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The biotroph Agrobacterium tumefaciens thrives in tumors by exploiting a wide spectrum of plant host metabolites - Gonzalez‐Mula - - New Phytologist - Wiley Online Library

TnSeq + RNAseq on Agrobacterium tumefaciens (D. Faure - 2018)
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Clubroot Disease Stimulates Early Steps of Phloem Differentiation and Recruits SWEET Sucrose Transporters within Developing Galls

Clubroot Disease Stimulates Early Steps of Phloem Differentiation and Recruits SWEET Sucrose Transporters within Developing Galls | Xanthomonas | Scoop.it
Successful biotrophic plant pathogens can divert host nutrition towards infection sites. Here we describe how the protist Plasmodiophora brassicae establishes a long-term feeding relationship with its host by stimulating phloem differentiation and phloem-specific expression of sugar transporters within developing galls. Development of galls in infected Arabidopsis thaliana plants is accompanied by stimulation of host BREVIS RADIX (BRX), COTYLEDON VASCULAR PATTERN 2 (CVP2) and OCTOPUS (OPS) gene expression leading to an increase in phloem complexity. We characterised how the arrest of this developmental reprogramming influences both the host and the invading pathogen. Furthermore, we found that infection leads to phloem-specific accumulation of SUGARS WILL EVENTUALLY BE EXPORTED TRANSPORTERS (SWEET11 and SWEET12) facilitating local distribution of sugars towards the pathogen. Utilising Fourier-transform infrared (FTIR) microspectroscopy to monitor spatial distribution of carbohydrates, we found that infection leads to the formation of a strong physiological sink at the site of infection. High resolution metabolic and structural imaging of sucrose distributions revealed that sweet11 sweet12 double mutants are impaired in sugar transport towards the pathogen, delaying disease progression. This work highlights the importance of precise regulation of sugar partitioning for plant-pathogen interactions and the dependence of P. brassicae's performance on its capacity to induce a phloem sink at the feeding site.
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Molecular mimicry modulates plant host responses to pathogens | Annals of Botany | Oxford Academic

Molecular mimicry modulates plant host responses to pathogens | Annals of Botany | Oxford Academic | Xanthomonas | Scoop.it

Pamela Ronald & Anna Joe, 2018


Pathogens often secrete molecules that mimic those present in the plant host. Recent studies indicate that some of these molecules mimic plant hormones required for development and immunity.

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Visualization of the type III secretion mediated Salmonella–host cell interface using cryo-electron tomography

Visualization of the type III secretion mediated Salmonella–host cell interface using cryo-electron tomography | Xanthomonas | Scoop.it
Donghyun Park, Maria Lara-Tejero, M Neal Waxham, Wenwei Li, Bo Hu, Jorge E Galán, Jun Liu
Many important gram-negative bacterial pathogens use highly sophisticated type III protein secretion systems (T3SSs) to establish complex host-pathogen interactions. Bacterial-host cell contact triggers the activation of the T3SS and the subsequent insertion of a translocon pore into the target cell membrane, which serves as a conduit for the passage of effector proteins. Therefore the initial interaction between T3SS-bearing bacteria and host cells is the critical step in the deployment of the protein secretion machine, yet this process remains poorly understood. Here, we use high-throughput cryo-electron tomography (cryo-ET) to visualize the T3SS-mediated Salmonella-host cell interface. Our analysis reveals the intact translocon at an unprecedented level of resolution, its deployment in the host cell membrane, and the establishment of an intimate association between the bacteria and the target cells, which is essential for effector translocation. Our studies provide critical data supporting the long postulated direct injection model for effector translocation.


