Host-Specific Toxins of Alternaria Plant Pathogens and Molecular Mechanisms of Host Specificity.

To develop efficient biocontrol agents, it is essential to investigate the response of soil-borne plant pathogens to such agents. For example, the response of Ralstonia solanacearum, the tomato wilt pathogen, to antimicrobial metabolites of Pseudomonas fluorescens is unknown. Thus, we assessed the effects of P. fluorescens SN15-2 fermentation broth on R. solanacearum by transmission electron microscopy and transcriptome technology. RNA sequencing identified 109 and 155 genes that are significantly upregulated and downregulated, respectively, in response to P. fluorescens metabolites, many of which are associated with the cell membrane and cell wall, and with nucleotide acid metabolism, iron absorption, and response to oxidative stress. This study highlights the effectiveness of P. fluorescens metabolites against the tomato wilt pathogen and helps clarify the underlying molecular mechanisms.

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The actin cytoskeleton mediates transmission of Candidatus Liberibacter solanacearum by the carrot psyllid

Applied and Environmental Microbiology ◽

10.1128/aem.02393-20 ◽

2020 ◽

Author(s):

Poulami Sarkar ◽

Svetlana Kontsedalov ◽

Galina Lebedev ◽

Murad Ghanim

Keyword(s):

Actin Cytoskeleton ◽

Defense Mechanisms ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Plant Diseases ◽

Citrus Industry ◽

Citrus Greening Disease ◽

Associated Diseases ◽

Novel Approach ◽

Vector Borne

Several vector-borne plant pathogens have evolved mechanisms to exploit and hijack vector host cellular, molecular and defense mechanisms for their transmission. Over the past few years, Liberibacter species, which are transmitted by several psyllid vectors, have become an economically important group of pathogens that devastated the citrus industry and caused tremendous losses to many other important crops worldwide. The molecular mechanisms underlying the interactions of Liberibacter species with their psyllid vectors are poorly studied. Candidatus Liberibacter solanacearum (CLso) associated with important vegetable diseases is transmitted by the carrot psyllid, Bactericera trigonica in a persistent manner. Here, we elucidated the role of B. trigonica Arp2/3 protein complex, which plays a major role in the regulation of the actin cytoskeleton, in the transmission of CLso. CLso co-localized with ArpC2, a key protein in this complex, and this co-localization strongly associated with actin filaments. Silencing the psyllid ArpC2 disrupted the co-localization and the dynamics of F-actin. Silencing RhoGAP21 and Cdc42, which act in the signaling cascade leading to upregulation of Arp2/3 and F-actin bundling, also showed similar results. On the other hand, silencing ArpC5, another component of the complex, did not induce any significant effects on F-actin formation. Finally, ArpC2 silencing caused 73.4% reduction in CLso transmission by psyllids, strongly suggesting that its transmission by B. trigonica is cytoskeleton-dependent and it interacts with ArpC2 to exploit the intracellular actin nucleation process for transmission. Targeting this unique interaction could lead to developing a novel strategy for the management of Liberibacter-associated diseases. IMPORTANCE Plant diseases caused by vector-borne pathogens are responsible for tremendous losses and threaten some of the most important agricultural crops. A good example is the citrus greening disease caused by bacteria of the genus Liberibacter and transmitted by psyllids, and has devastated the citrus industry in the US, China and Brazil. Here we show that the psyllid-transmitted Candidatus Liberibacter solanacearum (CLso) employs the actin cytoskeleton of psyllid gut cells, specifically the ArpC2 protein in the Arp2/3 complex of this system, for movement and transmission in the vector. Silencing ArpC2 dramatically influenced interaction of CLso with the cytoskeleton and decreased the bacteria transmission to plants. This system could be targeted for developing a novel approach for the control of Liberibacter- associated diseases.

