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Genome-wide characterization and expression profiling of SWEET genes in cabbage (Brassica oleracea var. capitata L.) reveal their roles in chilling and clubroot disease responses | BMC Genomics | F...

Genome-wide characterization and expression profiling of SWEET genes in cabbage (Brassica oleracea var. capitata L.) reveal their roles in chilling and clubroot disease responses | BMC Genomics | F... | Xanthomonas | Scoop.it
The SWEET proteins are a group of sugar transporters that play a role in sugar efflux during a range of biological processes, including stress responses. However, there has been no comprehensive analysis of the SWEET family genes in Brassica oleracea (BoSWEET), and the evolutionary pattern, phylogenetic relationship, gene characteristics of BoSWEET genes and their expression patterns under biotic and abiotic stresses remain largely unexplored. A total of 30 BoSWEET genes were identified and divided into four clades in B. oleracea. Phylogenetic analysis of the BoSWEET proteins indicated that clade II formed first, followed by clade I, clade IV and clade III, successively. Clade III, the newest clade, shows signs of rapid expansion. The Ks values of the orthologous SWEET gene pairs between B. oleracea and Arabidopsis thaliana ranged from 0.30 to 0.45, which estimated that B. oleracea diverged from A. thaliana approximately 10 to 15 million years ago. Prediction of transmembrane regions showed that eight BoSWEET proteins contain one characteristic MtN3_slv domain, twenty-one contain two, and one has four. Quantitative reverse transcription-PCR (qRT-PCR) analysis revealed that five BoSWEET genes from clades III and IV exhibited reduced expression levels under chilling stress. Additionally, the expression levels of six BoSWEET genes were up-regulated in roots of a clubroot-susceptible cabbage cultivar (CS-JF1) at 7 days after inoculation with Plasmodiophora brassicae compared with uninoculated plants, indicating that these genes may play important roles in transporting sugars into sink roots associated with P. brassicae colonization in CS-JF1. Subcellular localization analysis of a subset of BoSWEET proteins indicated that they are localized in the plasma membrane. This study provides important insights into the evolution of the SWEET gene family in B. oleracea and other species, and represents the first study to characterize phylogenetic relationship, gene structures and expression patterns of the BoSWEET genes. These findings provide new insights into the complex transcriptional regulation of BoSWEET genes, as well as potential candidate BoSWEET genes that promote sugar transport to enhance chilling tolerance and clubroot disease resistance in cabbage.
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Molecules and Cells

Molecules and Cells | Xanthomonas | Scoop.it

A Genome-Scale Co-Functional Network of Xanthomonas Genes Can Accurately Reconstruct Dégueulatoire Circuits Controlled by Two-Component Signaling Systems


Bacterial species in the genus Xanthomonas infect virtually all crop plants. Although many genes involved in Xanthomonas virulence have been identified through molecular and cellular studies, the elucidation of virulence-associated regulatory circuits is still far from complete. Functional gene networks have proven useful in generating hypotheses for genetic factors of biological processes in various species. Here, we present a genome-scale co-functional network of Xanthomonas oryze pv. oryzae (Xoo) genes, XooNet (www.inetbio.org/xoonet/), constructed by integrating heterogeneous types of genomics data derived from Xoo and other bacterial species. XooNet contains 106,000 functional links, which cover approximately 83% of the coding genome. XooNet is highly predictive for diverse biological processes in Xoo and can accurately reconstruct cellular pathways regulated by two-component signaling transduction systems (TCS). XooNet will be a useful in silico research platform for genetic dissection of virulence pathways in Xoo.

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Global Transcriptome Profiling of Xanthomonas oryzae pv. oryzae under in planta Growth and in vitro Culture Conditions

Global Transcriptome Profiling of Xanthomonas oryzae pv. oryzae under in planta Growth and in vitro Culture Conditions | Xanthomonas | Scoop.it
Xanthomonas oryzae pv. oryzae (Xoo), the causative agent of bacterial blight, is a major threat to rice productivity. Here, we performed RNA-Seq based transcriptomic analysis of Xoo transcripts isolated under in planta growth (on both susceptible an
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Systems and synthetic biology perspective of the versatile plant-pathogenic and polysaccharide-producing bacterium Xanthomonas campestris

Systems and synthetic biology perspective of the versatile plant-pathogenic and polysaccharide-producing bacterium Xanthomonas campestris | Xanthomonas | Scoop.it
Sarah Schatschneider, 1, *‡ Jessica Schneider, 2 ‡ Jochen Blom, 3 Fabien Letisse, 4 Karsten Niehaus, 1 Alexander Goesmann 3 † and Frank-Jörg Vorhölter 5 †§