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Identification by Tn‐seq of Dickeya dadantii genes required for survival in chicory plants

Identification by Tn‐seq of Dickeya dadantii genes required for survival in chicory plants | Xanthomonas | Scoop.it
Kévin Royet, Nicolas Parisot, Agnès Rodrigue, Erwan Gueguen, Guy Condemine

Identification of the virulence factors of plant pathogenic bacteria has relied on the test of individual mutants on plants, a time‐consuming process. Tn‐seq is a very powerful method for identifying those genes required for bacterial growth in their host. We used this method in a soft‐rot pathogenic bacterium to identify the genes required for the multiplication of Dickeya dadantii in chicory. About 100 genes were identified showing decreased or increased fitness in the plant. Most of them had no previously attributed role in plant‐bacteria interaction. Following our screening, in planta competition assays confirmed that the uridine monophosphate biosynthesis pathway and the purine biosynthesis pathway are essential to the survival of Dickeya dadantii in the plant since the mutants ∆carA, ∆purF, ∆purL, ∆guaB and ∆pyrE are unable to survive in the plant in contrast to the WT bacterium. This study also demonstrates that the biosynthetic pathways of leucine, cysteine and lysine are essential for bacterial survival in the plant and that RsmC and GcpA are important in regulating the infection process since the mutants ∆rsmC and ∆gcpA are hypervirulent. Finally, our study shows that D. dadantii flagellin is glycosylated and that this modification confers fitness to the bacteria during plant infection. Assay by this method of large collections of environmental pathogenic strains now available will allow an easy and rapid identification of new virulence factors.

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Role of the acquisition of a Type 3 Secretion System in the emergence of novel pathogenic strains of Xanthomonas

Cases of emergence of novel plant pathogenic strains are regularly reported that hinder yield of crops and trees. However the molecular mechanisms underlying such emergence are still poorly understood. The acquisition by environmental non‐pathogenic strains of novel virulence genes by horizontal gene transfer has been suggested as a driver for the emergence of novel pathogenic strains. In the present study, we tested such an hypothesis by transferring a plasmid encoding the Type 3 Secretion System (T3SS) and four associated Type 3 Secreted proteins (T3SPs) to the non‐pathogenic strains of Xanthomonas CFBP 7698 and CFBP 7700, that lack genes encoding T3SS and any previously known T3SPs. The resulting strains were phenotyped on Nicotiana benthamiana using chlorophyll fluorescence imaging and image analysis. Wild‐type non‐pathogenic strains induced a HR‐like necrosis, while strains complemented with the T3SS and T3SPs suppressed it. Such suppression depends on a functional T3SS. Among the T3SPs encoded on the plasmid, Hpa2, Hpa1, and to a lesser extend XopF1, collectively participate to the suppression. Monitoring the population sizes in planta showed that the sole acquisition of a functional T3SS by non‐pathogenic strains impairs growth inside leaf tissues. These results provide functional evidence that the acquisition via horizontal gene transfer of a T3SS and four T3SPs by environmental non‐pathogenic strains is not sufficient to make strains pathogenic. In the absence of canonical effector, the sole acquisition of a T3SS seems counter‐selected, and further acquisition of type 3 effectors is probably needed to allow the emergence of novel pathogenic strains.
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Bodyguards: Pathogen-Derived Decoys That Protect Virulence Factors

Bodyguards: Pathogen-Derived Decoys That Protect Virulence Factors | Xanthomonas | Scoop.it
Model of Two Bodyguards at Work. (A) Effector decoy XLP1 prevents host protein GIP1 from inhibiting glucanase XEG1. (B) Truncated TALEs prevent TALE effectors from being recognized by immune receptors Xa1/Xo1. Abbreviations: ETI, effector-triggered immunity; GIP1, glucanase inhibitor protein; TALE, Transcription activator-like effectors; Xa1, R gene in rice; XEG1, Xyloglucanase; XLP1, XEG1-Like Protein; ​Xo1, R gene in rice.

Recent studies on plant-pathogen interactions have exposed a new strategy used by plant pathogens: decoy effectors that protect virulence factors. Examples of these “bodyguards” include the recently discovered PsXLP1 from Phytophthora sojae and truncated TALEs from Xanthomonas oryzae. These examples suggest important roles for seemingly non-functional effector proteins in distracting the host.
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Bacterial adhesion at the single-cell level

Bacterial adhesion at the single-cell level | Xanthomonas | Scoop.it

Cecile Berne, Courtney K. Ellison, Adrien Ducret and Yves V. Brun 


In this Review, Brun and colleagues summarize our understanding of the mechanisms governing bacterial adhesion at the single-cell level, including the physical forces experienced by a cell before reaching the surface, the first contact with a surface and the transition from reversible to permanent adhesion.