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‘Candidatus Phytoplasma solani’ interferes with the distribution and uptake of iron in tomato

BMC Genomics ◽

10.1186/s12864-019-6062-x ◽

2019 ◽

Vol 20 (1) ◽

Cited By ~ 4

Author(s):

Sara Buoso ◽

Laura Pagliari ◽

Rita Musetti ◽

Marta Martini ◽

Fabio Marroni ◽

...

Keyword(s):

Plant Pathogens ◽

Molecular Mechanisms ◽

Transcriptional Response ◽

Transcriptome Profiling ◽

Transport Processes ◽

Fe Deficiency ◽

Cultivated Plants ◽

Chlorophyll Metabolism ◽

Wide Range ◽

Phytoplasma Infection

Abstract Background ‘Candidatus Phytoplasma solani’ is endemic in Europe and infects a wide range of weeds and cultivated plants. Phytoplasmas are prokaryotic plant pathogens that colonize the sieve elements of their host plant, causing severe alterations in phloem function and impairment of assimilate translocation. Typical symptoms of infected plants include yellowing of leaves or shoots, leaf curling, and general stunting, but the molecular mechanisms underlying most of the reported changes remain largely enigmatic. To infer a possible involvement of Fe in the host-phytoplasma interaction, we investigated the effects of ‘Candidatus Phytoplasma solani’ infection on tomato plants (Solanum lycopersicum cv. Micro-Tom) grown under different Fe regimes. Results Both phytoplasma infection and Fe starvation led to the development of chlorotic leaves and altered thylakoid organization. In infected plants, Fe accumulated in phloem tissue, altering the local distribution of Fe. In infected plants, Fe starvation had additive effects on chlorophyll content and leaf chlorosis, suggesting that the two conditions affected the phenotypic readout via separate routes. To gain insights into the transcriptional response to phytoplasma infection, or Fe deficiency, transcriptome profiling was performed on midrib-enriched leaves. RNA-seq analysis revealed that both stress conditions altered the expression of a large (> 800) subset of common genes involved in photosynthetic light reactions, porphyrin / chlorophyll metabolism, and in flowering control. In Fe-deficient plants, phytoplasma infection perturbed the Fe deficiency response in roots, possibly by interference with the synthesis or transport of a promotive signal transmitted from the leaves to the roots. Conclusions ‘Candidatus Phytoplasma solani’ infection changes the Fe distribution in tomato leaves, affects the photosynthetic machinery and perturbs the orchestration of root-mediated transport processes by compromising shoot-to-root communication.

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The mirid bug Apolygus lucorum deploys a glutathione peroxidase as a candidate effector to enhance plant susceptibility

Journal of Experimental Botany ◽

10.1093/jxb/eraa015 ◽

2020 ◽

Vol 71 (9) ◽

pp. 2701-2712

Author(s):

Yumei Dong ◽

Maofeng Jing ◽

Danyu Shen ◽

Chenyang Wang ◽

Meiqian Zhang ◽

...

Keyword(s):

Cell Death ◽

Salivary Gland ◽

Glutathione Peroxidase ◽

Large Scale ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Mechanism Analysis ◽

Apolygus Lucorum ◽

Mirid Bug ◽

Plant Susceptibility

Abstract The mirid bug Apolygus lucorum has become a major agricultural pest since the large-scale cultivation of Bt-cotton. It was assumed that A. lucorum, similarly to other phloem sap insects, could secrete saliva that contains effector proteins into plant interfaces to perturb host cellular processes during feeding. However, the secreted effectors of A. lucorum are still uncharacterized and unstudied. In this study, 1878 putative secreted proteins were identified from the transcriptome of A. lucorum, which either had homology with published aphid effectors or shared common features with plant pathogens and insect effectors. One hundred and seventy-two candidate effectors were used for cell death-inducing/suppressing assays, and a putative salivary gland effector, Apolygus lucorum cell death inhibitor 6 (Al6), was characterized. The mRNAs of Al6 were enriched at feeding stages (nymph and adult) and, in particular, in salivary glands. Moreover, we revealed that the secreted Al6 encoded an active glutathione peroxidase that reduced reactive oxygen species (ROS) accumulation induced by INF1 or Flg22. Expression of the Al6 gene in planta altered insect feeding behavior and promoted plant pathogen infections. Inhibition of cell death and enhanced plant susceptibility to insect and pathogens are dependent on glutathione peroxidase activity of Al6. Thus, this study shows that a candidate salivary gland effector, Al6, functions as a glutathione peroxidase and suppresses ROS induced by pathogen-associated molecular pattern to inhibit pattern-triggered immunity (PTI)-induced cell death. The identification and molecular mechanism analysis of the Al6 candidate effector in A. lucorum will provide new insight into the molecular mechanisms of insect–plant interactions.

