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A really useful pathogen, Agrobacterium tumefaciens. New Teaching Tool.

A really useful pathogen, Agrobacterium tumefaciens. New Teaching Tool. | Plant-microbe interaction | Scoop.it

The soil bacterium Agrobacterium tumefaciens has a special place in plant biology. Through a rare inter-kingdom DNA transfer, the bacteria move some of their genes into their host's genome, thereby inducing the host cells to proliferate and produce opines, which are nutrients sources for the pathogen. Agrobacterium's ability to transfer DNA makes can be adapted to introduce other genes, such as those encoding useful traits, into plant genomes. The development of Agrobacterium as a tool to transform plants is a landmark event in modern plant biology. This new "Teaching Tool in Plant Biology" provides an introduction to Agrobacterium tumefaciens and related species, focusing on their modes of pathogenicity, their usefulness as tools for plant transformation, and their use as a model for the study of plant-pathogen interactions.

Find it here: http://www.plantcell.org/site/teachingtools/TTPB23.xhtml (subscription to Plant Cell or ASPB membership required).


Via Mary Williams, Nicolas Denancé
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Lidia Pérez de Obanos's curator insight, November 27, 2013 9:15 AM

Agrobacterium tumefaciens es un vector muy útil para muchos tipos de genes que se quieren introducir en distintas plantas. Gracias a ella hemos podido realizar múltiples experimentos y es muy fácil de realizar.

Plant-microbe interaction
Current research on plant immunity, effector proteins, and other inspiring articles
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Frontiers | Interactions of Xanthomonas type-III effector proteins with the plant ubiquitin and ubiquitin-like pathways | Plant-Microbe Interaction

Frontiers | Interactions of Xanthomonas type-III effector proteins with the plant ubiquitin and ubiquitin-like pathways | Plant-Microbe Interaction | Plant-microbe interaction | Scoop.it
In eukaryotes, regulated protein turnover is required during many cellular processes, including defense against pathogens. Ubiquitination and degradation of ubiquitinated proteins via the ubiquitin – proteasome system (UPS) is the main pathway for the turnover of intracellular proteins in eukaryotes. The extensive utilization of the UPS in host cells makes it an ideal pivot for the manipulation of cellular processes by pathogens. Like many other Gram-negative bacteria, Xanthomonas species secrete a suite of type-III effector proteins (T3Es) into their host cells to promote virulence. Some of these T3Es exploit the plant UPS to interfere with immunity. This review summarizes T3E examples from the genus Xanthomonas with a proven or suggested interaction with the host UPS or UPS-like systems and also discusses the apparent paradox that arises from the presence of T3Es that inhibit the UPS in general while others rely on its activity for their function.
Suayib Üstün's insight:

My first Review is online! Also first paper in Frontiers in Plant Science. Next one in this issue is following soon...

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Jennifer Mach's comment, December 3, 2014 8:56 AM
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Molecular and Functional Analyses of a Maize Autoactive NB-LRR Protein Identify Precise Structural Requirements for Activity

Molecular and Functional Analyses of a Maize Autoactive NB-LRR Protein Identify Precise Structural Requirements for Activity | Plant-microbe interaction | Scoop.it
Plant disease resistance is often mediated by nucleotide binding-leucine rich repeat (NLR) proteins which remain auto-inhibited until recognition of specific pathogen-derived molecules causes their activation, triggering a rapid, localized cell death called a hypersensitive response (HR). Three domains are recognized in one of the major classes of NLR proteins: a coiled-coil (CC), a nucleotide binding (NB-ARC) and a leucine rich repeat (LRR) domains. The maize NLR gene Rp1-D21 derives from an intergenic recombination event between two NLR genes, Rp1-D and Rp1-dp2 and confers an autoactive HR. We report systematic structural and functional analyses of Rp1 proteins in maize and N. benthamiana to characterize the molecular mechanism of NLR activation/auto-inhibition. We derive a model comprising the following three main features: Rp1 proteins appear to self-associate to become competent for activity. The CC domain is signaling-competent and is sufficient to induce HR. This can be suppressed by the NB-ARC domain through direct interaction. In autoactive proteins, the interaction of the LRR domain with the NB-ARC domain causes de-repression and thus disrupts the inhibition of HR. Further, we identify specific amino acids and combinations thereof that are important for the auto-inhibition/activity of Rp1 proteins. We also provide evidence for the function of MHD2, a previously uncharacterized, though widely conserved NLR motif. This work reports several novel insights into the precise structural requirement for NLR function and informs efforts towards utilizing these proteins for engineering disease resistance.
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Summer School "PLANT MICROBE INTERACTIONS" @ The Sainsbury Laboratory, 17-28 August 2015, Norwich, UK

Summer School "PLANT MICROBE INTERACTIONS" @ The Sainsbury Laboratory, 17-28 August 2015, Norwich, UK | Plant-microbe interaction | Scoop.it
The last 20 years have provided a sophisticated understanding of how plants recognise relatively conserved microbial patterns to activate defence. In recent years DNA sequencing allowed genomes and transcriptomes of eukaryotic rusts and mildew pathogens to be studied and high-throughput imaging permit the study and visualisation of intracellular interactions during pathogenesis and defence.

