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Applied Env. Microb. (2012): The bacterium Pantoea stewartii uses two different type III secretion systems for colonizing its plant host and insect vector

Applied Env. Microb. (2012): The bacterium Pantoea stewartii uses two different type III secretion systems for colonizing its plant host and insect vector | Effectors and Plant Immunity | Scoop.it

Plant and animal-pathogenic bacteria utilize phylogenetically distinct type III secretion systems (T3SS) that produce needle-like injectisomes or pili for the delivery of effector proteins into host cells. Pantoea stewartii subsp. stewartii (Pnss), the causative agent of Stewart's bacterial wilt and leaf blight of maize, carries phylogenetically distinct T3SSs. In addition to an Hrc-Hrp T3SS, known to be essential for maize pathogenesis, Pnss has a second T3SS (PSI-2) that is required for persistence in its flea beetle vector, Chaetocnema pulicaria (Melsh). PSI-2 belongs to the Inv-Mxi-Spa T3SS family typically found in animal pathogens. Mutagenesis of the PSI-2 psaN gene, which encodes an ATPase essential for secretion of T3SS effectors by the injectisome, greatly reduces both the persistence of Pnss in flea beetle guts and the beetle's ability to transmit Pnss to maize. Ectopic expression of the psaN gene complements these phenotypes. In addition, the PSI-2 psaN gene is not required for Pnss pathogenesis of maize and is transcriptionally up-regulated in insects compared to maize tissues. Thus, the Hrp and PSI-2 T3SSs play different roles in the life cycle of Pnss as it alternates between its insect vector and plant host.

 

Valdir R. Correa, Doris R. Majerczak, El-Desouky Ammar, Massimo Merighi, Richard C. Pratt, Saskia A. Hogenhout, David L. Coplin and Margaret G. Redinbaugh

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Effectors and Plant Immunity
Strategies of plant defense and microbe attacks
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Front. Plant Sci./Front. Microbiol.: Genomics and Effectomics of the crop killer Xanthomonas

Front. Plant Sci./Front. Microbiol.: Genomics and Effectomics of the crop killer Xanthomonas | Effectors and Plant Immunity | Scoop.it

Published articles:

 

9. Research article by ÜStun et al.: The Xanthomonas effector XopJ triggers a conditional hypersensitive response upon treatment of N. benthamiana leaves with salicylic acid. Front. Plant Sci. (2015)

 

8. Methods by Pérez-Quintero et al.:  QueTAL: a suite of tools to classify and compare TAL effectors functionally and phylogenetically. Front. Plant Sci. (2015)

 

7. Hypothesis and theory by Wilkins et al.: TAL effectors and activation of predicted host targets distinguish Asian from African strains of the rice pathogen Xanthomonas oryzae pv. oryzicola while strict conservation suggests universal importance of five TAL effectors. Front. Plant Sci. (2015)

 

6. Review by Hutin et al.: MorTAL Kombat: the story of defense against TAL effectors through loss-of-susceptibility. Front. Plant Sci. (2015)

 

5. Research article by Jacobs et al.: Comparative genomics of a cannabis pathogen reveals insight into the evolution of pathogenicity in Xanthomonas. Front. Plant Sci. (2015)

 

4. Research article by Schwartz et al.: Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity. Front. Microbiol. (2015)

 

3. Perspective by Dossa et al.: Decision tools for bacterial blight resistance gene deployment in rice-based agricultural ecosystems. Front. Plant Sci. (2015)

 

2. Mini-review by Pieretti et al.: What makes Xanthomonas albilineans unique amongst xanthomonads? Front. Plant Sci. (2015)

 

1. Mini-review by S. Üstün and F. Börnke: Interactions of Xanthomonas type-III effector proteins with the plant ubiquitin and ubiquitin-like pathways. Front. Plant Sci. (2014)

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Suayib Üstün's curator insight, July 29, 2014 2:57 PM

Great topic-excited!

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New Phytologist: Standards for plant synthetic biology: a common syntax for exchange of DNA parts (2015)

New Phytologist: Standards for plant synthetic biology: a common syntax for exchange of DNA parts (2015) | Effectors and Plant Immunity | Scoop.it

Inventors in the field of mechanical and electronic engineering can access multitudes of components and, thanks to standardization, parts from different manufacturers can be used in combination with each other. The introduction of BioBrick standards for the assembly of characterized DNA sequences was a landmark in microbial engineering, shaping the field of synthetic biology. Here, we describe a standard for Type IIS restriction endonuclease-mediated assembly, defining a common syntax of 12 fusion sites to enable the facile assembly of eukaryotic transcriptional units. This standard has been developed and agreed by representatives and leaders of the international plant science and synthetic biology communities, including inventors, developers and adopters of Type IIS cloning methods. Our vision is of an extensive catalogue of standardized, characterized DNA parts that will accelerate plant bioengineering.