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Receptor networks underpin plant immunity

Receptor networks underpin plant immunity | Xanthomonas | Scoop.it

Chih-Hang Wu, Lida Derevnina and Sophien Kamoun


Plants are attacked by a multitude of pathogens and pests, some of which cause epidemics that threaten food security. Yet a fundamental concept in plant pathology is that most plants are actively resistant to most pathogens and pests. Plants fend off their innumerable biotic foes primarily through innate immune receptors that detect the invading pathogens and trigger a robust immune response. The conceptual basis of such interactions was elegantly articulated by Harold H. Flor, who, in 1942, proposed the hypothesis that single genes in plants and pathogens define the outcome of their interactions; that is, a plant harboring a specific gene displays resistance against a pathogen that carries an interacting virulence gene ( 1 ). This gene-for-gene model was hugely insightful and influential—it has helped to guide applied and basic research on disease resistance. However, recent findings are taking the field beyond this simplified binary view of plant-pathogen interactions. Plants carry extremely diverse and dynamic repertoires of immune receptors that are interconnected in complex ways. Conversely, plant pathogens secrete a diversity of virulence proteins and metabolites called effectors, and pathogen genomics has revealed hundreds of effector genes in many species. These effectors have evidently evolved to favor pathogen infection and spread, but a subset of them inadvertently activate plant immune receptors. The emerging paradigm is that dynamic webs of genetic and biochemical networks underpin the early stages of plant-pathogen interactions.

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Xylella fastidiosa: an examination of a re‐emerging plant pathogen

Xylella fastidiosa: an examination of a re‐emerging plant pathogen | Xanthomonas | Scoop.it
JEANNETTE RAPICAVOLI, BRIAN INGEL, BARBARA BLANCO-ULATE, DARIO CANTU AND CAROLINE ROPER (2018)

SUMMARY: Xylella fastidiosa is a Gram-negative bacterialplant pathogen with an extremely wide host range. This specieshas recently been resolved into subspecies that correlate withhost specificity. This review focuses on the status of X. fastidiosapathogenic associations in plant hosts in which the bacterium iseither endemic or has been recently introduced. Plant diseasesassociated with X. fastidiosa have been documented for over acentury, and much about what is known in the context of host–pathogen interactions is based on these hosts, such as grape andcitrus, in which this pathogen has been well described. Recentattention has focused on newly emerging X. fastidiosa diseases,such as in olives.
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Functional analysis of African Xanthomonas oryzae pv. oryzae TALomes reveals a new susceptibility gene in bacterial leaf blight of rice

Functional analysis of African Xanthomonas oryzae pv. oryzae TALomes reveals a new susceptibility gene in bacterial leaf blight of rice | Xanthomonas | Scoop.it
Tuan T. Tran , Alvaro L. Pérez-Quintero , Issa Wonni, Sara C. D. Carpenter, Yanhua Yu, Li Wang, Jan E. Leach, Valérie Verdier, Sébastien Cunnac, Adam J. Bogdanove, Ralf Koebnik, Mathilde Hutin, Boris Szurek

