the most effective in protection. All strains protected soybean against Xanthomonas axonopodis pv. glycines (M84 > N5.18 > Aur9>N21.4) and only M84 and N5.18 involved IF. N5.18 stimulated accumulation of IF before pathogen challenge. M84 caused a significant increase on IF only after pathogen challenge and N21.4 caused a significant increase on IF content irrespective of pathogen challenge. Aur9 did not affect IF. These results point out that all 4 strains have MAMPs that trigger defensive metabolism in soybean. Protection induced by N21.4 and Aur9 involves other metabolites different to IF and the role of IF in defence depends on the previous metabolic status of the plant and on the bacterial MAMP. Copyright © 2014 Elsevier Masson SAS. All rights reserved.

Fire blight: applied genomic insights of the pathogen and host

USDA-ARS?s Scientific Manuscript database

The enterobacterial phytopathogen, Erwinia amylovora, causes fire blight, an invasive disease that threatens a wide range of commercial and ornamental Rosaceae host plants. The response elicited by E. amylovora in its host during disease development is similar to the hypersensitive reaction that ty...

Characterization of the Asian citrus psyllid transcriptome

USDA-ARS?s Scientific Manuscript database

The Asian citrus psyllid (Diaphorina citri Kuwayama) and other psyllids are important agricultural pests that cause extensive economic damage by feeding and as vectors of plant pathogens. No psyllid genomes have been characterized, and little is known about the composition of psyllid genomes or the ...

Pre- and postharvest fungal apple diseases

USDA-ARS?s Scientific Manuscript database

The domesticated apple (Malus domestica) is the most significant pome fruit grown and consumed worldwide. China is the largest producer followed by the United States on a global scale. However, fungal plant pathogens cause significant economic losses in the field and in storage which negatively impa...

The Downy Mildews: so many genomes, so little time

USDA-ARS?s Scientific Manuscript database

Downy mildews (DMs) are obligate biotrophic oomycete pathogens that cause diseases on a wide range of plant species. Individual species exhibit a high degree of host specialization. We have utilized next generation sequencing to efficiently generate de novo genome assemblies of multiple geographica...

Introduction to Oomycetes

USDA-ARS?s Scientific Manuscript database

The oomycetes, also known as “water molds”, are a group of several hundred organisms that include some of the most devastating plant pathogens. The diseases they cause include seedling blights, damping-off, root rots, foliar blights and downy mildews. Some notable diseases are the late blight of po...

Tolerance to Phytophthora Fruit Rot in Watermelon Plant Introductions

USDA-ARS?s Scientific Manuscript database

Phytophthora capsici is distributed worldwide, and is an aggressive pathogen with a broad host range infecting solanaceous, leguminaceous, and cucurbitaceous crops. Fruit rot, caused by P. capsici is an emerging disease in most watermelon producing regions of Southeast US. Resistance to fruit rot o...

Evolutionary dynamics of interactions between plants and their enemies: comparison of herbivorous insects and pathogens.

PubMed

Wininger, Kerry; Rank, Nathan

2017-11-01

Plants colonized land over 400 million years ago. Shortly thereafter, organisms began to consume terrestrial plant tissue as a nutritional resource. Most plant enemies are plant pathogens or herbivores, and they impose natural selection for plants to evolve defenses. These traits generate selection pressures on enemies. Coevolution between terrestrial plants and their enemies is an important element of the evolutionary history of both groups. However, coevolutionary studies of plant-pathogen interactions have tended to focus on different research topics than plant-herbivore interactions. Specifically, studies of plant-pathogen interactions often adopt a "gene-for-gene" conceptual framework. In contrast, studies of plants and herbivores often investigate escalation or elaboration of plant defense and herbivore adaptations to overcome it. The main exceptions to the general pattern are studies that focus on small, sessile herbivores that share many features with plant pathogens, studies that incorporate both herbivores and pathogens into a single investigation, and studies that test aspects of Thompson's geographic mosaic theory for coevolution. We discuss the implications of these findings for future research. © 2017 New York Academy of Sciences.

Pathogen profile update: Fusarium oxysporum.