 

Nicola J. Patron, Diego Orzaez, Sylvestre Marillonnet, Heribert Warzecha, Colette Matthewman, Mark Youles, Oleg Raitskin, Aymeric Leveau, Gemma Farré, Christian Rogers, Alison Smith, Julian Hibberd, Alex A. R. Webb, James Locke, Sebastian Schornack, Jim Ajioka, David C. Baulcombe, Cyril Zipfel, Sophien Kamoun, Jonathan D. G. Jones, Hannah Kuhn, Silke Robatzek, H. Peter Van Esse, Dale Sanders, Giles Oldroyd, Cathie Martin, Rob Field, Sarah O'Connor, Samantha Fox, Brande Wulff, Ben Miller, Andy Breakspear, Guru Radhakrishnan, Pierre-Marc Delaux, Dominique Loqué, Antonio Granell, Alain Tissier, Patrick Shih, Thomas P. Brutnell, W. Paul Quick, Heiko Rischer, Paul D. Fraser, Asaph Aharoni, Christine Raines, Paul F. South, Jean-Michel Ané, Björn R. Hamberger, Jane Langdale, Jens Stougaard, Harro Bouwmeester, Michael Udvardi, James A. H. Murray, Vardis Ntoukakis, Patrick Schäfer, Katherine Denby, Keith J. Edwards, Anne Osbourn, and Jim Haseloff


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The Sainsbury Lab's curator insight, July 14, 12:25 PM

Inventors in the field of mechanical and electronic engineering can access multitudes of components and, thanks to standardization, parts from different manufacturers can be used in combination with each other. The introduction of BioBrick standards for the assembly of characterized DNA sequences was a landmark in microbial engineering, shaping the field of synthetic biology. Here, we describe a standard for Type IIS restriction endonuclease-mediated assembly, defining a common syntax of 12 fusion sites to enable the facile assembly of eukaryotic transcriptional units. This standard has been developed and agreed by representatives and leaders of the international plant science and synthetic biology communities, including inventors, developers and adopters of Type IIS cloning methods. Our vision is of an extensive catalogue of standardized, characterized DNA parts that will accelerate plant bioengineering.

Rescooped by Nicolas Denancé from Plant-microbe interaction
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Two serine residues in Pseudomonas syringae effector HopZ1a are required for acetyltransferase activity and association with the host co-factor - Ma - 2015 - New Phytologist - Wiley Online Library

Two serine residues in Pseudomonas syringae effector HopZ1a are required for acetyltransferase activity and association with the host co-factor - Ma - 2015 - New Phytologist - Wiley Online Library | Effectors and Plant Immunity | Scoop.it
Summary
Gram-negative bacteria inject type III secreted effectors (T3SEs) into host cells to manipulate the immune response. The YopJ family effector HopZ1a produced by the plant pathogen Pseudomonas syringae possesses acetyltransferase activity and acetylates plant proteins to facilitate infection.
Using mass spectrometry, we identified a threonine residue, T346, as the main autoacetylation site of HopZ1a. Two neighboring serine residues, S349 and S351, are required for the acetyltransferase activity of HopZ1a in vitro and are indispensable for the virulence function of HopZ1a in Arabidopsis thaliana.
Using proton nuclear magnetic resonance (NMR), we observed a conformational change of HopZ1a in the presence of inositol hexakisphosphate (IP6), which acts as a eukaryotic co-factor and significantly enhances the acetyltransferase activity of several YopJ family effectors. S349 and S351 are required for IP6-binding-mediated conformational change of HopZ1a.
S349 and S351 are located in a conserved region in the C-terminal domain of YopJ family effectors. Mutations of the corresponding serine(s) in two other effectors, HopZ3 of P. syringae and PopP2 of Ralstonia solanacerum, also abolished their acetyltransferase activity. These results suggest that, in addition to the highly conserved catalytic residues, YopJ family effectors also require conserved serine(s) in the C-terminal domain for their enzymatic activity.

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MPP: Identification of novel Xanthomonas euvesicatoria type III effector proteins by a machine-learning approach (2015)

MPP: Identification of novel Xanthomonas euvesicatoria type III effector proteins by a machine-learning approach (2015) | Effectors and Plant Immunity | Scoop.it
The Gram-negative bacterium Xanthomonas euvesicatoria (Xcv) is the causal agent of bacterial spot disease in pepper and tomato. Xcv pathogenicity depends on a type III secretion (T3S) system that delivers effector proteins into host cells to suppress plant immunity and promote disease. The pool of known Xcv effectors includes approximately 30 proteins, most of them identified in the 85-10 strain by various experimental and computational techniques. To identify additional Xcv 85-10 effectors, we applied a genome-wide machine learning approach, in which all ORFs were scored according to their propensity to encode effectors. Scoring was based on a large set of features including genomic organization, taxonomical dispersion, hrp-dependent expression, 5’ regulatory sequences, amino acid composition bias, and GC content. Thirty-six predicted effectors were tested for translocation into plant cells by using the HR-inducing domain of AvrBs2 as a reporter. Seven proteins (XopAU, XopAV, XopAW, XopAP, XopAX, XopAK, and XopAD) harbored a functional translocation signal and their translocation relied on the HrpF translocon, indicating that they are bona fide T3S effectors. Remarkably, four of them belong to novel effector families. Inactivation of the xopAP gene reduced the severity of disease symptoms in infected plants. A decrease in cell death and chlorophyll content was observed in pepper leaves inoculated with the xopAP mutant as compared to the wild-type strain. However, populations of the xopAP mutant in infected leaves were similar in size to those of the wild-type bacteria, suggesting that the reduction in virulence was not due to an impaired bacterial growth.