Most Xanthomonas species translocate Transcription Activator-Like (TAL) effectors into plant cells where they function like plant transcription factors via a programmable DNA-binding domain. Characterized strains of rice pathogenic X. oryzae pv. oryzae harbor 9–16 different tal effector genes, but the function of only a few of them has been decoded. Using sequencing of entire genomes, we first performed comparative analyses of the complete repertoires of TAL effectors, herein referred to as TALomes, in three Xoo strains forming an African genetic lineage different from Asian Xoo. A phylogenetic analysis of the three TALomes combined with in silico predictions of TAL effector targets showed that African Xoo TALomes are highly conserved, genetically distant from Asian ones, and closely related to TAL effectors from the bacterial leaf streak pathogen Xanthomonas oryzae pv. oryzicola (Xoc). Nine clusters of TAL effectors could be identified among the three TALomes, including three showing higher levels of variation in their repeat variable diresidues (RVDs). Detailed analyses of these groups revealed recombination events as a possible source of variation among TAL effector genes. Next, to address contribution to virulence, nine TAL effector genes from the Malian Xoo strain MAI1 and four allelic variants from the Burkinabe Xoo strain BAI3, thus representing most of the TAL effector diversity in African Xoo strains, were expressed in the TAL effector-deficient X. oryzae strain X11-5A for gain-of-function assays. Inoculation of the susceptible rice variety Azucena lead to the discovery of three TAL effectors promoting virulence, including two TAL effectors previously reported to target the susceptibility (S) gene OsSWEET14 and a novel major virulence contributor, TalB. RNA profiling experiments in rice and in silico prediction of EBEs were carried out to identify candidate targets of TalB, revealing OsTFX1, a bZIP transcription factor previously identified as a bacterial blight S gene, and OsERF#123, which encodes a subgroup IXc AP2/ERF transcription factor. Use of designer TAL effectors demonstrated that induction of either gene resulted in greater susceptibility to strain X11-5A. The induction of OsERF#123 by BAI3Δ1, a talB knockout derivative of BAI3, carrying these designer TAL effectors increased virulence of BAI3Δ1, validating OsERF#123 as a new, bacterial blight S gene.
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Defining essential processes in plant pathogenesis with Pseudomonas syringae pv. tomato DC3000 disarmed polymutants and a subset of key type III effectors

Defining essential processes in plant pathogenesis with Pseudomonas syringae pv. tomato DC3000 disarmed polymutants and a subset of key type III effectors | Xanthomonas | Scoop.it
Hai‐Lei Wei and Alan Collmer

Pseudomonas syringae pv. tomato DC3000 and its derivatives cause disease in tomato, Arabidopsis and Nicotiana benthamiana. The primary virulence factors include a repertoire of 29 effector proteins injected into plant cells by the type III secretion system and the phytotoxin coronatine. The complete repertoire of effector genes and key coronatine biosynthesis genes have been progressively deleted and minimally reassembled to reconstitute basic pathogenic ability in N. benthamiana, and in Arabidopsis plants that have mutations in target genes that mimic effector actions. This approach and molecular studies of effector activities and plant immune system targets have highlighted a small subset of effectors that contribute to essential processes in pathogenesis. Most notably, HopM1 and AvrE1 redundantly promote an aqueous apoplastic environment, and AvrPtoB and AvrPto redundantly block early immune responses, two conditions that are sufficient for substantial bacterial growth in planta. In addition, disarmed DC3000 polymutants have been used to identify the individual effectors responsible for specific activities of the complete repertoire and to more effectively study effector domains, effector interplay and effector actions on host targets. Such work has revealed that AvrPtoB suppresses cell death elicitation in N. benthamiana that is triggered by another effector in the DC3000 repertoire, highlighting an important aspect of effector interplay in native repertoires. Disarmed DC3000 polymutants support the natural delivery of test effectors and infection readouts that more accurately reveal effector functions in key pathogenesis processes, and enable the identification of effectors with similar activities from a broad range of other pathogens that also defeat plants with cytoplasmic effectors.
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Mutant phenotypes for thousands of bacterial genes of unknown function

Mutant phenotypes for thousands of bacterial genes of unknown function | Xanthomonas | Scoop.it
Morgan N. Price1, Kelly M. Wetmore1, r. Jordan Waters2, Mark callaghan1, Jayashree ray1, Hualan liu1, Jennifer V. Kuehl1, ryan A. Melnyk1, Jacob S. lamson1, Yumi Suh1, Hans K. carlson1, Zuelma esquivel1, Harini Sadeeshkumar1, romy chakraborty3, Grant M. Zane4, Benjamin e. rubin5, Judy D. Wall4, Axel Visel2,6, James Bristow2, Matthew J. Blow2*, Adam P. Arkin1,7* & Adam M. Deutschbauer