 

We will present many aspects of plant- microbe interactions including:

- gene discovery
- genome analysis
- intra-cellular interactions with high-throughput imaging technology
- mechanistic understanding of cellular and molecular processes to translational activities

 

The focus on the dynamic and interactive practical sessions will naturally promote strong interactions between lecturers and participants.


Via Kamoun Lab @ TSL
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Bharat Employment's curator insight, February 25, 1:58 AM

http://www.bharatemployment.com

Jean-Michel Ané's curator insight, February 25, 11:53 AM

That seems an awesome Summer School.

BTW... I want the same chair as Dan MacLean :-)

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TCP transcription factors are critical for the coordinated regulation of ISOCHORISMATE SYNTHASE 1 expression in Arabidopsis thaliana - Wang - The Plant Journal - Wiley Online Library

TCP transcription factors are critical for the coordinated regulation of ISOCHORISMATE SYNTHASE 1 expression in Arabidopsis thaliana - Wang - The Plant Journal - Wiley Online Library | Plant-microbe interaction | Scoop.it
Salicylic acid (SA) plays an important role in various aspects of plant development and response to stresses. To elucidate the sophisticated regulatory mechanism of SA synthesis and signaling, we used a yeast one-hybrid system to screen for regulators of ISOCHORISMATE SYNTHASE 1 (ICS1), a gene encoding the key enzyme in SA biosynthesis in Arabidopsis thaliana. A TEOSINTE-BRANCHED1/ CYCLOIDEA/ PCF (TCP)-family transcription factor AtTCP8 was initially identified as a candidate regulator of ICS1. The regulation of ICS1 by TCP proteins is supported by the presence of a typical TCP binding site in the ICS1 promoter. The binding of TCP8 to this site was further confirmed by in vitro and in vivo assays. Expression patterns of TCP8 and its corresponding gene TCP9 largely overlapped with ICS1 under pathogen attack. A significant reduction in the expression of ICS1 during immune response was observed in tcp8 tcp9 double mutant. We also detected strong interactions between TCP8 and SARD1, WRKY28 or NAC019, as well as among TCP8, TCP9 and TCP20, suggesting a complex coordinated regulatory mechanism underlying ICS1 expression. Our results collectively demonstrate that TCP proteins, with TCP8 and TCP9 being verified as major representatives, are involved in the orchestrated regulation of ICS1 expression.
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The E3 ligase OsPUB15 interacts with the receptor-like kinase PID2 and regulates plant cell death and innate immunity

The E3 ligase OsPUB15 interacts with the receptor-like kinase PID2 and regulates plant cell death and innate immunity | Plant-microbe interaction | Scoop.it
Background

Rice blast disease is one of the most destructive diseases of rice worldwide. We previously cloned the rice blast resistance gene Pid2, which encodes a transmembrane receptor-like kinase containing an extracellular B-lectin domain and an intracellular serine/threonine kinase domain. However, little is known about Pid2-mediated signaling.
Results

Here we report the functional characterization of the U-box/ARM repeat protein OsPUB15 as one of the PID2-binding proteins. We found that OsPUB15 physically interacted with the kinase domain of PID2 (PID2K) in vitro and in vivo and the ARM repeat domain of OsPUB15 was essential for the interaction. In vitro biochemical assays indicated that PID2K possessed kinase activity and was able to phosphorylate OsPUB15. We also found that the phosphorylated form of OsPUB15 possessed E3 ligase activity. Expression pattern analyses revealed that OsPUB15 was constitutively expressed and its encoded protein OsPUB15 was localized in cytosol. Transgenic rice plants over-expressing OsPUB15 at early stage displayed cell death lesions spontaneously in association with a constitutive activation of plant basal defense responses, including excessive accumulation of hydrogen peroxide, up-regulated expression of pathogenesis-related genes and enhanced resistance to blast strains. We also observed that, along with plant growth, the cell death lesions kept spreading over the whole seedlings quickly resulting in a seedling lethal phenotype.
Conclusions

These results reveal that the E3 ligase OsPUB15 interacts directly with the receptor-like kinase PID2 and regulates plant cell death and blast disease resistance.