PubMed

Michielse, Caroline B; Rep, Martijn

2009-05-01

Kingdom Fungi; Phylum Ascomycota; Class Sordariomycetes; Order Hypocreales; Family Nectriaceae; genus Fusarium. Very broad at the species level. More than 120 different formae speciales have been identified based on specificity to host species belonging to a wide range of plant families. Initial symptoms of vascular wilt include vein clearing and leaf epinasty, followed by stunting, yellowing of the lower leaves, progressive wilting, defoliation and, finally, death of the plant. On fungal colonization, the vascular tissue turns brown, which is clearly visible in cross-sections of the stem. Some formae speciales are not primarily vascular pathogens, but cause foot and root rot or bulb rot. Can cause severe losses in many vegetables and flowers, field crops, such as cotton, and plantation crops, such as banana, date palm and oil palm. Use of resistant varieties is the only practical measure for controlling the disease in the field. In glasshouses, soil sterilization can be performed. http://www.broad.mit.edu/annotation/genome/fusarium_group/MultiHome.html; http://www.fgsc.net/Fusarium/fushome.htm; http://www.phi-base.org/query.php

Fusarium Species and Their Associated Mycotoxins.

PubMed

Munkvold, Gary P

2017-01-01

The genus Fusarium includes numerous toxigenic species that are pathogenic to plants or humans, and are able to colonize a wide range of environments on earth. The genus comprises around 70 well-known species, identified by using a polyphasic approach, and as many as 300 putative species, according to phylogenetic species concepts; many putative species do not yet have formal names. Fusarium is one of the most economically important fungal genera because of yield loss due to plant pathogenic activity; mycotoxin contamination of food and feed products which often render them unaccep for marketing; and health impacts to humans and livestock, due to consumption of mycotoxins. Among the most important mycotoxins produced by species of Fusarium are the trichothecenes and the fumonisins. Fumonisins cause fatal livestock diseases and are considered potentially carcinogenic mycotoxins for humans, while trichothecenes are potent inhibitors of protein synthesis. This chapter summarizes the main aspects of morphology, pathology, and toxigenicity of the main Fusarium species that colonize different agricultural crops and environments worldwide, and cause mycotoxin contamination of food and feed.

Contribution of the Salmonella enterica KdgR Regulon to Persistence of the Pathogen in Vegetable Soft Rots

PubMed Central

George, Andrée S.; Salas González, Isai; Lorca, Graciela L.

2015-01-01

During their colonization of plants, human enteric pathogens, such as Salmonella enterica, are known to benefit from interactions with phytopathogens. At least in part, benefits derived by Salmonella from the association with a soft rot caused by Pectobacterium carotovorum were shown to be dependent on Salmonella KdgR, a regulator of genes involved in the uptake and utilization of carbon sources derived from the degradation of plant polymers. A Salmonella kdgR mutant was more fit in soft rots but not in the lesions caused by Xanthomonas spp. and Pseudomonas spp. Bioinformatic, phenotypic, and gene expression analyses demonstrated that the KdgR regulon included genes involved in uptake and metabolism of molecules resulting from pectin degradation as well as those central to the utilization of a number of other carbon sources. Mutant analyses indicated that the Entner-Doudoroff pathway, in part controlled by KdgR, was critical for the persistence within soft rots and likely was responsible for the kdgR phenotype. PMID:26682862

A whole genome analysis reveals the presence of a plant PR1 sequence in the potato pathogen Streptomyces scabies and other Streptomyces species.

PubMed

Armijos-Jaramillo, Vinicio; Santander-Gordón, Daniela; Soria, Rosa; Pazmiño-Betancourth, Mauro; Echeverría, María Cristina

2017-09-01

Streptomyces scabies is a common soil bacterium that causes scab symptoms in potatoes. Strong evidence indicates horizontal gene transfer (HGT) among bacteria has influenced the evolution of this plant pathogen and other Streptomyces spp. To extend the study of the HGT to the Streptomyces genus, we explored the effects of the inter-domain HGT in the S. scabies genome. We employed a semi-automatic pipeline based on BLASTp searches and phylogenetic reconstruction. The data show low impact of inter-domain HGT in the S. scabies genome; however, we found a putative plant pathogenesis related 1 (PR1) sequence in the genome of S. scabies and other species of the genus. It is possible that this gene could be used by S. scabies to out-compete other soil organisms. Copyright © 2016 Elsevier Inc. All rights reserved.