One-third of all protein-coding genes from bacterial genomes cannot be annotated with a function. Here, to investigate the functions of these genes, we present genome-wide mutant fitness data from 32 diverse bacteria across dozens of growth conditions. We identified mutant phenotypes for 11,779 protein-coding genes that had not been annotated with a specific function. Many genes could be associated with a specific condition because the gene affected fitness only in that condition, or with another gene in the same bacterium because they had similar mutant phenotypes. Of the poorly annotated genes, 2,316 had associations that have high confidence because they are conserved in other bacteria. By combining these conserved associations with comparative genomics, we identified putative DNA repair proteins; in addition, we propose specific functions for poorly annotated enzymes and transporters and for uncharacterized protein families. Our study demonstrates the scalability of microbial genetics and its utility for improving gene annotations.


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Unraveling the metabolic response of Brassica oleracea exposed to Xanthomonas campestris pv. campestris - Tortosa - 2018 - Journal of the Science of Food and Agriculture - Wiley Online Library

Results showed that Xcc infection causes dynamic changes in the metabolome of B. oleracea. Moreover, induction/ repression pattern of the metabolites implicated in the response follows a complex dynamics during infection progression, indicating a complex temporal response. Specific metabolic pathways such as alkaloids, coumarins or sphingolipids are postulated as promising key role candidates in the infection response.
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A Genome-Wide Screen Identifies Genes in Rhizosphere-Associated Pseudomonas Required to Evade Plant Defenses

A Genome-Wide Screen Identifies Genes in Rhizosphere-Associated Pseudomonas Required to Evade Plant Defenses | Xanthomonas | Scoop.it

Zhexian Liu, Polina Beskrovnaya, Ryan A. Melnyk, Sarzana S. Hossain, Sophie Khorasani, Lucy R. O’Sullivan, Christina L. Wiesmann, Jen Bush, Joël D. Richard, Cara H. Haneya, (2018)


Pseudomonas fluorescens and related plant root (“rhizosphere”)-associated species contribute to plant health by modulating defenses and facilitating nutrient uptake. To identify bacterial fitness determinants in the rhizosphere of the model plant Arabidopsis thaliana, we performed a high-throughput transposon sequencing (Tn-Seq) screen using the biocontrol and growth-promoting strain Pseudomonas sp. WCS365. The screen, which was performed in parallel on wild-type and immunocompromised Arabidopsis plants, identified 231 genes that increased fitness in the rhizosphere of wild-type plants. A subset of these genes decreased fitness in the rhizosphere of immunocompromised plants. We hypothesized that these genes might be involved in avoiding plant defenses and verified 7 Pseudomonas sp. WCS365 candidate genes by generating clean deletions. We found that two of these deletion mutants, Δ morA (encoding a putative diguanylate cyclase/phosphodiesterase) and Δ spuC (encoding a putrescine aminotransferase), formed enhanced biofilms and inhibited plant growth. We found that mutants ΔspuC and ΔmorA induced pattern-triggered immunity (PTI) as measured by induction of an Arabidopsis PTI reporter and FLS2 / BAK1- dependent inhibition of plant growth. We show that MorA acts as a phosphodiesterase to inhibit biofilm formation, suggesting a possible role in biofilm dispersal. We found that both putrescine and its precursor arginine promote biofilm formation that is enhanced in the ΔspuC mutant, which cannot break down putrescine, suggesting that putrescine might serve as a signaling molecule in the rhizosphere. Collectively, this work identified novel bacterial factors required to evade plant defenses in the rhizosphere.