Via Suayib Üstün, Jim Alfano
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mBio: A TALE of Transposition: Tn3-Like Transposons Play a Major Role in the Spread of Pathogenicity Determinants of Xanthomonas citri and Other Xanthomonads (2015)

mBio: A TALE of Transposition: Tn3-Like Transposons Play a Major Role in the Spread of Pathogenicity Determinants of Xanthomonas citri and Other Xanthomonads (2015) | Effectors and Plant Immunity | Scoop.it

Members of the genus Xanthomonas are among the most important phytopathogens. A key feature of Xanthomonas pathogenesis is the translocation of type III secretion system (T3SS) effector proteins (T3SEs) into the plant target cells via a T3SS. Several T3SEs and a murein lytic transglycosylase gene (mlt, required for citrus canker symptoms) are found associated with three transposition-related genes in Xanthomonas citri plasmid pXAC64. These are flanked by short inverted repeats (IRs). The region was identified as a transposon, TnXax1, with typical Tn3 family features, including a transposase and two recombination genes. Two 14-bp palindromic sequences within a 193-bp potential resolution site occur between the recombination genes. Additional derivatives carrying different T3SEs and other passenger genes occur in different Xanthomonas species. The T3SEs include transcription activator-like effectors (TALEs). Certain TALEs are flanked by the same IRs as found in TnXax1 to form mobile insertion cassettes (MICs), suggesting that they may be transmitted horizontally. A significant number of MICs carrying other passenger genes (including a number of TALE genes) were also identified, flanked by the same TnXax1 IRs and delimited by 5-bp target site duplications. We conclude that a large fraction of T3SEs, including individual TALEs and potential pathogenicity determinants, have spread by transposition and that TnXax1, which exhibits all of the essential characteristics of a functional transposon, may be involved in driving MIC transposition. We also propose that TALE genes may diversify by fork slippage during the replicative Tn3 family transposition. These mechanisms may play a crucial role in the emergence of Xanthomonas pathogenicity.


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Plant denizens get the big-science treatment

Plant denizens get the big-science treatment | Effectors and Plant Immunity | Scoop.it

A plant may be rooted in place, but it is never lonely. There are bacteria in, on and near it, munching away on their host, on each other, on compounds in the soil. Amoebae dine on bacteria, nematodes feast on roots, insects devour fruit — with consequences for the chemistry of the soil, the taste of a leaf or the productivity of a crop.

 

From 30 June to 2 July, more than 200 researchers gathered in Washington DC for the first meeting of the Phytobiomes Initiative, an ambitious proposal to catalogue and characterize a plant’s most intimate associates and their impact on agriculture. By the end of the year, attendees hope to carve out a project that will apply this knowledge in ways that will appeal to funders in industry and government.

 

“We want to get more money,” says plant pathologist Linda Kinkel at the University of Minnesota in St Paul. “But beyond that, let’s just all try to talk the same language and come up with some shared goals.”

 

Leach coined the term phytobiome in 2013,at a retreat about food security. She defines the phytobiome broadly, to encompass microbes, insects, nematodes and plants as well as the abiotic factors that influence all these.

 

Since then, she has visited companies, funding agencies and universities to call for a unifying phytobiomes initiative. She has teamed up with Kellye Eversole, a consultant based in Bethesda, Maryland, and the co-owner of a small family farm in Oklahoma, who has experience working on large agricultural genomics projects, including the US National Plant Genome Initiative. That initiative was launched in 1998 and continues to crank out databases and other tools for analysing plant genomes.

 

Leach hopes that the Phytobiomes Initiative will leave a similar legacy, but she is mindful that federal funding has tightened considerably since 1998. Still, she notes that the project can build on several emerging trends in agriculture. Industry has shown renewed interest in boosting plant growth by manipulating associated microbes (Nature 504, 199; 2013). Companies and farmers are also investing in ‘precision agriculture’, which uses high-tech monitors to track conditions in a field or even around individual plants, allowing farmers to water and fertilize in exactly the right places.

 

High-tech future

 

Eversole foresees a day when tractors will carry dipstick-like gauges that provide a snapshot of the microbial community in the soil. Data from the Phytobiomes Initiative would then help farmers to manipulate that community to their advantage, she says.

 

But first, the initiative needs to standardize protocols and metrics, the meeting’s attendees determined. Kinkel says that efforts are likely to focus initially on cataloguing microbes and insects and their interactions with different crops and habitats. “We’re where plant biologists were 150 years ago,” she says. “We’re still trying to inventory things.”