Optimization for rapid synthesis of silver nanoparticles and its effect on phytopathogenic fungi

NASA Astrophysics Data System (ADS)

Krishnaraj, C.; Ramachandran, R.; Mohan, K.; Kalaichelvan, P. T.

In this present study, silver nanoparticles were synthesized by green chemistry approach using Acalypha indica leaf extract as reducing agents. The reaction medium employed in the synthesis process was optimized to attain better yield, controlled size and stability. Further, the biosynthesized silver nanoparticles were conformed through UV-vis spectrum, XRD and HR-TEM analyses. Different concentration of silver nanoparticles were tested to know the inhibitory effect of fungal plant pathogens namely Alternaria alternata, Sclerotinia sclerotiorum, Macrophomina phaseolina, Rhizoctonia solani, Botrytis cinerea and Curvularia lunata. Interestingly, 15 mg concentration of silver nanoparticles showed excellent inhibitory activity against all the tested pathogens. Thus, the obtained results clearly suggest that silver nanoparticles may have important applications in controlling various plant diseases caused by fungi.

Induced Release of a Plant-Defense Volatile ‘Deceptively’ Attracts Insect Vectors to Plants Infected with a Bacterial Pathogen

PubMed Central

Mann, Rajinder S.; Ali, Jared G.; Hermann, Sara L.; Tiwari, Siddharth; Pelz-Stelinski, Kirsten S.; Alborn, Hans T.; Stelinski, Lukasz L.

2012-01-01

Transmission of plant pathogens by insect vectors is a complex biological process involving interactions between the plant, insect, and pathogen. Pathogen-induced plant responses can include changes in volatile and nonvolatile secondary metabolites as well as major plant nutrients. Experiments were conducted to understand how a plant pathogenic bacterium, Candidatus Liberibacter asiaticus (Las), affects host preference behavior of its psyllid (Diaphorina citri Kuwayama) vector. D. citri were attracted to volatiles from pathogen-infected plants more than to those from non-infected counterparts. Las-infected plants were more attractive to D. citri adults than non-infected plants initially; however after feeding, psyllids subsequently dispersed to non-infected rather than infected plants as their preferred settling point. Experiments with Las-infected and non-infected plants under complete darkness yielded similar results to those recorded under light. The behavior of psyllids in response to infected versus non-infected plants was not influenced by whether or not they were carriers of the pathogen. Quantification of volatile release from non-infected and infected plants supported the hypothesis that odorants mediate psyllid preference. Significantly more methyl salicylate, yet less methyl anthranilate and D-limonene, was released by infected than non-infected plants. Methyl salicylate was attractive to psyllids, while methyl anthranilate did not affect their behavior. Feeding on citrus by D. citri adults also induced release of methyl salicylate, suggesting that it may be a cue revealing location of conspecifics on host plants. Infected plants were characterized by lower levels of nitrogen, phosphorus, sulfur, zinc, and iron, as well as, higher levels of potassium and boron than non-infected plants. Collectively, our results suggest that host selection behavior of D. citri may be modified by bacterial infection of plants, which alters release of specific headspace volatiles and plant nutritional contents. Furthermore, we show in a laboratory setting that this apparent pathogen-mediated manipulation of vector behavior may facilitate pathogen spread. PMID:22457628

Induced release of a plant-defense volatile 'deceptively' attracts insect vectors to plants infected with a bacterial pathogen.

PubMed

Mann, Rajinder S; Ali, Jared G; Hermann, Sara L; Tiwari, Siddharth; Pelz-Stelinski, Kirsten S; Alborn, Hans T; Stelinski, Lukasz L