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Database PlaD: A Transcriptomics Database for Plant Defense Responses to Pathogens, Providing New Insights into Plant Immune System

Database PlaD: A Transcriptomics Database for Plant Defense Responses to Pathogens, Providing New Insights into Plant Immune System | Xanthomonas | Scoop.it


High-throughput transcriptomics technologies have been widely used to study plant transcriptional reprogramming during the process of plant defense responses, and a large quantity of gene expression data have been accumulated in public repositories. However, utilization of these data is often hampered by the lack of standard metadata annotation. In this study, we curated 2444 public pathogenesis-related gene expression samples from the model plant Arabidopsis and three major crops (maize, rice, and wheat). We organized the data into a user-friendly database termed as PlaD. Currently, PlaD contains three key features. First, it provides large-scale curated data related to plant defense responses, including gene expression and gene functional annotation data. Second, it provides the visualization of condition-specific expression profiles. Third, it allows users to search co-regulated genes under the infections of various pathogens. Using PlaD, we conducted a large-scale transcriptome analysis to explore the global landscape of gene expression in the curated data. We found that only a small fraction of genes were differentially expressed under multiple conditions, which might be explained by their tendency of having more network connections and shorter network distances in gene networks. Collectively, we hope that PlaD can serve as an important and comprehensive knowledgebase to the community of plant sciences, providing insightful clues to better understand the molecular mechanisms underlying plant immune responses. PlaD is freely available at http://systbio.cau.edu.cn/plad/index.php or http://zzdlab.com/plad/index.php.
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Glutamate triggers long-distance, calcium-based plant defense signaling

Glutamate triggers long-distance, calcium-based plant defense signaling | Xanthomonas | Scoop.it

[NICE VIDEOS]


A plant injured on one leaf by a nibbling insect can alert its other leaves to begin anticipatory defense responses. Working in the model plant Arabidopsis , Toyota et al. show that this systemic signal begins with the release of glutamate, which is perceived by glutamate receptor–like ion channels (see the Perspective by Muday and Brown-Harding). The ion channels then set off a cascade of changes in calcium ion concentration that propagate through the phloem vasculature and through intercellular channels called plasmodesmata. This glutamate-based long-distance signaling is rapid: Within minutes, an undamaged leaf can respond to the fate of a distant leaf.

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A conserved motif promotes HpaB-regulated export of type III effectors from Xanthomonas.

A conserved motif promotes HpaB-regulated export of type III effectors from Xanthomonas. | Xanthomonas | Scoop.it
The type III‐secretion (T3S) system, an essential pathogenicity factor in most Gram‐negative plant‐pathogenic bacteria, injects bacterial effector proteins directly into the plant cell cytosol. Here, the type III effectors (T3Es) manipulate host cell processes to suppress defense and establish proper conditions for bacterial multiplication in the intercellular spaces of the plant tissue. T3E export depends on a secretion signal which is also present in “non‐effectors”. The latter are secreted extracellular components of the T3S apparatus, but they are not translocated into the plant cell. How the T3S system discriminates between T3Es and non‐effectors is still enigmatic. Previously, we identified a putative translocation motif (TrM) in several T3Es from Xanthomonas campestris pv. vesicatoria (Xcv). Here, we analyzed the TrM of the Xcv effector XopB in detail. Mutation studies showed that the proline/arginine‐rich motif is required for efficient type III‐dependent secretion and translocation of XopB and determines dependency of XopB transport on the general T3S chaperone HpaB. Similar results were obtained for other effectors from Xcv. Since the arginine residues of the TrM mediate specific binding of XopB to cardiolipin, one of the major lipid components in Xanthomonas membranes, we assume that association of T3Es to the bacterial membrane prior to secretion supports type III‐dependent export.
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Xanthomonas oryzae pv. oryzae chemotaxis components and chemoreceptor Mcp2 is involved in sensing constituent of xylem sap and contribute to regulation of virulence associated functions and entry i...

Xanthomonas oryzae pv. oryzae chemotaxis components and chemoreceptor Mcp2 is involved in sensing constituent of xylem sap and contribute to regulation of virulence associated functions and entry i... | Xanthomonas | Scoop.it
Raj Kumar, Verma Biswajit Samal &  Subhadeep Chatterjee (2018)