 

Work has already begun along these lines: for example, a group at the International Rice Research Institute in Los Baños in the Philippines is fishing for microbial DNA in data discarded from an effort to sequence the rice genome. The goal is to determine which microbes prefer which strains of the crop.

 

Kinkel, meanwhile, has begun experimenting with manipulating carbon levels in the soil to alter the microbial population, with the aim of improving plant productivity. “If we can understand better who lives on and within plants, we have the potential to manage them to have healthier, more resilient plants,” she says.

 

Projects such as these would move faster under an organized, cohesive framework, says Sarah Lebeis, a microbiologist at the University of Tennessee in Knoxville who is studying how plants manipulate microbial communities by secreting antibiotics into the soil. “Right now we’re working as individuals,” she says. “Having an initiative will give us focus and hopefully we’ll progress further, faster, better.”


Via Kamoun Lab @ TSL, Jean-Michel Ané
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Front. Plant Sci.: TAL effectors and activation of predicted host targets distinguish Asian from African strains of the rice pathogen Xanthomonas oryzae pv. oryzicola while strict conservation sugg...

Front. Plant Sci.: TAL effectors and activation of predicted host targets distinguish Asian from African strains of the rice pathogen Xanthomonas oryzae pv. oryzicola while strict conservation sugg... | Effectors and Plant Immunity | Scoop.it

Xanthomonas oryzae pv. oryzicola (Xoc) causes the increasingly important disease bacterial leaf streak of rice (BLS) in part by type III delivery of repeat-rich transcription activator-like (TAL) effectors to upregulate host susceptibility genes. By pathogen whole genome, single molecule, real-time sequencing and host RNA sequencing, we compared TAL effector content and rice transcriptional responses across 10 geographically diverse Xoc strains. TAL effector content is surprisingly conserved overall, yet distinguishes Asian from African isolates. Five TAL effectors are conserved across all strains. In a prior laboratory assay in rice cv. Nipponbare, only two contributed to virulence in strain BLS256 but the strict conservation indicates all five may be important, in different rice genotypes or in the field. Concatenated and aligned, TAL effector content across strains largely reflects relationships based on housekeeping genes, suggesting predominantly vertical transmission. Rice transcriptional responses did not reflect these relationships, and on average, only 28% of genes upregulated and 22% of genes downregulated by a strain are up- and downregulated (respectively) by all strains. However, when only known TAL effector targets were considered, the relationships resembled those of the TAL effectors. Toward identifying new targets, we used the TAL effector-DNA recognition code to predict effector binding elements in promoters of genes upregulated by each strain, but found that for every strain, all upregulated genes had at least one. Filtering with a classifier we developed previously decreases the number of predicted binding elements across the genome, suggesting that it may reduce false positives among upregulated genes. Applying this filter and eliminating genes for which upregulation did not strictly correlate with presence of the corresponding TAL effector, we generated testable numbers of candidate targets for four of the five strictly conserved TAL effectors.

 

Wilkins KE, Booher NJ, Wang L and Bogdanove AJ

 

 

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5th Xanthomonas Genomics Conference 2015 - July 8 - 11, 2015. Bogotá, Colombia

5th Xanthomonas Genomics Conference 2015 - July 8 - 11, 2015. Bogotá, Colombia | Effectors and Plant Immunity | Scoop.it

The final program of the XGC 2015... sounds really promising!

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Front. Plant Sci.: Comparative genomics of a cannabis pathogen reveals insight into the evolution of pathogenicity in Xanthomonas (2015)

Front. Plant Sci.: Comparative genomics of a cannabis pathogen reveals insight into the evolution of pathogenicity in Xanthomonas (2015) | Effectors and Plant Immunity | Scoop.it

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

 

Jacobs JM, Pesce C, Lefeuvre P and Koebnik R

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Cell: A Plant Immune Receptor Detects Pathogen Effectors that Target WRKY Transcription Factors (2015)

Cell: A Plant Immune Receptor Detects Pathogen Effectors that Target WRKY Transcription Factors (2015) | Effectors and Plant Immunity | Scoop.it

Defense against pathogens in multicellular eukaryotes depends on intracellular immune receptors, yet surveillance by these receptors is poorly understood. Several plant nucleotide-binding, leucine-rich repeat (NB-LRR) immune receptors carry fusions with other protein domains. The Arabidopsis RRS1-R NB-LRR protein carries a C-terminal WRKY DNA binding domain and forms a receptor complex with RPS4, another NB-LRR protein. This complex detects the bacterial effectors AvrRps4 or PopP2 and then activates defense. Both bacterial proteins interact with the RRS1 WRKY domain, and PopP2 acetylates lysines to block DNA binding. PopP2 and AvrRps4 interact with other WRKY domain-containing proteins, suggesting these effectors interfere with WRKY transcription factor-dependent defense, and RPS4/RRS1 has integrated a “decoy” domain that enables detection of effectors that target WRKY proteins. We propose that NB-LRR receptor pairs, one member of which carries an additional protein domain, enable perception of pathogen effectors whose function is to target that domain.