Via Christophe Jacquet
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Recognition and Activation Domains Contribute to Allele-Specific Responses of an Arabidopsis NLR Receptor to an Oomycete Effector Protein

Recognition and Activation Domains Contribute to Allele-Specific Responses of an Arabidopsis NLR Receptor to an Oomycete Effector Protein | Plant-microbe interaction | Scoop.it
In plants, specific recognition of pathogen effector proteins by nucleotide-binding leucine-rich repeat (NLR) receptors leads to activation of immune responses. RPP1, an NLR from Arabidopsis thaliana, recognizes the effector ATR1, from the oomycete pathogen Hyaloperonospora arabidopsidis, by direct association via C-terminal leucine-rich repeats (LRRs). Two RPP1 alleles, RPP1-NdA and RPP1-WsB, have narrow and broad recognition spectra, respectively, with RPP1-NdA recognizing a subset of the ATR1 variants recognized by RPP1-WsB. In this work, we further characterized direct effector recognition through random mutagenesis of an unrecognized ATR1 allele, ATR1-Cala2, screening for gain-of-recognition phenotypes in a tobacco hypersensitive response assay. We identified ATR1 mutants that a) confirm surface-exposed residues contribute to recognition by RPP1, and b) are recognized by and activate the narrow-spectrum allele RPP1-NdA, but not RPP1-WsB, in co-immunoprecipitation and bacterial growth inhibition assays. Thus, RPP1 alleles have distinct recognition specificities, rather than simply different sensitivity to activation. Using chimeric RPP1 constructs, we showed that RPP1-NdA LRRs were sufficient for allele-specific recognition (association with ATR1), but insufficient for receptor activation in the form of HR. Additional inclusion of the RPP1-NdA ARC2 subdomain, from the central NB-ARC domain, was required for a full range of activation specificity. Thus, cooperation between recognition and activation domains seems to be essential for NLR function.
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The RhoGAP SPIN6 Associates with SPL11 and OsRac1 and Negatively Regulates Programmed Cell Death and Innate Immunity in Rice

The RhoGAP SPIN6 Associates with SPL11 and OsRac1 and Negatively Regulates Programmed Cell Death and Innate Immunity in Rice | Plant-microbe interaction | Scoop.it
The ubiquitin proteasome system in plants plays important roles in plant-microbe interactions and in immune responses to pathogens. We previously demonstrated that the rice U-box E3 ligase SPL11 and its Arabidopsis ortholog PUB13 negatively regulate programmed cell death (PCD) and defense response. However, the components involved in the SPL11/PUB13-mediated PCD and immune signaling pathway remain unknown. In this study, we report that SPL11-interacting Protein 6 (SPIN6) is a Rho GTPase-activating protein (RhoGAP) that interacts with SPL11 in vitro and in vivo. SPL11 ubiquitinates SPIN6 in vitro and degrades SPIN6 in vivo via the 26S proteasome-dependent pathway. Both RNAi silencing in transgenic rice and knockout of Spin6 in a T-DNA insertion mutant lead to PCD and increased resistance to the rice blast pathogen Magnaporthe oryzae and the bacterial blight pathogen Xanthomonas oryzae pv. oryzae. The levels of reactive oxygen species and defense-related gene expression are significantly elevated in both the Spin6 RNAi and mutant plants. Strikingly, SPIN6 interacts with the small GTPase OsRac1, catalyze the GTP-bound OsRac1 into the GDP-bound state in vitro and has GAP activity towards OsRac1 in rice cells. Together, our results demonstrate that the RhoGAP SPIN6 acts as a linkage between a U-box E3 ligase-mediated ubiquitination pathway and a small GTPase-associated defensome system for plant immunity.
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TCP three-way handshake: linking developmental processes with plant immunity: Trends in Plant Science

TCP three-way handshake: linking developmental processes with plant immunity: Trends in Plant Science | Plant-microbe interaction | Scoop.it
Highlights•The roles of TCP factors in plant immunity are discussed.•We shed light on the function of TCP factors in hormonal homeostasis.•We propose a model in which TCP factors are convergent points in the plant immune system.•We discuss the global regulation of TCP proteins at transcriptional and post-transcriptional levels.

The TCP gene family encodes plant-specific transcription factors involved in growth and development. Equally important are the interactions between TCP factors and other pathways extending far beyond development, as they have been found to regulate a variety of hormonal pathways and signaling cascades. Recent advances reveal that TCP factors are targets of pathogenic effectors and are likely to play a vital role in plant immunity. Our focus is on reviewing the involvement of TCP in known pathways and shedding light on other linkages in the nexus of plant immunity centered around TCP factors with an emphasis on the convergence of effectors, interconnected hormonal networks, utility of the circadian clock, and the potential mechanisms by which pathogen defense may occur.

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Perturbation of Maize Phenylpropanoid Metabolism by an AvrE-family Type III Effector from Pantoea stewartii

AvrE-family type III effector proteins share the ability to suppress host defenses, induce disease-associated cell death and promote bacterial growth. However, despite widespread contribution to numerous bacterial diseases in agriculturally important plants, the mode of action of these effectors remains largely unknown. WtsE is an AvrE-family member required for the ability of Pantoea stewartii subsp. stewartii (Pnss) to proliferate efficiently and cause wilt and leaf blight symptoms in maize plants. Notably, when WtsE is delivered by a heterologous system into the leaf cells of susceptible sweet maize seedlings, it alone produces water-soaked disease symptoms reminiscent of those produced by Pnss. Thus, WtsE is a pathogenicity and virulence factor in maize and an Escherichia coli heterologous delivery system can be used to study the activity of WtsE in isolation from other factors produced by Pnss. Transcriptional profiling of maize revealed effects of WtsE, including induction of genes involved in secondary metabolism and suppression of genes involved in photosynthesis. Metabolic profiling revealed that WtsE perturbs maize metabolism, including the induction of coumaroyl tyramine. The ability of mutant WtsE-derivatives to elicit transcriptional and metabolic changes in susceptible maize seedlings correlated with their ability to promote disease. Furthermore, chemical inhibitors that block metabolic flux into the phenylpropanoid pathways targeted by WtsE also disrupted the pathogenicity and virulence activity of WtsE. While numerous metabolites produced downstream of the shikimate pathway are known to promote plant defense, our results indicate that mis-regulated induction of phenylpropanoid metabolism can also be used to promote pathogen virulence.
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Dual roles of an Arabidopsis ESCRT component FREE1 in regulating vacuolar protein transport and autophagic degradation

