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Science (2012): Natural Enemies Drive Geographic Variation in Plant Defenses

Science (2012): Natural Enemies Drive Geographic Variation in Plant Defenses | Plant-microbe interaction | Scoop.it

Plants defend themselves against attack by natural enemies, and these defenses vary widely across populations. However, whether communities of natural enemies are a sufficiently potent force to maintain polymorphisms in defensive traits is largely unknown. Here, we exploit the genetic resources of Arabidopsis thaliana, coupled with 39 years of field data on aphid abundance, to (i) demonstrate that geographic patterns in a polymorphic defense locus (GS-ELONG) are strongly correlated with changes in the relative abundance of two specialist aphids; and (ii) demonstrate differential selection by the two aphids on GS-ELONG, using a multigeneration selection experiment. We thereby show a causal link between variation in abundance of the two specialist aphids and the geographic pattern at GS-ELONG, which highlights the potency of natural enemies as selective forces.

 

Tobias Züst, Christian Heichinger, Ueli Grossniklaus, Richard Harrington, Daniel J. Kliebenstein, Lindsay A. Turnbull


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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.
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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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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.

 

 


Via Christophe Jacquet
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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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Structural basis for the facilitative diffusion mechanism by SemiSWEET transporter : Nature Communications : Nature Publishing Group

Structural basis for the facilitative diffusion mechanism by SemiSWEET transporter : Nature Communications : Nature Publishing Group | Plant-microbe interaction | Scoop.it

SWEET family proteins mediate sugar transport across biological membranes and play crucial roles in plants and animals. The SWEETs and their bacterial homologues, the SemiSWEETs, are related to the PQ-loop family, which is characterized by highly conserved proline and glutamine residues (PQ-loop motif). Although the structures of the bacterial SemiSWEETs were recently reported, the conformational transition and the significance of the conserved motif in the transport cycle have remained elusive. Here we report crystal structures of SemiSWEET from Escherichia coli, in the both inward-open and outward-open states. A structural comparison revealed that SemiSWEET undergoes an intramolecular conformational change in each protomer. The conserved PQ-loop motif serves as a molecular hinge that enables the ‘binder clip-like’ motion of SemiSWEET. The present work provides the framework for understanding the overall transport cycles of SWEET and PQ-loop family proteins.

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SEB Prague 2015: Plant Biology Sessions, June 30-July 3

SEB Prague 2015: Plant Biology Sessions, June 30-July 3 | Plant-microbe interaction | Scoop.it

In nature plants are colonised by beneficial and pathogenic microbes. While plants benefit from the interactions with beneficial microbes (mutualists), pathogenic microbes cause diseases and arrest plant growth. Both mutualistic and pathogenic microbes are initially confronted with a highly effective immune system, which they have to overcome in order to colonise their hosts. Hence, despite the different outcomes of mutualistic and pathogenic interactions, both microbial groups face the same hurdles to establish their accommodation in the plant. A plethora of recent studies indicated that mutualists and pathogens secrete effectors, mainly proteins but also small interfering RNAs, with the purpose not only to manipulate host immunity but also to modify host metabolism in order to create an environment suitable for microbial reproduction.

 

The session will highlight the current knowledge of how mutualistic and pathogenic microbes employ effectors to successfully establish their respective interactions with plants. The aim is to bring together a group of experts in plant microbe interactions to identify commonalities and discrepancies in the mode of action of mutualistic and pathogenic effectors. Improving our understanding of effector biology will enable us to uncover the molecular principles governing mutualism and disease outbreaks and to synergistically apply this knowledge to sustainably enhance stress adaptation in crops.