2012-01-01

Transmission of plant pathogens by insect vectors is a complex biological process involving interactions between the plant, insect, and pathogen. Pathogen-induced plant responses can include changes in volatile and nonvolatile secondary metabolites as well as major plant nutrients. Experiments were conducted to understand how a plant pathogenic bacterium, Candidatus Liberibacter asiaticus (Las), affects host preference behavior of its psyllid (Diaphorina citri Kuwayama) vector. D. citri were attracted to volatiles from pathogen-infected plants more than to those from non-infected counterparts. Las-infected plants were more attractive to D. citri adults than non-infected plants initially; however after feeding, psyllids subsequently dispersed to non-infected rather than infected plants as their preferred settling point. Experiments with Las-infected and non-infected plants under complete darkness yielded similar results to those recorded under light. The behavior of psyllids in response to infected versus non-infected plants was not influenced by whether or not they were carriers of the pathogen. Quantification of volatile release from non-infected and infected plants supported the hypothesis that odorants mediate psyllid preference. Significantly more methyl salicylate, yet less methyl anthranilate and D-limonene, was released by infected than non-infected plants. Methyl salicylate was attractive to psyllids, while methyl anthranilate did not affect their behavior. Feeding on citrus by D. citri adults also induced release of methyl salicylate, suggesting that it may be a cue revealing location of conspecifics on host plants. Infected plants were characterized by lower levels of nitrogen, phosphorus, sulfur, zinc, and iron, as well as, higher levels of potassium and boron than non-infected plants. Collectively, our results suggest that host selection behavior of D. citri may be modified by bacterial infection of plants, which alters release of specific headspace volatiles and plant nutritional contents. Furthermore, we show in a laboratory setting that this apparent pathogen-mediated manipulation of vector behavior may facilitate pathogen spread.

Controlling hormone signaling is a plant and pathogen challenge for growth and survival.

PubMed

López, Miguel Angel; Bannenberg, Gerard; Castresana, Carmen

2008-08-01

Plants and pathogens have continuously confronted each other during evolution in a battle for growth and survival. New advances in the field have provided fascinating insights into the mechanisms that have co-evolved to gain a competitive advantage in this battle. When plants encounter an invading pathogen, not only responses signaled by defense hormones are activated to restrict pathogen invasion, but also the modulation of additional hormone pathways is required to serve other purposes, which are equally important for plant survival, such as re-allocation of resources, control of cell death, regulation of water stress, and modification of plant architecture. Notably, pathogens can counteract both types of responses as a strategy to enhance virulence. Pathogens regulate production and signaling responses of plant hormones during infection, and also produce phytohormones themselves to modulate plant responses. These results indicate that hormone signaling is a relevant component in plant-pathogen interactions, and that the ability to dictate hormonal directionality is critical to the outcome of an interaction.

Trans-Kingdom RNA Silencing in Plant-Fungal Pathogen Interactions.

PubMed

Hua, Chenlei; Zhao, Jian-Hua; Guo, Hui-Shan

2018-02-05

Fungal pathogens represent a major group of plant invaders that are the causative agents of many notorious plant diseases. Large quantities of RNAs, especially small RNAs involved in gene silencing, have been found to transmit bidirectionally between fungal pathogens and their hosts. Although host-induced gene silencing (HIGS) technology has been developed and applied to protect crops from fungal infections, the mechanisms of RNA transmission, especially small RNAs regulating trans-kingdom RNA silencing in plant immunity, are largely unknown. In this review, we summarize and discuss recent important findings regarding trans-kingdom sRNAs and RNA silencing in plant-fungal pathogen interactions compared with the well-known RNAi mechanisms in plants and fungi. We focus on the interactions between plant and fungal pathogens with broad hosts, represented by the vascular pathogen Verticillium dahliae and non-vascular pathogen Botrytis cinerea, and discuss the known instances of natural RNAi transmission between fungal pathogens and host plants. Given that HIGS has been developed and recently applied in controlling Verticillium wilt diseases, we propose an ideal research system exploiting plant vasculature-Verticillium interaction to further study trans-kingdom RNA silencing. Copyright © 2017 The Author. Published by Elsevier Inc. All rights reserved.

Uncovering plant-pathogen crosstalk through apoplastic proteomic studies.