 

Panagiotis F. Sarris, Zane Duxbury, Sung Un Huh, Yan Ma, Cécile Segonzac, Jan Sklenar, Paul Derbyshire, Volkan Cevik, Ghanasyam Rallapalli, Simon B. Saucet, Lennart Wirthmueller, Frank L.H. Menke, Kee Hoon Sohn, Jonathan D.G. Jones

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Transport of defense compounds from source to sink: lessons learned from glucosinolates: Trends in Plant Science

Transport of defense compounds from source to sink: lessons learned from glucosinolates: Trends in Plant Science | Effectors and Plant Immunity | Scoop.it
Plants synthesize a plethora of defense compounds crucial for their survival in a challenging and changing environment. Transport processes are important for shaping the distribution pattern of defense compounds, albeit focus hitherto has been mostly on their biosynthetic pathways. A recent identification of two glucosinolate transporters represents a breakthrough in our understanding of glucosinolate transport in Arabidopsis and has advanced knowledge in transport of defense compounds. In this review, we discuss the role of the glucosinolate transporters in establishing dynamic glucosinolate distribution patterns and source–sink relations. We focus on lessons learned from glucosinolate transport that may apply to transport of other defense compounds and discuss future avenues in the emerging field of defense compound transport.

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Gene targeting by the TAL effector PthXo2 reveals cryptic resistance gene for bacterial blight of rice - Plant J.

Gene targeting by the TAL effector PthXo2 reveals cryptic resistance gene for bacterial blight of rice - Plant J. | Effectors and Plant Immunity | Scoop.it

(via T. Schreiber, thx)

Bacterial blight of rice is caused by the γ-proteobacterium Xanthomonas oryzae pv. oryzae, which utilizes a group of type III TAL (transcription activator-like) effectors to induce host gene expression and condition host susceptibility. Five SWEET genes are functionally redundant to support bacterial disease, but only two were experimentally proven targets of natural TAL effectors. Here, we report the identification of the sucrose transporter gene OsSWEET13 as the disease susceptibility gene for PthXo2 and the existence of cryptic recessive resistance to PthXo2-dependent X. oryzae pv. oryzae due to promoter variations of OsSWEET13 in japonica rice. PthXo2-containing strains induce OsSWEET13 in indica rice IR24 due to the presence of an unpredicted and undescribed effector binding site not present in the alleles in japonica rice Nipponbare and Kitaake. The specificity of effector-associated gene induction and disease susceptibility is attributable to a single nucleotide polymorphism (SNP), which is also found in a polymorphic allele of OsSWEET13 known as the recessive resistance gene xa25 from the rice cultivar Minghui 63. The mutation of OsSWEET13 with CRISPR/Cas9 technology further corroborates the requirement of OsSWEET13 expression for the state of PthXo2-dependent disease susceptibility to X. oryzae pv. oryzae. Gene profiling of a collection of 104 strains revealed OsSWEET13 induction by 42 isolates of X. oryzae pv. oryzae. Heterologous expression of OsSWEET13 in Nicotiana benthamiana leaf cells elevates sucrose concentrations in the apoplasm. The results corroborate a model whereby X. oryzae pv. oryzae enhances the release of sucrose from host cells in order to exploit the host resources.

 


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J. Exp. Bot.: Identification of a molecular dialogue between developing seeds of Medicago truncatula and seedborne xanthomonads (2015)

J. Exp. Bot.: Identification of a molecular dialogue between developing seeds of Medicago truncatula and seedborne xanthomonads (2015) | Effectors and Plant Immunity | Scoop.it

Plant pathogenic bacteria disseminate and survive mainly in association with seeds. This study addresses whether seeds are passive carriers or engage a molecular dialogue with pathogens during their development. We developed two pathosystems using Medicago truncatula with Xanthomonas alfalfae subsp. alfalfae (Xaa), the natural Medicago sp. pathogen and Xanthomonas campestris pv. campestris (Xcc), a Brassicaceae pathogen. Three days after flower inoculation, the transcriptome of Xcc-infected pods showed activation of an innate immune response that was strongly limited in Xcc mutated in the type three secretion system, demonstrating an incompatible interaction of Xcc with the reproductive structures. In contrast, the presence of Xaa did not result in an activation of defence genes. Transcriptome profiling during development of infected seeds exhibited time-dependent and differential responses to Xcc and Xaa. Gene network analysis revealed that the transcriptome of Xcc-infected seeds was mainly affected during seed filling whereas that of Xaa-infected seeds responded during late maturation. The Xcc-infected seed transcriptome exhibited an activation of defence response and a repression of targeted seed maturation pathways. Fifty-one percent of putative ABSCISIC ACID INSENSITIVE3 targets were deregulated by Xcc, including oleosin, cupin, legumin and chlorophyll degradation genes. At maturity, these seeds displayed decreased weight and increased chlorophyll content. In contrast, these traits were not affected by Xaa infection. These findings demonstrate the existence of a complex molecular dialogue between xanthomonads and developing seeds and provides insights into a previously unexplored trade-off between seed development and pathogen defence.