Via Kamoun Lab @ TSL
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A Ralstonia solanacearum Type III Effector Directs the Production of the Plant Signal Metabolite Trehalose-6-Phosphate

A Ralstonia solanacearum Type III Effector Directs the Production of the Plant Signal Metabolite Trehalose-6-Phosphate | Plant-microbe interaction | Scoop.it
The plant pathogen Ralstonia solanacearum possesses two genes encoding a trehalose-6-phosphate synthase (TPS), an enzyme of the trehalose biosynthetic pathway. One of these genes, named ripTPS, was found to encode a protein with an additional N-terminal domain which directs its translocation into host plant cells through the type 3 secretion system. RipTPS is a conserved effector in the R. solanacearum species complex, and homologues were also detected in other bacterial plant pathogens. Functional analysis of RipTPS demonstrated that this type 3 effector synthesizes trehalose-6-phosphate and identified residues essential for this enzymatic activity. Although trehalose-6-phosphate is a key signal molecule in plants that regulates sugar status and carbon assimilation, the disruption of ripTPS did not alter the virulence of R. solanacearum on plants. However, heterologous expression assays showed that this effector specifically elicits a hypersensitive-like response on tobacco that is independent of its enzymatic activity and is triggered by the C-terminal half of the protein. Recognition of this effector by the plant immune system is suggestive of a role during the infectious process.
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bioRxiv: Phytophthora infestans RXLR-WY effector AVR3a associates with a Dynamin-Related Protein involved in endocytosis of a plant pattern recognition receptor (2014)

bioRxiv: Phytophthora infestans RXLR-WY effector AVR3a associates with a Dynamin-Related Protein involved in endocytosis of a plant pattern recognition receptor (2014) | Plant-microbe interaction | Scoop.it

Perception of pathogen associated molecular patterns (PAMPs) by cell surface localized pattern recognition receptors (PPRs), activates plant basal defense responses in a process known as PAMP/PRR–triggered immunity (PTI). In turn, pathogens deploy effector proteins that interfere with different steps in PTI signaling. However, our knowledge of PTI suppression by filamentous plant pathogens, i.e. fungi and oomycetes, remains fragmentary. Previous work revealed that BAK1/SERK3, a regulatory receptor of several PRRs, contributes to basal immunity against the Irish potato famine pathogen Phytophthora infestans. Moreover BAK1/SERK3 is required for the cell death induced by P. infestans elicitin INF1, a protein with characteristics of PAMPs. The P. infestans host-translocated RXLR-WY effector AVR3a is known to supress INF1-mediated defense by binding the E3 ligase CMPG1. In contrast, AVR3aKI-Y147del, a deletion mutant of the C-terminal tyrosine of AVR3a, fails to bind CMPG1 and suppress INF1 cell death. Here we studied the extent to which AVR3a and its variants perturb additional BAK1/SERK3 dependent PTI responses using the plant PRR FLAGELLIN SENSING 2 (FLS2). We found that all tested variants of AVR3a, including AVR3aKI-Y147del, suppress early defense responses triggered by the bacterial flagellin-derived peptide flg22 and reduce internalization of activated FLS2 from the plasma membrane without disturbing its nonactivated localization. Consistent with this effect of AVR3a on FLS2 endocytosis, we discovered that AVR3a associates with the Dynamin-Related Protein DRP2, a plant GTPase implicated in receptor-mediated endocytosis. Interestingly, DRP2 is required for ligand-induced FLS2 internalization but does not affect internalization of the growth receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1). Furthermore, overexpression of DRP2 suppressed accumulation of reactive oxygen species triggered by PAMP treatment. We conclude that AVR3a associates with a key cellular trafficking and membrane-remodeling complex involved in immune receptor-mediated endocytosis and signaling. AVR3a is a multifunctional effector that can suppress BAK1/SERK3 mediated immunity through at least two different pathways.