PubMed

Delaunois, Bertrand; Jeandet, Philippe; Clément, Christophe; Baillieul, Fabienne; Dorey, Stéphan; Cordelier, Sylvain

2014-01-01

Plant pathogens have evolved by developing different strategies to infect their host, which in turn have elaborated immune responses to counter the pathogen invasion. The apoplast, including the cell wall and extracellular space outside the plasma membrane, is one of the first compartments where pathogen-host interaction occurs. The plant cell wall is composed of a complex network of polysaccharides polymers and glycoproteins and serves as a natural physical barrier against pathogen invasion. The apoplastic fluid, circulating through the cell wall and intercellular spaces, provides a means for delivering molecules and facilitating intercellular communications. Some plant-pathogen interactions lead to plant cell wall degradation allowing pathogens to penetrate into the cells. In turn, the plant immune system recognizes microbial- or damage-associated molecular patterns (MAMPs or DAMPs) and initiates a set of basal immune responses, including the strengthening of the plant cell wall. The establishment of defense requires the regulation of a wide variety of proteins that are involved at different levels, from receptor perception of the pathogen via signaling mechanisms to the strengthening of the cell wall or degradation of the pathogen itself. A fine regulation of apoplastic proteins is therefore essential for rapid and effective pathogen perception and for maintaining cell wall integrity. This review aims to provide insight into analyses using proteomic approaches of the apoplast to highlight the modulation of the apoplastic protein patterns during pathogen infection and to unravel the key players involved in plant-pathogen interaction.

rgs-CaM Detects and Counteracts Viral RNA Silencing Suppressors in Plant Immune Priming

PubMed Central

Jeon, Eun Jin; Tadamura, Kazuki; Murakami, Taiki; Inaba, Jun-ichi; Kim, Bo Min; Sato, Masako; Atsumi, Go; Kuchitsu, Kazuyuki; Masuta, Chikara

2017-01-01

ABSTRACT Primary infection of a plant with a pathogen that causes high accumulation of salicylic acid in the plant typically via a hypersensitive response confers enhanced resistance against secondary infection with a broad spectrum of pathogens, including viruses. This phenomenon is called systemic acquired resistance (SAR), which is a plant priming for adaption to repeated biotic stress. However, the molecular mechanisms of SAR-mediated enhanced inhibition, especially of virus infection, remain unclear. Here, we show that SAR against cucumber mosaic virus (CMV) in tobacco plants (Nicotiana tabacum) involves a calmodulin-like protein, rgs-CaM. We previously reported the antiviral function of rgs-CaM, which binds to and directs degradation of viral RNA silencing suppressors (RSSs), including CMV 2b, via autophagy. We found that rgs-CaM-mediated immunity is ineffective against CMV infection in normally growing tobacco plants but is activated as a result of SAR induction via salicylic acid signaling. We then analyzed the effect of overexpression of rgs-CaM on salicylic acid signaling. Overexpressed and ectopically expressed rgs-CaM induced defense reactions, including cell death, generation of reactive oxygen species, and salicylic acid signaling. Further analysis using a combination of the salicylic acid analogue benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) and the Ca2+ ionophore A23187 revealed that rgs-CaM functions as an immune receptor that induces salicylic acid signaling by simultaneously perceiving both viral RSS and Ca2+ influx as infection cues, implying its autoactivation. Thus, secondary infection of SAR-induced tobacco plants with CMV seems to be effectively inhibited through 2b recognition and degradation by rgs-CaM, leading to reinforcement of antiviral RNA silencing and other salicylic acid-mediated antiviral responses. IMPORTANCE Even without an acquired immune system like that in vertebrates, plants show enhanced whole-plant resistance against secondary infection with pathogens; this so-called systemic acquired resistance (SAR) has been known for more than half a century and continues to be extensively studied. SAR-induced plants strongly and rapidly express a number of antibiotics and pathogenesis-related proteins targeted against secondary infection, which can account for enhanced resistance against bacterial and fungal pathogens but are not thought to control viral infection. This study showed that enhanced resistance against cucumber mosaic virus is caused by a tobacco calmodulin-like protein, rgs-CaM, which detects and counteracts the major viral virulence factor (RNA silencing suppressor) after SAR induction. rgs-CaM-mediated SAR illustrates the growth versus defense trade-off in plants, as it targets the major virulence factor only under specific biotic stress conditions, thus avoiding the cost of constitutive activation while reducing the damage from virus infection. PMID:28724770

Promiscuous Pathogenicity Islands and Phylogeny of Pathogenic Streptomyces spp.