The Xanthomonas group of phytopathogens causes several economically important diseases in crops. In the bacterial pathogen of rice, Xanthomonas oryzae pv. oryzae (Xoo), it has been proposed that chemotaxis may play a role in the entry and colonization of the pathogen inside the host. However, components of the chemotaxis system, including chemoteceptor involved, and their role in entry and virulence is not well defined. In this study we show that Xoo displayed a positive chemotaxis response to components of rice xylem sap, glutamine, xylose, methionine. In order to understand the role of chemotaxis components involved in promoting chemotaxis, entry and virulence, we performed detailed deletion mutant analysis. Analysis of mutants defective in chemotaxis components, flagellar‐biogenesis, expression analysis and assays of virulence associated functions indicated that chemotaxis‐mediated signaling in Xoo is involved in the regulation of several viriulence associated functions such as motility, attachment and iron homeostasis. The ∆cheY1 mutant of Xoo exhibited a reduced expression of genes involved in motility, adhesins, and iron uptake and metabolism. We show that the expression of Xoo chemotaxis and motility components are induced under in planta condition and is required for entry, colonization and virulence. Furthermore, deletion analysis of a putative chemoreceptor mcp2 gene revealed that chemoreceptor Mcp2 is involved in sensing xylem sap and constituents of xylem exudate including methionine, serine and histidine, and plays an important role in epiphytic entry and virulence. This is the first report of the role of chemotaxis in the virulence of this important group of phytopathogens.
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Genotyping-by-sequencing of Brassica oleracea vegetables reveals unique phylogenetic patterns, population structure and domestication footprints

Genotyping-by-sequencing of Brassica oleracea vegetables reveals unique phylogenetic patterns, population structure and domestication footprints | Xanthomonas | Scoop.it

Zachary Stansell, Katie Hyma, Jonathan Fresnedo-Ramírez, Qi Sun, Sharon Mitchell, Thomas Björkman & Jian Hua (2018)


A comparison of gene variations in modern-day offspring of wild cabbage shows that broccoli may have preceded the appearance of cauliflower in domesticated crops. Jian Hua, Thomas Bjorkman, and colleagues from Cornell University in the US examined the DNA sequences of 85 traditional “landrace” and improved broccoli, cauliflower, and Chinese kale plants, all of which descend from the species Brassica oleracea, or wild cabbage. They found 21,680 sequence variations among them all, which they used to look for patterns of relatedness between the plants. Their results support the possible domestication of cauliflower after or in parallel with broccoli. The study identifies a large pool of genetic diversity within broccoli landraces that could be used to improve future breeding efforts.

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Lifestyle of the biotroph Agrobacterium tumefaciens in the ecological niche constructed on its host plant - González‐Mula - 2018 - New Phytologist - Wiley Online Library

Lifestyle of the biotroph Agrobacterium tumefaciens in the ecological niche constructed on its host plant - González‐Mula - 2018 - New Phytologist - Wiley Online Library | Xanthomonas | Scoop.it
Agrobacterium tumefaciens constructs an ecological niche in its host plant by transferring the T-DNA from its Ti plasmid into the host genome and by diverting the host metabolism.  We combined transcriptomics and genetics for understanding the A. tumefaciens lifestyle when it colonizes Arabidopsis thaliana tumors. Transcriptomics highlighted: a transition from a motile to sessile behavior that mobilizes some master regulators (Hfq, CtrA, DivK and PleD); a remodeling of some cell surface compo- nents (O-antigen, succinoglucan, curdlan, att genes, putative fasciclin) and functions associ- ated with plant defense (Ef-Tu and flagellin pathogen-associated molecular pattern-response and glycerol-3-phosphate and nitric oxide signaling); and an exploitation of a wide variety of host resources, including opines, amino acids, sugars, organic acids, phosphate, phosphory- lated compounds, and iron. In addition, construction of transgenic A. thaliana lines expressing a lactonase enzyme showed that Ti plasmid transfer could escape host-mediated quorum- quenching. Finally, construction of knock-out mutants in A. tumefaciens showed that expres- sion of some At plasmid genes seemed more costly than the selective advantage they would have conferred in tumor colonization.  We provide the first overview of A. tumefaciens lifestyle in a plant tumor and reveal novel signaling and trophic interplays for investigating host–pathogen interactions.