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Molecular karyotypes for Alternaria plant pathogens known to produce host-specific toxins

Current Genetics ◽

10.1007/s002940050464 ◽

1999 ◽

Vol 35 (6) ◽

pp. 647-656 ◽

Cited By ~ 90

Author(s):

Hajime Akamatsu ◽

Masatoki Taga ◽

M. Kodama ◽

Richard Johnson ◽

Hiroshi Otani ◽

...

Keyword(s):

Plant Pathogens ◽

Host Specific Toxins

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The bunyavirus nonstructural protein NSs suppresses plant immunity to facilitate its own transmission by improving vector insect performance

10.1101/424143 ◽

2018 ◽

Author(s):

Xiujuan Wu ◽

Shuang Xu ◽

Pingzhi Zhao ◽

Xiangmei Yao ◽

Yanwei Sun ◽

...

Keyword(s):

Molecular Mechanism ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Nonstructural Protein ◽

Pathogen Transmission ◽

Terpene Synthase ◽

Silencing Suppressor ◽

Suppressor Activity ◽

Arthropod Vectors ◽

Vector Behavior

AbstractPandemics of vector-borne human and plant pathogens often rely on the behaviors of their arthropod vectors. Arboviruses, including many bunyaviruses, manipulate vector behavior to accelerate their own transmission to vertebrates, birds, insects, and plants. However, the molecular mechanism underlying this manipulation remains elusive. Here, we report that the non-structural protein NSs of orthotospovirus (order Bunyavirales, family Tospoviridae), is a key viral factor that indirectly modifies vector preference and increases vector performance. NSs suppresses the biosynthesis of volatile monoterpenes, which serve as repellents of the vector Western flower thrips (WFT, Frankliniella occidentalis) instead of using its known silencing suppressor activity. NSs directly interacts with and relocalizes the jasmonate (JA) signaling master regulator MYC2 and its two close homologs, MYC3 and MYC4, to disable JA-mediated activation of terpene synthase genes. The dysfunction of the MYCs subsequently attenuates host defenses, increases the attraction of thrips, and improves thrips fitness. These findings elucidate the molecular mechanism through which a bunyavirus manipulates vector behaviors and therefore facilitate disease transmission. Our results provide important insights into the molecular mechanisms by which tospoviruses NSs counteracts host immunity for pathogen transmission.Author summaryMost bunyaviruses are transmitted by insect vectors, and some of them can modify the behaviors of their arthropod vectors to increase transmission to mammals, birds, and plants. NSs is a non-structural bunyavirus protein with multiple functions that acts as an avirulence determinant and silencing suppressor. In this study, we identified a new function of NSs as a manipulator of vector behavior, independent of its silencing suppressor activity. NSs manipulates jasmonate-mediated immunity against thrips by directly interacting with several homologs of MYC transcription factors, the core regulators of the jasmonate-signaling pathway. This hijacking by NSs enhances thrips preference and performance. Many human- and animal-infecting members of the Bunyaviridales also encode NSs and could manipulate vector behavior to accelerate their own transmission. Therefore, our data support the hypothesis that the NSs protein may play conserved roles among various members of the Bunyaviridales in the modification of vector feeding behavior that evolved as a mechanism to enhance virus transmission.