Dual roles of an Arabidopsis ESCRT component FREE1 in regulating vacuolar protein transport and autophagic degradation | Plant-microbe interaction | Scoop.it
Protein turnover can be achieved via the lysosome/vacuole and the autophagic degradation pathways. Evidence has accumulated revealing that efficient autophagic degradation requires functional endosomal sorting complex required for transport (ESCRT) machinery. However, the interplay between the ESCRT machinery and the autophagy regulator remains unclear. Here, we show that FYVE domain protein required for endosomal sorting 1 (FREE1), a recently identified plant-specific ESCRT component essential for multivesicular body (MVB) biogenesis and plant growth, plays roles both in vacuolar protein transport and autophagic degradation. FREE1 also regulates vacuole biogenesis in both seeds and vegetative cells of Arabidopsis. Additionally, FREE1 interacts directly with a unique plant autophagy regulator SH3 DOMAIN-CONTAINING PROTEIN2 and associates with the PI3K complex, to regulate the autophagic degradation in plants. Thus, FREE1 plays multiple functional roles in vacuolar protein trafficking and organelle biogenesis as well as in autophagic degradation via a previously unidentified regulatory mechanism of cross-talk between the ESCRT machinery and autophagy process.
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c-Abl Regulates Proteasome Abundance by Controlling the Ubiquitin-Proteasomal Degradation of PSMA7 Subunit: Cell Reports

c-Abl Regulates Proteasome Abundance by Controlling the Ubiquitin-Proteasomal Degradation of PSMA7 Subunit: Cell Reports | Plant-microbe interaction | Scoop.it
The ubiquitin-proteasome system is a vital proteolytic pathway required for cell homeostasis. However, the turnover mechanism of the proteasome subunit itself is still not understood. Here, we show that the 20S proteasome subunit PSMA7 is subjected to ubiquitination and proteasomal degradation, which was suppressed by PSMA7 phosphorylation at Y106 mediated by the nonreceptor tyrosine kinases c-Abl/Arg. BRCA1 specifically functions as an E3 ubiquitin ligase of PSMA7 ubiquitination. c-Abl/Arg regulates cellular proteasome abundance by controlling the PSMA7 subunit supply. Downregulated PSMA7 level results in decreased proteasome abundance in c-Abl/Arg RNAi-knockdown or c-abl/arg-deficient cells, which demonstrated an increased sensitivity to proteasome inhibition. In response to oxidative stress, the c-Abl-mediated upregulation of proteasome level compensates for the proteasomal activity impairment induced by reactive oxygen species. Abl-kinases-regulated biogenesis and homeostasis of proteasome complexes may be important for understanding related diseases and pathological states.
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A Truncated NLR Protein, TIR-NBS2, Is Required for Activated Defense Responses in the exo70B1 Mutant

A Truncated NLR Protein, TIR-NBS2, Is Required for Activated Defense Responses in the exo70B1 Mutant | Plant-microbe interaction | Scoop.it

Abstract

 

During exocytosis, the evolutionarily conserved exocyst complex tethers Golgi-derived vesicles to the target plasma membrane, a critical function for secretory pathways. Here we show that exo70B1 loss-of-function mutants express activated defense responses upon infection and express enhanced resistance to fungal, oomycete and bacterial pathogens. In a screen for mutants that suppress exo70B1 resistance, we identified nine alleles of TIR-NBS2 (TN2), suggesting that loss-of-function of EXO70B1 leads to activation of this nucleotide binding domain and leucine-rich repeat-containing (NLR)-like disease resistance protein. This NLR-like protein is atypical because it lacks the LRR domain common in typical NLR receptors. In addition, we show that TN2 interacts with EXO70B1 in yeast and in planta. Our study thus provides a link between the exocyst complex and the function of a ‘TIR-NBS only’ immune receptor like protein. Our data are consistent with a speculative model wherein pathogen effectors could evolve to target EXO70B1 to manipulate plant secretion machinery. TN2 could monitor EXO70B1 integrity as part of an immune receptor complex.