Via Kamoun Lab @ TSL
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fundoshi's curator insight, December 22, 2014 3:10 AM
Arabidopsis dynamin-related proteins, DRP2A and DRP2B, function coordinately in post-Golgi trafficking.

http://www.sciencedirect.com/science/article/pii/S0006291X14020956

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Domain Dissection of AvrRxo1 for Suppressor, Avirulence and Cytotoxicity Functions

Domain Dissection of AvrRxo1 for Suppressor, Avirulence and Cytotoxicity Functions | Plant-microbe interaction | Scoop.it
AvrRxo1, a type III effector from Xanthomonas oryzae pv. oryzicola (Xoc) which causes bacterial leaf streak (BLS) in rice, can be recognised by non-host resistance protein Rxo1. It triggers a hypersensitive response (HR) in maize. Little is known regarding the virulence function of AvrRxo1. In this study, we determined that AvrRxo1 is able to suppress the HR caused by the non-host resistance recognition of Xanthomonas oryzae pv. oryzae (Xoo) by Nicotiana benthamiana. It is toxic, inducing cell death from transient expression in N. benthamiana, as well as in yeast. Among the four AvrRxo1 alleles from different Xoc strains, we concluded that the toxicity is abolished by a single amino acid substitution at residue 344 in two AvrRxo1 alleles. A series of truncations from the carboxyl terminus (C-terminus) indicate that the complete C-terminus of AvrRxo1 plays an essential role as a suppressor or cytotoxic protein. The C-terminus was also required for the avirulence function, but the last two residues were not necessary. The first 52 amino acids of N-terminus are unessential for toxicity. Point mutagenesis experiments indicate that the ATP/GTP binding site motif A is required for all three functions of AvrRxo1, and NLS is required for both the avirulence and the suppression of non-host resistance. The putative thiol protease site is only required for the cytotoxicity function. These results determine that AvrRxo1 plays a role in the complex interaction with host proteins after delivery into plant cells.
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36th New Phytologist Symposium: Cell biology at the plant–microbe interface, Munich, Germany 29 Nov – 1 Dec 2015

36th New Phytologist Symposium: Cell biology at the plant–microbe interface, Munich, Germany 29 Nov – 1 Dec 2015 | Plant-microbe interaction | Scoop.it

Symposium aim - We aim to organize a cutting edge meeting focused on the application of cell biology approaches to understand the mechanisms that diverse microbes use to manipulate plant cells to benefit their life styles. The meeting will bring together researchers working on a broad spectrum of microbes across different taxa (bacteria, fungi, oomycetes) that form a variety of different interactions (pathogenic, symbiotic) with plant organs/tissues (leaves, roots). With the explosion in microbial/host genome sequences and the identification of genes/proteins involved in these interactions, the focus of the field is moving rapidly towards using cell and molecular biology techniques and new imaging technologies to understand the molecular dialogue between plants and their microbial pathogens/symbionts. The need for a conference on this topic, the first of its type, is evidenced by the growing prominence of cell biology in the literature. Students and scientists in this field face many challenges in the application and interpretation of cell biology data and would greatly benefit from a specialized conference on this topic. The symposium will bring together a broad representation of researchers focussing on different cell biology aspects and will allow researchers across the different disciplines to present and exchange their recent advances in this important topic of plant biology.

Symposium rationale and scope - Plant organs are subject to colonisation and manipulation by microbes, and this requires reprogramming of host cell biology to accommodate microbial structures within tissues/cells and to mediate responses for proper immunity or for symbiosis. Host cell biology changes during microbial invasion were first reported more than 100 years ago based on microscopy studies revealing that many microbes project structures (haustoria, arbuscules) into plant cells that are enveloped with a specialized plant-­derived membrane and evidence now suggests an intimate molecular exchange takes place across these membrane interfaces. However, recent identification of some of the molecular players in these interactions is only now providing appropriate tools to analyse these events. The symposium will focus on advances in understanding the molecular interactions that occur between a microbe and its host at a cellular and subcellular level, such as:

how root and leaf cells accommodate microbial structures through biogenesis of specialized plant derived membranes, microbial invasion and spreading strategies (via stomata, roots, vasculature, plasmodesmata), the dynamic localization of cell surface and cytosolic receptors recognizing microbial signals the reprogramming of host membrane trafficking (focal accumulation, secretion), the delivery of microbial molecules from fungal and oomycete species into plant cells.