Abstract : Bacteria of the genus Xanthomonas are a major group of plant pathogens. They are hazardous to important crops and closely related to human pathogens. Being collectively a major focus of molecular phytopathology, an increasing number of diverse and intricate mechanisms are emerging by which they communicate, interfere with host signalling and keep competition at bay. Interestingly, they are also biotechnologically relevant polysaccharide producers. Systems biotechnology techniques have revealed their central metabolism and a growing number of remarkable features. Traditional analyses of Xanthomonas metabolism missed the Embden–Meyerhof–Parnas pathway (glycolysis) as being a route by which energy and molecular building blocks are derived from glucose. As a consequence of the emerging full picture of their metabolism process, xanthomonads were discovered to have three alternative catabolic pathways and they use an unusual and reversible phosphofructokinase as a key enzyme. In this review, we summarize the synthetic and systems biology methods and the bioinformatics tools applied to reconstruct their metabolic network and reveal the dynamic fluxes within their complex carbohydrate metabolism. This is based on insights from omics disciplines; in particular, genomics, transcriptomics, proteomics and metabolomics. Analysis of high-throughput omics data facilitates the reconstruction of organism-specific large- and genome-scale metabolic networks. Reconstructed metabolic networks are fundamental to the formulation of metabolic models that facilitate the simulation of actual metabolic activities under specific environmental conditions.

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2016 GEORGIA PLANT DISEASE LOSS ESTIMATES



In 2016, Georgia’s plant disease losses, including control costs, amounted to an estimated $821 million. The value of the crops used in this estimate was approximately $6,596 million, resulting in a 12.8% relative disease loss across all crops included in this summary. The estimated values for most crops used to compute these disease losses are summarized in the UGA Center for Agribusiness and Economic Development’s 2016 Georgia Farm Gate Value Report (AR-17-01). Some estimates for fruits, ornamentals, and turf rely on specialists’ knowledge of the industry and industry sources for information.

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Dual-barcoded shotgun expression library sequencing for high-throughput characterization of functional traits in bacteria

Dual-barcoded shotgun expression library sequencing for high-throughput characterization of functional traits in bacteria | Xanthomonas | Scoop.it
Gain of function methods based on gene overexpression are not easily applied to high-throughput screening across different experimental conditions. Here, the authors present Dub-seq, which separates overexpression library characterization from functional screening and uses random DNA barcodes to increase the experimental throughput.
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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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Frontiers | Transcriptional Reprogramming of Rice Cells by Xanthomonas oryzae TALEs | Plant Science

Frontiers | Transcriptional Reprogramming of Rice Cells by Xanthomonas oryzae TALEs | Plant Science | Xanthomonas | Scoop.it
Rice-pathogenic Xanthomonas oryzae bacteria cause severe harvest loss and challenge a stable food supply. The pathogen virulence relies strongly on bacterial TALE (transcription activator-like effector) proteins that function as transcriptional activators inside the plant cell. To understand the plant targets of TALEs, we determined the genome sequences of the Indian X. oryzae pv. oryzae (Xoo) type strain ICMP 3125T and the strain PXO142 from the Philippines. Their complete TALE repertoire was analyzed and genome-wide TALE targets in rice were characterized. Integrating computational target predictions and rice transcriptomics data, we were able to verify 12 specifically induced target rice genes. The TALEs of the Xoo strains were reconstructed and expressed in a TALE-free Xoo strain to attribute specific induced genes to individual TALEs. Using reporter assays, we could show that individual TALEs act directly on their target promoters. In particular, we show that TALE classes assigned by AnnoTALE reflect common target genes, and that TALE classes of Xoo and the related pathogen X. oryzae pv. oryzicola share more common target genes than previously believed. Taken together, we establish a detailed picture of TALE-induced plant processes that significantly expands our understanding of X. oryzae virulence strategies and will facilitate the development of novel resistances to overcome this important rice disease.
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IJMS | Free Full-Text | Small Molecule Inhibitors Specifically Targeting the Type III Secretion System of Xanthomonas oryzae on Rice

IJMS | Free Full-Text | Small Molecule Inhibitors Specifically Targeting the Type III Secretion System of Xanthomonas oryzae on Rice | Xanthomonas | Scoop.it

Diffusible signal factor (DSF)-mediated quorum sensing modulates expression of diverse traits in Xanthomonas citri and responses of citrus plants to promote disease