Author Summary

Secretory pathways play an important role in the plant immune response by delivering antimicrobial compounds and metabolites to the site of infection. The evolutionarily conserved exocyst complex is involved in exocytosis, the final step in the secretory pathway. We showed that loss of the function of EXO70B1, a subunit of exocyst complex, results in activated defense responses, and enhanced resistance to a range of pathogens. We found that EXO70B1 associates with the SNARE complex protein SNAP33, which is involved in focal secretion of defense-related proteins. Enhanced disease resistance and cell death in the exo70B1 mutant are dependent on TIR-NBS2 (TN2), an atypical intracellular immune receptor-like protein that lacks leucine-rich repeats. TN2 physically associates with EXO70B1, and TN2 transcripts accumulate at much higher levels in the exo70B1 mutant. These data are consistent with a model where activation of a receptor pathway containing TIR-NBS2 is responsible for activated defense responses and cell death in exo70B1. Our data further suggest that this, and possibly other, exocyst components could be targets of effectors that are guarded by immune receptors.

 

 


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The Arabidopsis Transcription Factor BES1 Is a Direct Substrate of MPK6 and Regulates Immunity

Pathogen-associated molecular patterns (PAMPs) are recognized by plant pattern-recognition receptors (PRRs) to activate PAMP-triggered immunity (PTI). Mitogen-activated protein kinases (MAPKs), as well as other cytoplasmic kinases, integrate upstream immune signals, and in turn dissect PTI signaling via different substrates to regulate defense responses. However, only a few direct substrates of these signaling kinases have been identified. Here we show that PAMP perception enhances phosphorylation of BES1 (BRI1-EMS suppressor 1), a transcription factor involved in brassinosteroid (BR) signaling pathway, through pathogen-induced MAPKs in Arabidopsis. BES1 interacts with MPK6 (MAP kinase 6), and is phosphorylated by MPK6. bes1 loss-of-function mutants display compromised resistance to bacterial pathogen Pseudomonas syringae pv. tomato DC3000. BES1SSAA (BES1 S286A/S137A double mutation) impairs PAMP-induced phosphorylation and fails to restore bacterial resistance in bes1 mutant, indicating a positive role of BES1 phosphorylation in plant immunity. BES1 is phosphorylated by glycogen synthase kinase-3 (GSK3)-like kinase BIN2 (BR insensitive 2), a negative regulator of BR signaling. BR perception inhibits BIN2 activity, allowing dephosphorylation of BES1 to regulate plant development. However, BES1SSAA does not affect BR-mediated plant growth, suggesting differential residue requirements for the modulation of BES1 phosphorylation in PTI and BR signaling. Our study identifies BES1 as a novel direct substrate of MPK6 in PTI signaling. This finding reveals MAPK-mediated BES1 phosphorylation as another BES1 modulation mechanism in plant cell signaling, in addition to GSK3-like kinase-mediated BES1 phosphorylation and F box protein-mediated BES1 degradation.
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Plants and Pathogens teaching tool updated and revised

Plants and Pathogens teaching tool updated and revised | Plant-microbe interaction | Scoop.it

We've updated and revised TTPB22, "Plants and Pathogens". http://www.plantcell.org/site/teachingtools/TTPB22.xhtml
Lots and lots of new references, a few new case studies and some new slides too. What a fascinating and wonderful topic to have a chance to revisit!


Via Mary Williams
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The receptor-like cytoplasmic kinase PCRK1 contributes to pattern-triggered immunity against Pseudomonas syringae in Arabidopsis thaliana - Sreekanta - 2015 - New Phytologist - Wiley Online Library

The receptor-like cytoplasmic kinase PCRK1 contributes to pattern-triggered immunity against Pseudomonas syringae in Arabidopsis thaliana - Sreekanta - 2015 - New Phytologist - Wiley Online Library | Plant-microbe interaction | Scoop.it
In this paper we describe PATTERN-TRIGGERED IMMUNITY (PTI) COMPROMISED RECEPTOR-LIKE CYTOPLASMIC KINASE 1 (PCRK1) of Arabidopsis thaliana, an RLCK that is important for defense against the pathogen Pseudomonas syringae pv. maculicola ES4326 (Pma ES4326).
We examined defense responses such as bacterial growth, production of reactive oxygen species (ROS) and callose deposition in pcrk1 mutant plants to determine the role of PCRK1 during pathogen infection.
Expression of PCRK1 was induced following pathogen infection. Pathogen growth was significantly higher in pcrk1 mutant lines than in wild-type Col-0. Mutant pcrk1 plants showed reduced pattern-triggered immunity (PTI) against Pma ES4326 after pretreatment with peptides derived from flagellin (flg22), elongation factor-Tu (elf18), or an endogenous protein (pep1). Deposition of callose was reduced in pcrk1 plants, indicating a role of PCRK1 in activation of early immune responses. A PCRK1 transgene containing a mutation in a conserved lysine residue important for phosphorylation activity of kinases (K118E) failed to complement a pcrk1 mutant for the Pma ES4326 growth phenotype.
Our study shows that PCRK1 plays an important role during PTI and that a conserved lysine residue in the putative kinase domain is important for PCRK1 function.
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NIK1-mediated translation suppression functions as a plant antiviral immunity mechanism : Nature : Nature Publishing Group