 

Emmanuel Terrasson, Armelle Darrasse, Karima Righetti, Julia Buitink, David Lalanne, Benoit Ly Vu, Sandra Pelletier, William Bolingue, Marie-Agnès Jacques, and Olivier Leprince

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Front. Plant Sci.: The Xanthomonas effector XopJ triggers a conditional hypersensitive response upon treatment of N. benthamiana leaves with salicylic acid (2015)

Front. Plant Sci.: The Xanthomonas effector XopJ triggers a conditional hypersensitive response upon treatment of N. benthamiana leaves with salicylic acid (2015) | Effectors and Plant Immunity | Scoop.it

XopJ is a Xanthomonas type III effector protein that promotes bacterial virulence on susceptible pepper plants through the inhibition of the host cell proteasome and a resultant suppression of salicylic acid (SA) – dependent defense responses. We show here that Nicotiana benthamiana leaves transiently expressing XopJ display hypersensitive response (HR) –like symptoms when exogenously treated with SA. This apparent avirulence function of XopJ was further dependent on effector myristoylation as well as on an intact catalytic triad, suggesting a requirement of its enzymatic activity for HR-like symptom elicitation. The ability of XopJ to cause a HR-like symptom development upon SA treatment was lost upon silencing of SGT1 and NDR1, respectively, but was independent of EDS1 silencing, suggesting that XopJ is recognized by an R protein of the CC-NBS-LRR class. Furthermore, silencing of NPR1 abolished the elicitation of HR-like symptoms in XopJ expressing leaves after SA application. Measurement of the proteasome activity indicated that proteasome inhibition by XopJ was alleviated in the presence of SA, an effect that was not observed in NPR1 silenced plants. Our results suggest that XopJ - triggered HR-like symptoms are closely related to the virulence function of the effector and that XopJ follows a two-signal model in order to elicit a response in the non-host plant N. benthamiana.

 

Üstün S, Bartetzko V and Börnke F

 

 

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Science: Salicylic acid modulates colonization of the root microbiome by specific bacterial taxa (2015)

Immune systems distinguish “self” from “non-self” to maintain homeostasis and must differentially gate access to allow colonization by potentially beneficial, non-pathogenic microbes. Plant roots grow within extremely diverse soil microbial communities, but assemble a taxonomically limited root-associated microbiome. We grew isogenic Arabidopsis thaliana mutants with altered immune systems in a wild soil and also in recolonization experiments with a synthetic bacterial community. We established that biosynthesis of, and signaling dependent on, the foliar defense phytohormone salicylic acid is required to assemble a normal root microbiome. Salicylic acid modulates colonization of the root by specific bacterial families. Thus, plant immune signaling drives selection from the available microbial communities to sculpt the root microbiome.

 

Sarah L. Lebeis, Sur Herrera Paredes, Derek S. Lundberg, Natalie Breakfield, Jase Gehring, Meredith McDonald, Stephanie Malfatti, Tijana Glavina del Rio, Corbin D. Jones, Susannah G. Tringe, Jeffery L. Dangl

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The Plasmodiophora brassicae genome reveals insights in its life cycle and ancestry of chitin synthases : Scientific Reports : Nature Publishing Group

The Plasmodiophora brassicae genome reveals insights in its life cycle and ancestry of chitin synthases : Scientific Reports : Nature Publishing Group | Effectors and Plant Immunity | Scoop.it

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The ‘prime-ome’: towards a holistic approach to priming

The ‘prime-ome’: towards a holistic approach to priming | Effectors and Plant Immunity | Scoop.it
Plants can be primed to respond faster and more strongly to stress and multiple pathways, specific for the encountered challenge, are involved in priming. This adaptability of priming makes it difficult to pinpoint an exact mechanism: the same phenotypic observation might be the consequence of unrelated underlying events. Recently, details of the molecular aspects of establishing a primed state and its transfer to offspring have come to light. Advances in techniques for detection and quantification of elements spanning the fields of transcriptomics, proteomics, and metabolomics, together with adequate bioinformatics tools, will soon allow us to take a holistic approach to plant defence. This review highlights the state of the art of new strategies to study defence priming in plants and provides perspectives towards ‘prime-omics’.

Via Jean-Michel Ané
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Slides: Plant pathology in the post-genomics era (2015)

Presented at BASF Science Symposium: sustainable food chain - from field to table, Jun 23-24, 2015, Chicago.