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Host targets of effectors of the lettuce downy mildew Bremia lactucae from cDNA-based yeast two-hybrid screening

10.1101/863738 ◽

2019 ◽

Author(s):

Alexandra J.E. Pelgrom ◽

Claudia-Nicole Meisrimler ◽

Joyce Elberse ◽

Thijs Koorman ◽

Mike Boxem ◽

...

Keyword(s):

Downy Mildew ◽

Pathogenic Bacteria ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Effector Proteins ◽

Bremia Lactucae ◽

Yeast Two Hybrid ◽

Target Proteins ◽

Successful Infection ◽

Two Hybrid

AbstractPlant pathogenic bacteria, fungi and oomycetes secrete effector proteins to manipulate host cell processes to establish a successful infection. Over the last decade the genomes and transcriptomes of many agriculturally important plant pathogens have been sequenced and vast candidate effector repertoires were identified using bioinformatic analyses. Elucidating the contribution of individual effectors to pathogenicity is the next major hurdle. To advance our understanding of the molecular mechanisms underlying lettuce susceptibility to the downy mildew Bremia lactucae, we mapped a network of physical interactions between B. lactucae effectors and lettuce target proteins. Using a lettuce cDNA library-based yeast-two-hybrid system, 61 protein-protein interactions were identified, involving 21 B. lactucae effectors and 46 unique lettuce proteins. The top ten targets based on the number of independent colonies identified in the Y2H and two targets that belong to gene families involved in plant immunity, were further characterized. We determined the subcellular localization of the fluorescently tagged target proteins and their interacting effectors. Importantly, relocalization of effectors or targets to the nucleus was observed for four effector-target pairs upon their co-expression, supporting their interaction in planta.

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Molecular mechanisms of host cell manipulation by plant pathogens

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273314091980 ◽

2014 ◽

Vol 70 (a1) ◽

pp. C801-C801

Author(s):

Richard Hughes ◽

Stuart King ◽

Abbas Maqbool ◽

Hazel McLellan ◽

Tolga Bozkurt ◽

...

Keyword(s):

Cell Death ◽

Crop Production ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Complex Structure ◽

Effector Proteins ◽

Plant Diseases ◽

Cell Manipulation ◽

Cell Physiology ◽

Structural Studies

An estimated 15% of global crop production is lost to pre-harvest disease every year. New ways to manage plant diseases are required. A mechanistic understanding of how plant pathogens re-program their hosts to enable colonisation may provide novel genetic or chemical opportunities to interfere with disease. One notorious plant parasite is the Irish potato famine pathogen Phytophthora infestans. This pathogen remains a considerable threat to potato/tomato crops today as the agent of late blight. Plant pathogens secrete effector proteins outside of and into plant cells to suppress host defences and manipulate cell physiology. Structural studies have provided insights into effector evolution and enabled experiments to probe function [1-3]. Crystal structures of 4 Phytophthora RXLR-type effectors, which are unrelated in primary sequence, revealed similarities in the fold of these proteins. This fold was proposed to act as a stable scaffold that supports diversification of effectors. Further, molecular modelling has enabled mapping of single-site variants responsible for specialisation of a Phytophthora Cystatin-like effector, revealing how effectors can adapt to new hosts after a "host jump". Structural studies describing how RXLR-effectors interact with host targets are lacking. We have used Y2H/co-IP studies to identify host proteins that interact with P. infestans effectors PexRD2 and PexRD54. PexRD2 interacts with MAPKKKe, a component of plant immune signalling pathways, and suppressed cell death activities of this protein. We used the structure of PexRD2 to design mutants that fail to interact with MAPKKKe, and no longer suppress cell-death activities. We found that PexRD54 interacts with potato homologues of the autophagy protein ATG8. We have obtained a crystal structure for PexRD54 in the presence of ATG8. We are now using X-ray scattering to verify the complex structure in solution prior to establishing the role of this interaction during infection.