With recent advances in high resolution/throughput bioimaging we are gaining new insights into the cell biology mechanisms and pathways of plant cell interactions with diverse microbes. Therefore the symposium provides a timely and important opportunity to overview the application of these technologies to plant–microbe interactions, and to discuss recent discoveries emerging from diverse host–microbe interactions illustrating common underlying principles and differences of strategies used by the microbes to gain access to plant tissues/cells. The symposium will certainly trigger a wealth of discussions, exchange of findings and methodologies, and will promote new lines of research and ideas in this rapidly expanding field.


Via Kamoun Lab @ TSL, Nicolas Denancé
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Modulation of RNA Polymerase II Phosphorylation Downstream of Pathogen Perception Orchestrates Plant Immunity: Cell Host & Microbe

Modulation of RNA Polymerase II Phosphorylation Downstream of Pathogen Perception Orchestrates Plant Immunity: Cell Host & Microbe | Plant-microbe interaction | Scoop.it
Highlights


•RNA polymerase II CTD phosphatase (CPL3) mutants show enhanced immune gene activation
•MAMPs induce cyclin-dependent kinases CDKCs and RNA pol II CTD phosphorylation
•Direct CDKC phosphorylation by MAP kinase (MAPK) activates immune gene expression
•CPL3 counteracts MAPK-CDKC regulation via RNA pol II CTD dephosphorylation

 

Summary
Perception of microbe-associated molecular patterns (MAMPs) elicits host transcriptional reprogramming as part of the immune response. Although pathogen perception is well studied, the signaling networks orchestrating immune gene expression remain less clear. In a genetic screen for components involved in the early immune gene transcription reprogramming, we identified Arabidopsis RNA polymerase II C-terminal domain (CTD) phosphatase-like 3 (CPL3) as a negative regulator of immune gene expression. MAMP perception induced rapid and transient cyclin-dependent kinase C (CDKC)-mediated phosphorylation of Arabidopsis CTD. The CDKCs, which are in turn phosphorylated and activated by a canonical MAP kinase (MAPK) cascade, represent a point of signaling convergence downstream of multiple immune receptors. CPL3 directly dephosphorylated CTD to counteract MAPK-mediated CDKC regulation. Thus, modulation of the phosphorylation dynamics of eukaryotic RNA polymerase II transcription machinery by MAPKs, CTD kinases, and phosphatases constitutes an essential mechanism for rapid orchestration of host immune gene expression and defense upon pathogen attacks.

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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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Rescooped by Suayib Üstün from Plant immunity and legume symbiosis
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A fluorescent hormone biosensor reveals the dynamics of jasmonate signalling in plants : Nature Communications : Nature Publishing Group

A fluorescent hormone biosensor reveals the dynamics of jasmonate signalling in plants : Nature Communications : Nature Publishing Group | Plant-microbe interaction | Scoop.it
Activated forms of jasmonic acid (JA) are central signals coordinating plant responses to stresses, yet tools to analyse their spatial and temporal distribution are lacking. Here we describe a JA perception biosensor termed Jas9-VENUS that allows the quantification of dynamic changes in JA distribution in response to stress with high spatiotemporal sensitivity. We show that Jas9-VENUS abundance is dependent on bioactive JA isoforms, the COI1 co-receptor, a functional Jas motif and proteasome activity. We demonstrate the utility of Jas9-VENUS to analyse responses to JA in planta at a cellular scale, both quantitatively and dynamically. This included using Jas9-VENUS to determine the cotyledon-to-root JA signal velocities on wounding, revealing two distinct phases of JA activity in the root. Our results demonstrate the value of developing quantitative sensors such as Jas9-VENUS to provide high-resolution spatiotemporal data about hormone distribution in response to plant abiotic and biotic stresses.