 

Notes and acknowledgements at http://kamounlab.tumblr.com/post/122151022390/plant-pathology-in-the-post-genomics-era


Via Kamoun Lab @ TSL
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Front. Plant Sci.: QueTAL: a suite of tools to classify and compare TAL effectors functionally and phylogenetically (2015)

Front. Plant Sci.: QueTAL: a suite of tools to classify and compare TAL effectors functionally and phylogenetically (2015) | Effectors and Plant Immunity | Scoop.it
Transcription Activator-Like (TAL) effectors from Xanthomonas plant pathogenic bacteria can bind to the promoter region of plant genes and induce their expression. DNA-binding specificity is governed by a central domain made of nearly identical repeats, each determining the recognition of one base pair via two amino acid residues (a.k.a. Repeat Variable Di-residue, or RVD). Knowing how TAL effectors differ from each other within and between strains would be useful to infer functional and evolutionary relations, but their repetitive nature precludes reliable use of traditional alignment methods. The suite QueTAL was therefore developed to offer tailored tools for comparison of TAL effector genes. The program DisTAL considers each repeat as a unit, transforms a TAL effector sequence into a sequence of coded repeats and makes pair-wise alignments between these coded sequences to construct trees. The program FuncTAL is aimed at finding TAL effectors with similar DNA-binding capabilities. It calculates correlations between position weight matrices obtained from the RVD sequence, and builds trees based on these correlations. The programs accurately represented phylogenetic and functional relations between TAL effectors using either simulated or literature-curated data. When using the programs on a large set of TAL effector sequences, the DisTAL tree largely reflected the expected species phylogeny. In contrast, FuncTAL showed that TAL effectors with similar binding capabilities can be found between phylogenetically distant taxa. This suite will help users to rapidly analyse any TAL effector genes of interest and compare them to other available TAL genes and should improve our understanding of TAL effectors evolution. It is available at http://bioinfo-web.mpl.ird.fr/cgi-bin2/quetal/quetal.cgi.
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Front. Plant Sci.: MorTAL Kombat: the story of defense against TAL effectors through loss-of-susceptibility (2015)

Front. Plant Sci.: MorTAL Kombat: the story of defense against TAL effectors through loss-of-susceptibility (2015) | Effectors and Plant Immunity | Scoop.it

Many plant-pathogenic xanthomonads rely on Transcription Activator-Like (TAL) effectors to colonize their host. This particular family of type III effectors functions as specific plant transcription factors via a novel programmable DNA-binding domain. Upon binding to the promoters of plant disease susceptibility genes in a sequence-specific manner, the expression of these host genes is induced. However, plants have evolved specific strategies to counter the action of TAL effectors and confer resistance. One mechanism is to avoid the binding of TAL effectors by mutations of their DNA binding sites, resulting in resistance by loss-of-susceptibility. This article reviews our current knowledge of the susceptibility hubs targeted by Xanthomonas TAL effectors, possible evolutionary scenarios for plants to combat the pathogen with loss-of-function alleles, and how this knowledge can be used overall to develop new pathogen-informed breeding strategies and improve crop resistance.

 

Hutin M, Pérez-Quintero AL, Lopez C and Szurek B

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Cell Host Microb.: Pseudomonas syringae pv. tomato DC3000 Type III Secretion Effector Polymutants Reveal an Interplay between HopAD1 and AvrPtoB (2015)

Cell Host Microb.: Pseudomonas syringae pv. tomato DC3000 Type III Secretion Effector Polymutants Reveal an Interplay between HopAD1 and AvrPtoB (2015) | Effectors and Plant Immunity | Scoop.it

The bacterial pathogen Pseudomonas syringae pv. tomato DC3000 suppresses the two-tiered plant innate immune system by injecting a complex repertoire of type III secretion effector (T3E) proteins. Beyond redundancy and interplay, individual T3Es may interact with multiple immunity-associated proteins, rendering their analysis challenging. We constructed a Pst DC3000 polymutant lacking all 36 T3Es and restored individual T3Es or their mutants to explore the interplay among T3Es. The weakly expressed T3E HopAD1 was sufficient to elicit immunity-associated cell death in Nicotiana benthamiana. HopAD1-induced cell death was suppressed partially by native AvrPtoB and completely by AvrPtoBM3, which has mutations disrupting its E3 ubiquitin ligase domain and two known domains for interacting with immunity-associated kinases. AvrPtoBM3 also gained the ability to interact with the immunity-kinase MKK2, which is required for HopAD1-dependent cell death. Thus, AvrPtoB has alternative, competing mechanisms for suppressing effector-triggered plant immunity. This approach allows the deconvolution of individual T3E activities.

 

Hai-Lei Wei, Suma Chakravarthy, Johannes Mathieu, Tyler C. Helmann, Paul Stodghill, Bryan Swingle, Gregory B. Martin, Alan Collmer

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Cell: A Receptor Pair with an Integrated Decoy Converts Pathogen Disabling of Transcription Factors to Immunity (2015)

Cell: A Receptor Pair with an Integrated Decoy Converts Pathogen Disabling of Transcription Factors to Immunity (2015) | Effectors and Plant Immunity | Scoop.it

Microbial pathogens infect host cells by delivering virulence factors (effectors) that interfere with defenses. In plants, intracellular nucleotide-binding/leucine-rich repeat receptors (NLRs) detect specific effector interference and trigger immunity by an unknown mechanism. The Arabidopsis-interacting NLR pair, RRS1-R with RPS4, confers resistance to different pathogens, including Ralstonia solanacearum bacteria expressing the acetyltransferase effector PopP2. We show that PopP2 directly acetylates a key lysine within an additional C-terminal WRKY transcription factor domain of RRS1-R that binds DNA. This disrupts RRS1-R DNA association and activates RPS4-dependent immunity. PopP2 uses the same lysine acetylation strategy to target multiple defense-promoting WRKY transcription factors, causing loss of WRKY-DNA binding and transactivating functions needed for defense gene expression and disease resistance. Thus, RRS1-R integrates an effector target with an NLR complex at the DNA to switch a potent bacterial virulence activity into defense gene activation.