PubMed

Zhang, Yucheng; Bignell, Dawn R D; Zuo, Ran; Fan, Qiurong; Huguet-Tapia, Jose C; Ding, Yousong; Loria, Rosemary

2016-08-01

Approximately 10 Streptomyces species cause disease on underground plant structures. The most economically important of these is potato scab, and the most studied of these pathogens is Streptomyces scabiei (syn. S. scabies). The main pathogenicity determinant of scab-causing Streptomyces species is a nitrated diketopiperazine, known as thaxtomin A (ThxA). In the pathogenic species Streptomyces turgidiscabies, ThxA biosynthetic genes reside on a mobile pathogenicity island (PAI). However, the mobilization of PAIs in other Streptomyces species remains uncharacterized. Here, we investigated the mobilization of the PAI of S. scabiei 87-22. Based on whole genome sequences, we inferred the evolutionary relationships of pathogenic Streptomyces species and discovered that Streptomyces sp. strain 96-12, a novel pathogenic species isolated from potatoes in Egypt, was phylogenetically grouped with nonpathogenic species rather than with known pathogenic species. We also found that Streptomyces sp. strain 96-12 contains a PAI that is almost identical to the PAI in S. scabiei 87-22, despite significant differences in their genome sequences. This suggested direct or indirect in vivo mobilization of the PAI between S. scabiei and nonpathogenic Streptomyces species. To test whether the S. scabiei 87-22 PAI could, indeed, be mobilized, S. scabiei 87-22 deletion mutants containing antibiotic resistance markers in the PAI were mated with Streptomyces diastatochromogenes, a nonpathogenic species. The PAI of S. scabiei was site-specifically inserted into the aviX1 gene of S. diastatochromogenes and conferred pathogenicity in radish seedling assays. Our results demonstrated that S. scabiei, the earliest described Streptomyces pathogen, could be the source of a PAI responsible for the emergence of novel pathogenic species.

Systemic Induction of the Small Antibacterial Compound in the Leaf Exudate During Benzothiadiazole-elicited Systemic Acquired Resistance in Pepper

PubMed Central

Lee, Boyoung; Park, Yong-Soon; Yi, Hwe-Su; Ryu, Choong-Min

2013-01-01

Plants protect themselves from diverse potential pathogens by induction of the immune systems such as systemic acquired resistance (SAR). Most bacterial plant pathogens thrive in the intercellular space (apoplast) of plant tissues and cause symptoms. The apoplastic leaf exudate (LE) is believed to contain nutrients to provide food resource for phytopathogenic bacteria to survive and to bring harmful phytocompounds to protect plants against bacterial pathogens. In this study, we employed the pepper-Xanthomonas axonopodis system to assess whether apoplastic fluid from LE in pepper affects the fitness of X. axonopodis during the induction of SAR. The LE was extracted from pepper leaves 7 days after soil drench-application of a chemical trigger, benzothiadiazole (BTH). Elicitation of plant immunity was confirmed by significant up-regulation of four genes, CaPR1, CaPR4, CaPR9, and CaCHI2, by BTH treatment. Bacterial fitness was evaluated by measuring growth rate during cultivation with LE from BTH- or water-treated leaves. LE from BTH-treatment significantly inhibited bacterial growth when compared to that from the water-treated control. The antibacterial activity of LE from BTH-treated samples was not affected by heating at 100°C for 30 min. Although the antibacterial molecules were not precisely identified, the data suggest that small (less than 5 kDa), heat-stable compound(s) that are present in BTH-induced LE directly attenuate bacterial growth during the elicitation of plant immunity. PMID:25288963

Pathogenic ecology: Where have all the pathogens gone? Anthrax: a classic case

NASA Astrophysics Data System (ADS)

Kiel, Johnathan; Walker, Wes W.; Andrews, Carrie J.; De Los Santos, Amy; Adams, Roy N.; Bucholz, Matthew W.; McBurnett, Shelly D.; Fuentes, Vladimir; Rizner, Karon E.; Blount, Keith W.

2009-05-01

Pathogenic ecology is the natural relationship to animate and inanimate components of the environment that support the sustainment of a pathogen in the environment or prohibit its sustainment, or their interactions with an introduced pathogen that allow for the establishment of disease in a new environment. The anthrax bacterium in the spore form has been recognized as a highly likely biological warfare or terrorist agent. The purpose of this work was to determine the environmental reservoir of Bacillus anthracis between outbreaks of anthrax and to examine the potential factors influencing the conversion of the Bacillus anthracis from a quiescent state to the disease causing state. Here we provide environmental and laboratory data for the cycling of Bacillus anthracis in plants to reconcile observations that contradict the soil borne hypothesis of anthrax maintenance in the environment.