Via Christophe Jacquet
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Rescooped by Suayib Üstün from microbial pathogenesis and plant immunity
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PLOS One: Immunomodulation by the Pseudomonas syringae HopZ Type III Effector Family in Arabidopsis

PLOS One: Immunomodulation by the Pseudomonas syringae HopZ Type III Effector Family in Arabidopsis | Plant-microbe interaction | Scoop.it

Pseudomonas syringae employs a type III secretion system to inject 20–30 different type III effector (T3SE) proteins into plant host cells. A major role of T3SEs is to suppress plant immune responses and promote bacterial infection. The YopJ/HopZ acetyltransferases are a superfamily of T3SEs found in both plant and animal pathogenic bacteria. In P. syringae, this superfamily includes the evolutionarily diverse HopZ1, HopZ2 and HopZ3 alleles. To investigate the roles of the HopZ family in immunomodulation, we generated dexamethasone-inducible T3SE transgenic lines of Arabidopsis for HopZ family members and characterized them for immune suppression phenotypes. We show that all of the HopZ family members can actively suppress various facets of Arabidopsis immunity in a catalytic residue-dependent manner. HopZ family members can differentially suppress the activation of mitogen-activated protein (MAP) kinase cascades or the production of reactive oxygen species, whereas all members can promote the growth of non-virulent P. syringae. Localization studies show that four of the HopZ family members containing predicted myristoylation sites are localized to the vicinity of the plasma membrane while HopZ3 which lacks the myristoylation site is at least partially nuclear localized, suggesting diversification of immunosuppressive mechanisms. Overall, we demonstrate that despite significant evolutionary diversification, all HopZ family members can suppress immunity in Arabidopsis.


Via Christophe Jacquet, Jim Alfano
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Rhizobium–legume symbioses: the crucial role of plant immunity: Trends in Plant Science

Rhizobium–legume symbioses: the crucial role of plant immunity: Trends in Plant Science | Plant-microbe interaction | Scoop.it
Highlights


•Nod factors that elicit legume nodule organogenesis also suppress plant immunity.
•The rhizobial type III secretion system (T3SS) can influence host range.
•Resistance gene-mediated immunity can impact upon rhizobial host range.
•Management of host defenses is also important for the maintenance of symbiosis.
•The plant growth environment can impact upon plant defense and symbiosis.
New research results have significantly revised our understanding of the rhizobium–legume infection process. For example, Nod factors (NFs), previously thought to be absolutely essential for this symbiosis, were shown to be dispensable under particular conditions. Similarly, an NF receptor, previously considered to be solely involved in symbiosis, was shown to function during plant pathogen infections. Indeed, there is a growing realization that plant innate immunity is a crucial component in the establishment and maintenance of symbiosis. We review here the factors involved in the suppression of plant immunity during rhizobium–legume symbiosis, and we attempt to place this information into context with the most recent and sometimes surprising research results.

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Loss of Arabidopsis thaliana Dynamin-Related Protein 2B Reveals Separation of Innate Immune Signaling Pathways

Loss of Arabidopsis thaliana Dynamin-Related Protein 2B Reveals Separation of Innate Immune Signaling Pathways | Plant-microbe interaction | Scoop.it
Vesicular trafficking has emerged as an important means by which eukaryotes modulate responses to microbial pathogens, likely by contributing to the correct localization and levels of host components necessary for effective immunity. However, considering the complexity of membrane trafficking in plants, relatively few vesicular trafficking components with functions in plant immunity are known. Here we demonstrate that Arabidopsis thaliana Dynamin-Related Protein 2B (DRP2B), which has been previously implicated in constitutive clathrin-mediated endocytosis (CME), functions in responses to flg22 (the active peptide derivative of bacterial flagellin) and immunity against flagellated bacteria Pseudomonas syringae pv. tomato (Pto) DC3000. Consistent with a role of DRP2B in Pattern-Triggered Immunity (PTI), drp2b null mutant plants also showed increased susceptibility to Pto DC3000 hrcC−, which lacks a functional Type 3 Secretion System, thus is unable to deliver effectors into host cells to suppress PTI. Importantly, analysis of drp2b mutant plants revealed three distinct branches of the flg22-signaling network that differed in their requirement for RESPIRATORY BURST OXIDASE HOMOLOGUE D (RBOHD), the NADPH oxidase responsible for flg22-induced apoplastic reactive oxygen species production. Furthermore, in drp2b, normal MAPK signaling and increased immune responses via the RbohD/Ca2+-branch were not sufficient for promoting robust PR1 mRNA expression nor immunity against Pto DC3000 and Pto DC3000 hrcC−. Based on live-cell imaging studies, flg22-elicited internalization of the plant flagellin-receptor, FLAGELLIN SENSING 2 (FLS2), was found to be partially dependent on DRP2B, but not the closely related protein DRP2A, thus providing genetic evidence for a component, implicated in CME, in ligand-induced endocytosis of FLS2. Reduced trafficking of FLS2 in response to flg22 may contribute in part to the non-canonical combination of immune signaling defects observed in drp2b. In conclusion, this study adds DRP2B to the relatively short list of known vesicular trafficking proteins with roles in flg22-signaling and PTI in plants.
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The Pseudomonas syringae Type III Effector HopF2 Suppresses Arabidopsis Stomatal Immunity