The initiative strategy for the development of novel anti-microbial agents usually uses the virulence factors of bacteria as a target, without affecting their growth and survival. The type III secretion system (T3SS), one of the essential virulence factors in most Gram-negative pathogenic bacteria because of its highly conserved construct, has been regarded as an effective target that developed new anti-microbial drugs. Xanthomonas oryzae pv. oryzae (Xoo) causes leaf blight diseases and is one of the most important pathogens on rice. To find potential anti-virulence agents against this pathogen, a number of natural compounds were screened for their effects on the T3SS of Xoo. Three of 34 compounds significantly inhibited the promoter activity of the harpin gene, hpa1, and were further checked for their impact on bacterial growth and on the hypersensitive response (HR) caused by Xoo on non-host tobacco plants. The results indicated that treatment of Xoo with CZ-1, CZ-4 and CZ-9 resulted in an obviously attenuated HR without affecting bacterial growth and survival. Moreover, quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis showed that the expression of the Xoo T3SS was suppressed by treatment with the three inhibitors. The mRNA levels of representative genes in the hypersensitive response and pathogenicity (hrp) cluster, as well as the regulatory genes hrpG and hrpX, were reduced. Finally, the in vivo test demonstrated that the compounds could reduce the disease symptoms of Xoo on the rice cultivar (Oryza sativa) IR24.

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Diffusible signal factor (DSF)-mediated quorum sensing modulates expression of diverse traits in Xanthomonas citri and responses of citrus plants to promote disease

Diffusible signal factor (DSF)-mediated quorum sensing modulates expression of diverse traits in Xanthomonas citri and responses of citrus plants to promote disease | Xanthomonas | Scoop.it
The gram-negative Xanthomonas genus contains a large group of economically important plant pathogens, which cause severe diseases on many crops worldwide. The diffusible signal factor (DSF) - mediated quorum sensing (QS) system coordinates expressio
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[Review] The Role of Proteases in the Virulence of Plant Pathogenic Bacteria

[Review] The Role of Proteases in the Virulence of Plant Pathogenic Bacteria | Xanthomonas | Scoop.it
A pathogenic lifestyle is inextricably linked with the constant necessity of facing various challenges exerted by the external environment (both within and outside the host). To successfully colonize the host and establish infection, pathogens have evolved sophisticated systems to combat the host defense mechanisms and also to be able to withstand adverse environmental conditions. Proteases, as crucial components of these systems, are involved in a variety of processes associated with infection. In phytopathogenic bacteria, they play important regulatory roles and modulate the expression and functioning of various virulence factors. Secretory proteases directly help avoid recognition by the plant immune systems, and contribute to the deactivation of the defense response pathways. Finally, proteases are important components of protein quality control systems, and thus enable maintaining homeostasis in stressed bacterial cells. In this review, we discuss the known protease functions and protease-regulated signaling processes associated with virulence of plant pathogenic bacteria.
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Dissecting quantitative resistance to Xanthomonas campestris pv. campestris in leaves of Brassica oleracea by QTL analysis

Dissecting quantitative resistance to Xanthomonas campestris pv. campestris in leaves of Brassica oleracea by QTL analysis | Xanthomonas | Scoop.it

Laura Iglesias-Bernabé, Pari Madloo, Víctor Manuel Rodríguez, Marta Francisco & Pilar Soengas


Black rot, caused by the bacterium Xanthomonas campestris pv. campestris (Xcc), produces important economic losses in crops of Brassica oleracea worldwide. Resistance to race 1, the most virulent and widespread in B. oleracea, is under quantitative control. Knowledge about the genetics of this resistance would help in designing strategies to control initial stages of invasion and development of the disease. QTL analysis of the resistance in the BolTBDH mapping population was performed. Resistance was measured with five traits related to initial stages of the invasion, success of infection and spread of the pathogen. Four single-trait QTLs of resistance were found, from which one represent novel variation. After performing multi-trait QTL, we concluded that spread of Xcc is related to the size of the leaf. Individuals from the mapping population follow two different strategies to cope with the spread of the disease: reducing lesion size or maintain more area of the leaf photosynthetically active, being more tolerant to Xcc invasion. Mechanisms underlying variation for resistance may be related to different aspects of plant immunity, including the synthesis of glucosinolates and phenolics.

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Rampant Cheating by Pathogens?

Pathogenic bacteria often cooperate during infection. Communication through quorum sensing allows bacteria to coordinate gene expression in a population density–dependent manner; biofilm formation increases population resistance to host- and antibiotic-related stresses. Although such cooperative behaviors benefit pathogens at the population level, individual cells experience costs of cooperation. “Cheater” mutants may arise that avoid these costs while exploiting the “public goods” produced by cooperative cells. Recent research has highlighted that, surprisingly, the bacterial type III secretion system (T3SS) can serve as a “public good” during infection. This structure is produced by multiple Gram-negative bacteria and is used to inject proteins that modulate host biology (effectors) directly into host cells. Often, T3SS-secreted effectors alter immune responses in a way that benefits bacteria at a local population level in the infected host. This cooperative function is subject to exploitation by cheater mutants lacking a T3SS but benefiting from secretion by wild-type cooperators. Here, we review examples of T3SS cheaters, consider fitness costs associated with producing the T3SS, and discuss mechanisms that can reduce the risk of cheater emergence in infected hosts.
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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

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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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