NIK1-mediated translation suppression functions as a plant antiviral immunity mechanism : Nature : Nature Publishing Group | Plant-microbe interaction | Scoop.it
Plants and plant pathogens are subject to continuous co-evolutionary pressure for dominance, and the outcomes of these interactions can substantially impact agriculture and food security1, 2, 3. In virus–plant interactions, one of the major mechanisms for plant antiviral immunity relies on RNA silencing, which is often suppressed by co-evolving virus suppressors, thus enhancing viral pathogenicity in susceptible hosts1. In addition, plants use the nucleotide-binding and leucine-rich repeat (NB-LRR) domain-containing resistance proteins, which recognize viral effectors to activate effector-triggered immunity in a defence mechanism similar to that employed in non-viral infections2, 3. Unlike most eukaryotic organisms, plants are not known to activate mechanisms of host global translation suppression to fight viruses1, 2. Here we demonstrate in Arabidopsis that the constitutive activation of NIK1, a leucine-rich repeat receptor-like kinase (LRR-RLK) identified as a virulence target of the begomovirus nuclear shuttle protein (NSP)4, 5, 6, leads to global translation suppression and translocation of the downstream component RPL10 to the nucleus, where it interacts with a newly identified MYB-like protein, L10-INTERACTING MYB DOMAIN-CONTAINING PROTEIN (LIMYB), to downregulate translational machinery genes fully. LIMYB overexpression represses ribosomal protein genes at the transcriptional level, resulting in protein synthesis inhibition, decreased viral messenger RNA association with polysome fractions and enhanced tolerance to begomovirus. By contrast, the loss of LIMYB function releases the repression of translation-related genes and increases susceptibility to virus infection. Therefore, LIMYB links immune receptor LRR-RLK activation to global translation suppression as an antiviral immunity strategy in plants.
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5th Xanthomonas Genomics Conference, July 8 - 11, 2015, Bogotá, Colombia

5th Xanthomonas Genomics Conference, July 8 - 11, 2015, Bogotá, Colombia | Plant-microbe interaction | Scoop.it

Via Kamoun Lab @ TSL
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Retromer Contributes to Immunity-Associated Cell Death in Arabidopsis

Retromer Contributes to Immunity-Associated Cell Death in Arabidopsis | Plant-microbe interaction | Scoop.it
Membrane trafficking is required during plant immune responses, but its contribution to the hypersensitive response (HR), a form of programmed cell death (PCD) associated with effector-triggered immunity, is not well understood. HR is induced by nucleotide binding-leucine-rich repeat (NB-LRR) immune receptors and can involve vacuole-mediated processes, including autophagy. We previously isolated lazarus (laz) suppressors of autoimmunity-triggered PCD in the Arabidopsis thaliana mutant accelerated cell death11 (acd11) and demonstrated that the cell death phenotype is due to ectopic activation of the LAZ5 NB-LRR. We report here that laz4 is mutated in one of three VACUOLAR PROTEIN SORTING35 (VPS35) genes. We verify that LAZ4/VPS35B is part of the retromer complex, which functions in endosomal protein sorting and vacuolar trafficking. We show that VPS35B acts in an endosomal trafficking pathway and plays a role in LAZ5-dependent acd11 cell death. Furthermore, we find that VPS35 homologs contribute to certain forms of NB-LRR protein-mediated autoimmunity as well as pathogen-triggered HR. Finally, we demonstrate that retromer deficiency causes defects in late endocytic/lytic compartments and impairs autophagy-associated vacuolar processes. Our findings indicate important roles of retromer-mediated trafficking during the HR; these may include endosomal sorting of immune components and targeting of vacuolar cargo.
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Arabidopsis HFR1 Is a Potential Nuclear Substrate Regulated by the Xanthomonas Type III Effector XopD Xcc 8004

Arabidopsis  HFR1 Is a Potential Nuclear Substrate Regulated by the  Xanthomonas  Type III Effector XopD  Xcc 8004 | Plant-microbe interaction | Scoop.it

XopDXcc8004, a type III effector of Xanthomonas campestris pv. campestris (Xcc) 8004, is considered a shorter version of the XopD, which lacks the N-terminal domain. To understand the functions of XopDXcc8004, in planta, a transgenic approach combined with inducible promoter to analyze the effects of XopDXcc8004 in Arabidopsis was done. Here, the expression of XopDXcc8004, in Arabidopsis elicited the accumulation of host defense-response genes. These molecular changes were dependent on salicylic acid and correlated with lesion-mimic phenotypes observed in XVE::XopDXcc8004 transgenic plants. Moreover, XopDXcc8004 was able to desumoylate HFR1, a basic helix-loop-helix transcription factor involved in photomorphogenesis, through SUMO protease activity. Interestingly, the hfr1-201 mutant increased the expression of host defense-response genes and displayed a resistance phenotype to Xcc8004. These data suggest that HFR1 is involved in plant innate immunity and is potentially regulated by XopDXcc8004.