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Comparative analyses of saprotrophy in Salisapilia sapeloensis and diverse plant pathogenic oomycetes reveal lifestyle-specific gene expression

FEMS Microbiology Ecology ◽

10.1093/femsec/fiaa184 ◽

2020 ◽

Vol 96 (11) ◽

Author(s):

Sophie de Vries ◽

Jan de Vries ◽

John M Archibald ◽

Claudio H Slamovits

Keyword(s):

Gene Expression ◽

Regulatory Networks ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Expression Patterns ◽

Reference Points ◽

Global Perspective ◽

Specific Gene ◽

Gene Regulatory ◽

Specific Array

ABSTRACT Oomycetes include many devastating plant pathogens. Across oomycete diversity, plant-infecting lineages are interspersed by non-pathogenic ones. Unfortunately, our understanding of the evolution of lifestyle switches is hampered by a scarcity of data on the molecular biology of saprotrophic oomycetes, ecologically important primary colonizers of dead tissue that can serve as informative reference points for understanding the evolution of pathogens. Here, we established Salisapilia sapeloensis as a tractable system for the study of saprotrophic oomycetes. We generated multiple transcriptomes from S. sapeloensis and compared them with (i) 22 oomycete genomes and (ii) the transcriptomes of eight pathogenic oomycetes grown under 13 conditions. We obtained a global perspective on gene expression signatures of oomycete lifestyles. Our data reveal that oomycete saprotrophs and pathogens use similar molecular mechanisms for colonization but exhibit distinct expression patterns. We identify a S. sapeloensis-specific array and expression of carbohydrate-active enzymes and putative regulatory differences, highlighted by distinct expression levels of transcription factors. Salisapilia sapeloensis expresses only a small repertoire of candidates for virulence-associated genes. Our analyses suggest lifestyle-specific gene regulatory signatures and that, in addition to variation in gene content, shifts in gene regulatory networks underpin the evolution of oomycete lifestyles.

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The CC domain structure from the wheat stem rust resistance protein Sr33 challenges paradigms for dimerization in plant NLR proteins

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1609922113 ◽

2016 ◽

Vol 113 (45) ◽

pp. 12856-12861 ◽

Cited By ~ 54

Author(s):

Lachlan W. Casey ◽

Peter Lavrencic ◽

Adam R. Bentham ◽

Stella Cesari ◽

Daniel J. Ericsson ◽

...

Keyword(s):

Cell Death ◽

Stem Rust ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Structural Basis ◽

Wheat Stem Rust ◽

Pathogen Effector ◽

Resistance Protein ◽

Cell Death Signaling ◽

Self Association

Plants use intracellular immunity receptors, known as nucleotide-binding oligomerization domain-like receptors (NLRs), to recognize specific pathogen effector proteins and induce immune responses. These proteins provide resistance to many of the world’s most destructive plant pathogens, yet we have a limited understanding of the molecular mechanisms that lead to defense signaling. We examined the wheat NLR protein, Sr33, which is responsible for strain-specific resistance to the wheat stem rust pathogen, Puccinia graminis f. sp. tritici. We present the solution structure of a coiled-coil (CC) fragment from Sr33, which adopts a four-helix bundle conformation. Unexpectedly, this structure differs from the published dimeric crystal structure of the equivalent region from the orthologous barley powdery mildew resistance protein, MLA10, but is similar to the structure of the distantly related potato NLR protein, Rx. We demonstrate that these regions are, in fact, largely monomeric and adopt similar folds in solution in all three proteins, suggesting that the CC domains from plant NLRs adopt a conserved fold. However, larger C-terminal fragments of Sr33 and MLA10 can self-associate both in vitro and in planta, and this self-association correlates with their cell death signaling activity. The minimal region of the CC domain required for both cell death signaling and self-association extends to amino acid 142, thus including 22 residues absent from previous biochemical and structural protein studies. These data suggest that self-association of the minimal CC domain is necessary for signaling but is likely to involve a different structural basis than previously suggested by the MLA10 crystallographic dimer.

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