The Pseudomonas syringae Type III Effector HopF2 Suppresses Arabidopsis Stomatal Immunity | Plant-microbe interaction | Scoop.it

Pseudomonas syringae subverts plant immune signalling through injection of type III secreted effectors (T3SE) into host cells. The T3SE HopF2 can disable Arabidopsis immunity through Its ADP-ribosyltransferase activity. Proteomic analysis of HopF2 interacting proteins identified a protein complex containing ATPases required for regulating stomatal aperture, suggesting HopF2 may manipulate stomatal immunity. Here we report HopF2 can inhibit stomatal immunity independent of its ADP-ribosyltransferase activity. Transgenic expression of HopF2 in Arabidopsis inhibits stomatal closing in response to P. syringae and increases the virulence of surface inoculated P. syringae. Further, transgenic expression of HopF2 inhibits flg22 induced reactive oxygen species production. Intriguingly, ADP-ribosyltransferase activity is dispensable for inhibiting stomatal immunity and flg22 induced reactive oxygen species. Together, this implies HopF2 may be a bifunctional T3SE with ADP-ribosyltransferase activity required for inhibiting apoplastic immunity and an independent function required to inhibit stomatal immunity.

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Pepper Heat Shock Protein 70a Interacts with the Type III Effector AvrBsT and Triggers Plant Cell Death and Immunity

Pepper Heat Shock Protein 70a Interacts with the Type III Effector AvrBsT and Triggers Plant Cell Death and Immunity | Plant-microbe interaction | Scoop.it
Heat shock proteins (HSPs) function as molecular chaperones and are essential for the maintenance and/or restoration of protein homeostasis. The Xanthomonas type III effector AvrBsT induces hypersensitive cell death in pepper (Capsicum annuum). Here, we report the identification of the pepper CaHSP70a as an AvrBsT-interacting protein. Bimolecular fluorescence complementation and co-immunoprecipitation assays confirm the specific interaction between CaHSP70a and AvrBsT in planta. The CaHSP70a peptide-binding domain is essential for its interaction with AvrBsT. Heat stress (37°C) and Xanthomonas campestris pv. vesicatoria (Xcv) infection distinctly induce CaHSP70a in pepper leaves. Cytoplasmic CaHSP70a proteins significantly accumulate in pepper leaves to induce the hypersensitive cell death response by Xcv (avrBsT) infection. Transient CaHSP70a overexpression induces hypersensitive cell death under heat stress, which is accompanied by strong induction of defense- and cell death-related genes. CaHSP70a peptide-binding domain and ATPase-binding domain are required to trigger cell death under heat stress. Transient co-expression of CaHSP70a and avrBsT leads to cytoplasmic localization of the CaHSP70a-AvrBsT complex, and significantly enhances avrBsT-triggered cell death in Nicotiana benthamiana. CaHSP70a silencing in pepper enhances Xcv growth, but disrupts the reactive oxygen species burst and cell death response during Xcv infection. Expression of some defense marker genes is significantly reduced in CaHSP70a-silenced leaves, with lower levels of the defense hormones salicylic acid and jasmonic acid. Together, these results suggest that CaHSP70a interacts with the type III effector AvrBsT and is required for cell death and immunity in plants.
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