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The mRNA decay factor PAT1 functions in a pathway including MAP kinase 4 and immune receptor SUMM2 - Roux - 2015 - The EMBO Journal - Wiley Online Library

The mRNA decay factor PAT1 functions in a pathway including MAP kinase 4 and immune receptor SUMM2 - Roux - 2015 - The EMBO Journal - Wiley Online Library | Plant-microbe interaction | Scoop.it

Multi-layered defense responses are activated in plants upon recognition of invading pathogens. Transmembrane receptors recognize conserved pathogen-associated molecular patterns (PAMPs) and activate MAP kinase cascades, which regulate changes in gene expression to produce appropriate immune responses. For example, Arabidopsis MAP kinase 4 (MPK4) regulates the expression of a subset of defense genes via at least one WRKY transcription factor. We report here that MPK4 is found in complexes in vivo with PAT1, a component of the mRNA decapping machinery. PAT1 is also phosphorylated by MPK4 and, upon flagellin PAMP treatment, PAT1 accumulates and localizes to cytoplasmic processing (P) bodies which are sites for mRNA decay. Pat1 mutants exhibit dwarfism and de-repressed immunity dependent on the immune receptor SUMM2. Since mRNA decapping is a critical step in mRNA turnover, linking MPK4 to mRNA decay via PAT1 provides another mechanism by which MPK4 may rapidly instigate immune responses.

 

Synopsis


The identification of mRNA decapping factor PAT1 as a new target for MAP kinase 4 offers insight on the emerging connection between RNA metabolism and immunity in plants.

- Eukaryotic PAT1 proteins are key components in post-transcriptional regulation of gene expression
- Arabidopsis PAT1 functions in decapping and is a substrate of MAP kinase 4 which regulates immune responses in a PAMP-triggered pathway associated with the immune receptor SUMM2
- PAT1 accumulates in processing (P) bodies upon PAMP treatment
- PAT1 interacts with the resistance protein SUMM2 and pat1 mutants exhibit SUMM2-dependent autoimmunity in Arabidopsis

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Recruitment of PLANT U-BOX13 and the PI4Kβ1/β2 Phosphatidylinositol-4 Kinases by the Small GTPase RabA4B Plays Important Roles during Salicylic Acid-Mediated Plant Defense Signaling in Arabidopsis

Recruitment of PLANT U-BOX13 and the PI4Kβ1/β2 Phosphatidylinositol-4 Kinases by the Small GTPase RabA4B Plays Important Roles during Salicylic Acid-Mediated Plant Defense Signaling in Arabidopsis | Plant-microbe interaction | Scoop.it
Protection against microbial pathogens involves the activation of cellular immune responses in eukaryotes, and this cellular immunity likely involves changes in subcellular membrane trafficking. In eukaryotes, members of the Rab GTPase family of small monomeric regulatory GTPases play prominent roles in the regulation of membrane trafficking. We previously showed that RabA4B is recruited to vesicles that emerge from trans-Golgi network (TGN) compartments and regulates polarized membrane trafficking in plant cells. As part of this regulation, RabA4B recruits the closely related phosphatidylinositol 4-kinase (PI4K) PI4Kβ1 and PI4Kβ2 lipid kinases. Here, we identify a second Arabidopsis thaliana RabA4B-interacting protein, PLANT U-BOX13 (PUB13), which has recently been identified to play important roles in salicylic acid (SA)-mediated defense signaling. We show that PUB13 interacts with RabA4B through N-terminal domains and with phosphatidylinositol 4-phosphate (PI-4P) through a C-terminal armadillo domain. Furthermore, we demonstrate that a functional fluorescent PUB13 fusion protein (YFP-PUB13) localizes to TGN and Golgi compartments and that PUB13, PI4Kβ1, and PI4Kβ2 are negative regulators of SA-mediated induction of pathogenesis-related gene expression. Taken together, these results highlight a role for RabA4B and PI-4P in SA-dependent defense responses.
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Transcriptional networks in plant immunity - Tsuda - 2015 - New Phytologist - Wiley Online Library

Transcriptional networks in plant immunity - Tsuda - 2015 - New Phytologist - Wiley Online Library | Plant-microbe interaction | Scoop.it
Next to numerous abiotic stresses, plants are constantly exposed to a variety of pathogens within their environment. Thus, their ability to survive and prosper during the course of evolution was strongly dependent on adapting efficient strategies to perceive and to respond to such potential threats. It is therefore not surprising that modern plants have a highly sophisticated immune repertoire consisting of diverse signal perception and intracellular signaling pathways. This signaling network is intricate and deeply interconnected, probably reflecting the diverse lifestyles and infection strategies used by the multitude of invading phytopathogens. Moreover it allows signal communication between developmental and defense programs thereby ensuring that plant growth and fitness are not significantly retarded. How plants integrate and prioritize the incoming signals and how this information is transduced to enable appropriate immune responses is currently a major research area. An important finding has been that pathogen-triggered cellular responses involve massive transcriptional reprogramming within the host. Additional key observations emerging from such studies are that transcription factors (TFs) are often sites of signal convergence and that signal-regulated TFs act in concert with other context-specific TFs and transcriptional co-regulators to establish sensory transcription regulatory networks required for plant immunity.
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Regulation of Specialized Metabolism by WRKY Transcription Factors