 

Clémentine Le Roux, Gaëlle Huet, Alain Jauneau, Laurent Camborde, Dominique Trémousaygue, Alexandra Kraut, Binbin Zhou, Marie Levaillant, Hiroaki Adachi, Hirofumi Yoshioka, Sylvain Raffaele, Richard Berthomé, Yohann Couté, Jane E. Parker, Laurent Deslandes

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The transmitters: a new blog for people interested in plant-pathogen-vector interactions

The transmitters: a new blog for people interested in plant-pathogen-vector interactions | Effectors and Plant Immunity | Scoop.it

The goal of this blog is to discuss topics relevant to scientists and other parties interested in the vector transmission of plant pathogens, as well as the diseases caused by these pathogens.  This specific field of science is, by definition, multidisciplinary and interdisciplinary; consequently, it is fragmented and very challenging to follow. Here we attempt to bring together colleagues that work on proteomics and ecological modeling, for example, hoping to foment new concepts and ideas, as well as bringing scientists with shared interests closer together.

We are a group of scientists curious about how vectors transmit plant pathogens. We work on the biology, ecology, and evolution of vector-pathogen-plant interactions.  We bring many disciplines, from molecular biology to mathematical modeling, to bear on fundamental and applied questions about the organisms involved in these interactions, as well as on the diseases caused by this group of pathogens.  We also include diverse, international perspectives, and by no means agree on everything, let alone controversial topics in the field. Yet, we still enjoy meeting each other and talking science while sharing a beer, glass of wine, or pastis.

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Front. Microbiol.: Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity (2015)

Front. Microbiol.: Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity (2015) | Effectors and Plant Immunity | Scoop.it

Bacterial spot disease of pepper and tomato is caused by four distinct Xanthomonas species and is a severely limiting factor on fruit yield in these crops. The genetic diversity and the type III effector repertoires of a large sampling of field strains for this disease have yet to be explored on a genomic scale, limiting our understanding of pathogen evolution in an agricultural setting. Genomes of sixty-seven Xanthomonas euvesicatoria (Xe), Xanthomonas perforans (Xp), and Xanthomonas gardneri (Xg) strains isolated from diseased pepper and tomato fields in the southeastern and midwestern United States were sequenced in order to determine the genetic diversity in field strains. Type III effector repertoires were computationally predicted for each strain, and multiple methods of constructing phylogenies were employed to understand better the genetic relationship of strains in the collection. A division in the Xp population was detected based on core genome phylogeny, supporting a model whereby the host-range expansion of Xp field strains on pepper is due, in part, to a loss of the effector AvrBsT. Xp-host compatibility was further studied with the observation that a double deletion mutant of AvrBsT and XopQ in Xp experiences a host gain for Nicotiana benthamiana. Extensive sampling of field strains and an improved understanding of effector content will aid in efforts to design disease resistance strategies targeted against highly conserved core effectors.

 

Schwartz AR, Potnis N, Timilsina S, Wilson M, Patane J, Martins J, Minsavage GV, Dahlbeck D, Akhunova A, Almeida N, Vallad GE, Barak JD, White FF, Miller SA, Ritchie D, Goss E, Bart RS, Setubal JC, Jones JB and Staskawicz BJ

 

 

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#NLR2015 Twitter Archive: NLR BIOLOGY IN PLANTS AND ANIMALS; WORKSHOP AT SCHLOSS RINGBERG; May 2015 DAYS 1/2


Via Kamoun Lab @ TSL
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Front. Plant Sci.: Decision tools for bacterial blight resistance gene deployment in rice-based agricultural ecosystems (2015)

Front. Plant Sci.: Decision tools for bacterial blight resistance gene deployment in rice-based agricultural ecosystems (2015) | Effectors and Plant Immunity | Scoop.it

Attempting to achieve long-lasting and stable resistance using uniformly deployed rice varieties is not a sustainable approach. The real situation appears to be much more complex and dynamic, one in which pathogens quickly adapt to resistant varieties. To prevent disease epidemics, deployment should be customized and this decision will require interdisciplinary actions. This perspective article aims to highlight the current progress on disease resistance deployment to control bacterial blight in rice. Although the model system rice−Xanthomonas oryzae pv. oryzae has distinctive features that underpin the need for a case-by-case analysis, strategies to integrate those elements into a unique decision tool could be easily extended to other crops.

 

Gerbert Sylvestre Dossa, Adam H. Sparks, Casiana Vera Cruz and Ricardo Oliva

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