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High-Throughput Screening of Type III Secretion Determinants Reveals a Major Chaperone-Independent Pathway

Nadja Heinz Ernst, Analise Z. Reeves, Julia E. Ramseyer, Cammie F. Lesser

Numerous Gram-negative bacterial pathogens utilize type III secretion systems (T3SSs) to inject tens of effector proteins directly into the cytosol of host cells. Through interactions with cognate chaperones, type III effectors are defined and recruited to the sorting platform, a cytoplasmic component of these membrane-embedded nanomachines. However, notably, a comprehensive review of the literature reveals that the secretion of most type III effectors has not yet been linked to a chaperone, raising questions regarding the existence of unknown chaperones as well as the universality of chaperones in effector secretion. Here, we describe the development of the first high-throughput type III secretion (T3S) assay, a semiautomated solid-plate-based assay, which enables the side-by-side comparison of secretion of over 20 Shigella effectors under a multitude of conditions. Strikingly, we found that the majority of Shigella effectors are secreted at equivalent levels by wild-type and variants of Shigella that no longer encode one or all known Shigella T3S effector chaperones. In addition, we found that Shigella effectors are efficiently secreted from a laboratory strain of Escherichia coli expressing the core Shigella type III secretion apparatus (T3SA) but no other Shigella-specific proteins. Furthermore, we observed that the sequences necessary and sufficient to define chaperone-dependent and -independent effectors are fundamentally different. Together, these findings support the existence of a major, previously unrecognized, noncanonical chaperone-independent secretion pathway that is likely common to many T3SSs.
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Network biology discovers pathogen contact points in host protein-protein interactomes

Network biology discovers pathogen contact points in host protein-protein interactomes | Xanthomonas | Scoop.it

Hadia Ahmed, T.C. Howton, Yali Sun, Natascha Weinberger, Youssef Belkhadir & M. Shahid Mukhtar


Nodes with high centrality in protein–protein interaction (PPI) networks are known to be essential in some organisms. Here, the authors in contrast find that in the interactome of A. thaliana central nodes are enriched in conditional and immune phenotypes and are preferred targets of pathogens.

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Peptidoglycan hydrolysis mediated by the amidase AmiC and its LytM activator NlpD is critical for cell separation and virulence in the phytopathogen Xanthomonas campestris

Peptidoglycan hydrolysis mediated by the amidase AmiC and its LytM activator NlpD is critical for cell separation and virulence in the phytopathogen Xanthomonas campestris | Xanthomonas | Scoop.it
Li‐Chao Yang Yong‐Liang Gan Li‐Yan Yang Bo‐Le Jiang and Ji‐Liang Tang

The essential stages of bacterial cell separation are described as the synthesis and hydrolysis of septal peptidoglycan (PG). The amidase, AmiC, which cleaves the peptide side‐chains linked to the glycan strands, contributes critically to this process and has been studied extensively in model strains of Escherichia coli. However, insights into the contribution of this protein to other processes in the bacterial cell have been limited. Xanthomonas campestris pv. campestris (Xcc) is a phytopathogen that causes black rot disease in many economically important plants. We investigated how AmiC and LytM family regulators, NlpD and EnvC, contribute to virulence and cell separation in this organism. Biochemical analyses of purified AmiC demonstrated that it could hydrolyse PG and its activity could be potentiated by the presence of the regulator NlpD. We also established that deletion of the genes encoding amiC1 or nlpD led to a reduction in virulence as well as effects on colony‐forming units and cell morphology. Moreover, further genetic and biochemical evidence showed that AmiC1 and NlpD affect the secretion of type III effector XC3176 and hypersensitive response (HR) induction in planta. These findings indicate that, in addition to their well‐studied role(s) in cell separation, AmiC and NlpD make an important contribution to the type III secretion (T3S) and virulence regulation in this important plant pathogen.
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Plant–Pathogen Warfare under Changing Climate Conditions

Plant–Pathogen Warfare under Changing Climate Conditions | Xanthomonas | Scoop.it
Andre C. Velasquez, Christian Danve M. Castroverde, and Sheng Yang He (2018)

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 21st 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 CO2 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.
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