Harnessing Host-Vector Microbiome for Sustainable Plant Disease Management of Phloem-Limited Bacteria.

PubMed

Trivedi, Pankaj; Trivedi, Chanda; Grinyer, Jasmine; Anderson, Ian C; Singh, Brajesh K

2016-01-01

Plant health and productivity is strongly influenced by their intimate interaction with deleterious and beneficial organisms, including microbes, and insects. Of the various plant diseases, insect-vectored diseases are of particular interest, including those caused by obligate parasites affecting plant phloem such as Candidatus ( Ca .) Phytoplasma species and several species of Ca. Liberibacter. Recent studies on plant-microbe and plant-insect interactions of these pathogens have demonstrated that plant-microbe-insect interactions have far reaching consequences for the functioning and evolution of the organisms involved. These interactions take place within complex pathosystems and are shaped by a myriad of biotic and abiotic factors. However, our current understanding of these processes and their implications for the establishment and spread of insect-borne diseases remains limited. This article highlights the molecular, ecological, and evolutionary aspects of interactions among insects, plants, and their associated microbial communities with a focus on insect vectored and phloem-limited pathogens belonging to Ca. Phytoplasma and Ca. Liberibacter species. We propose that innovative and interdisciplinary research aimed at linking scales from the cellular to the community level will be vital for increasing our understanding of the mechanisms underpinning plant-insect-microbe interactions. Examination of such interactions could lead us to applied solutions for sustainable disease and pest management.

Freeze-fracture of infected plant leaves in ethanol for scanning electron microscopic study of fungal pathogens.

PubMed

Moore, Jayma A; Payne, Scott A

2012-01-01

Fungi often are found within plant tissues where they cannot be visualized with the scanning electron microscope (SEM). We present a simple way to reveal cell interiors while avoiding many common causes of artifact. Freeze-fracture of leaf tissue using liquid nitrogen during the 100% ethanol step of the dehydration process just before critical point drying is useful in exposing intracellular fungi to the SEM.

Protection against common bean rust conferred by a gene silencing method

USDA-ARS?s Scientific Manuscript database

Rust disease of the dry bean plant, Phaseolus vulgaris, is caused by the fungus Uromyces appendiculatus. The fungus acquires its nutrients and energy from bean leaves using a specialized cell structure, the haustorium, through which it secretes effector proteins that contribute to pathogenicity by ...

Plant Natural Compounds with Antibacterial Activity Towards Common Pathogens of Pond-Cultured Channel Catfish (Ictalurus punctatus)

USDA-ARS?s Scientific Manuscript database

The bacteria Edwardsiella ictaluri and Flavobacterium columnare cause enteric septicemia and columnaris disease, respectively, in channel catfish (Ictalurus punctatus). Natural therapeutants may provide an alternative to current management approaches used by producers. In this study, a rapid bioas...

Pre-Breeding for root rot resistance using root morphology traits

USDA-ARS?s Scientific Manuscript database

Root rot caused by the fungal pathogen Rhizoctonia solani can be a major yield-limiting disease in minimal tillage or direct-seeded cereal production systems. Reduced tillage greatly influences the plant residue retained on the soil surfaces. This retained residue (green bridge) provides increased d...

Identification of candidate effector genes of Pratylenchus penetrans

USDA-ARS?s Scientific Manuscript database

Pratylenchus penetrans is considered one of the most important species among root lesion nematodes (RLN) due to the detrimental and economic impact that it causes in a wide range of crops. Similar to other plant-pathogens, P. penetrans harbors a significant number of predicted secreted proteins that...

Spinach downy mildew – Threat, prevention and control

USDA-ARS?s Scientific Manuscript database

Downy mildew disease is a widespread and destructive disease of spinach in California and elsewhere where spinach is grown, and is caused by Peronospora effusa, an obligate, plant pathogenic oomycete. As in the case with most other crops damaged by downy mildews, spinach downy mildew culminates in ...