Regulation of Specialized Metabolism by WRKY Transcription Factors | Plant-microbe interaction | Scoop.it

WRKY transcription factors (TFs) are well known for regulating plant abiotic and biotic stress tolerance. However, much less is known about how WRKY TFs affect plant-specialized metabolism. Analysis of WRKY TFs regulating the production of specialized metabolites emphasizes the values of the family outside of traditionally accepted roles in stress tolerance. WRKYs with conserved roles across plant species seem to be essential in regulating specialized metabolism. Overall, the WRKY family plays an essential role in regulating the biosynthesis of important pharmaceutical, aromatherapy, biofuel, and industrial components, warranting considerable attention in the forthcoming years.

 

 


Via Christophe Jacquet, Mary Williams, Jennifer Mach
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Exp Botany: The NPR1-dependent salicylic acid signalling pathway is pivotal for enhanced salt and oxidative stress tolerance in Arabidopsis

Exp Botany: The NPR1-dependent salicylic acid signalling pathway is pivotal for enhanced salt and oxidative stress tolerance in Arabidopsis | Plant-microbe interaction | Scoop.it
The role of endogenous salicylic acid (SA) signalling cascades in plant responses to salt and oxidative stresses is unclear. Arabidopsis SA signalling mutants, namely npr1-5 (non-expresser of pathogenesis related gene1), which lacks NPR1-dependent SA signalling, and nudt7 (nudix hydrolase7), which has both constitutively expressed NPR1-dependent and NPR1-independent SA signalling pathways, were compared with the wild type (Col-0) during salt or oxidative stresses. Growth and viability staining showed that, compared with wild type, the npr1-5 mutant was sensitive to either salt or oxidative stress, whereas the nudt7 mutant was tolerant. Acute salt stress caused the strongest membrane potential depolarization, highest sodium and proton influx, and potassium loss from npr1-5 roots in comparison with the wild type and nudt7 mutant. Though salt stress-induced hydrogen peroxide production was lowest in the npr1-5 mutant, the reactive oxygen species (ROS) stress (induced by 1mM of hydroxyl-radical-generating copper-ascorbate mix, or either 1 or 10mM hydrogen peroxide) caused a higher potassium loss from the roots of the npr1-5 mutant than the wild type and nudt7 mutant. Long-term salt exposure resulted in the highest sodium and the lowest potassium concentration in the shoots of npr1-5 mutant in comparison with the wild type and nudt7 mutant. The above results demonstrate that NPR1-dependent SA signalling is pivotal to (i) controlling Na+ entry into the root tissue and its subsequent long-distance transport into the shoot, and (ii) preventing a potassium loss through depolarization-activated outward-rectifying potassium and ROS-activated non-selective cation channels. In conclusion, NPR1-dependent SA signalling is central to the salt and oxidative stress tolerance in Arabidopsis.

Via Christophe Jacquet, Jim Alfano
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Internalization and vacuolar targeting of the brassinosteroid hormone receptor BRI1 are regulated by ubiquitination : Nature Communications : Nature Publishing Group

Internalization and vacuolar targeting of the brassinosteroid hormone receptor BRI1 are regulated by ubiquitination : Nature Communications : Nature Publishing Group | Plant-microbe interaction | Scoop.it
Brassinosteroids are plant steroid hormones that control many aspects of plant growth and development, and are perceived at the cell surface by the plasma membrane-localized receptor kinase BRI1. Here we show that BRI1 is post-translationally modified by K63 polyubiquitin chains in vivo. Using both artificial ubiquitination of BRI1 and generation of an ubiquitination-defective BRI1 mutant form, we demonstrate that ubiquitination promotes BRI1 internalization from the cell surface and is essential for its recognition at the trans-Golgi network/early endosomes (TGN/EE) for vacuolar targeting. Finally, we demonstrate that the control of BRI1 protein dynamics by ubiquitination is an important control mechanism for brassinosteroid responses in plants. Altogether, our results identify ubiquitination and K63-linked polyubiquitin chain formation as a dual targeting signal for BRI1 internalization and sorting along the endocytic pathway, and highlight its role in hormonally controlled plant development.
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The Phylogenetically-Related Pattern Recognition Receptors EFR and XA21 Recruit Similar Immune Signaling Components in Monocots and Dicots

The Phylogenetically-Related Pattern Recognition Receptors EFR and XA21 Recruit Similar Immune Signaling Components in Monocots and Dicots | Plant-microbe interaction | Scoop.it
Author Summary Pests and diseases cause significant agricultural losses. Plants recognize pathogen-derived molecules via plasma membrane-localized immune receptors (called pattern recognition receptors or PRRs), resulting in pathogen resistance. In recent years, the transfer of PRRs across plant species has emerged as a promising biotechnological approach to improve crop disease resistance. Successful transfers of PRRs suggest that immune signaling components are conserved across plant specie
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