Effectors and Plant Immunity
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Effectors and Plant Immunity
Strategies of plant defense and microbe attacks
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Mol. Plant Pathol.: Ralstonia solanacearum, a widespread bacterial plant pathogen in the post-genomic era (2013)

Mol. Plant Pathol.: Ralstonia solanacearum, a widespread bacterial plant pathogen in the post-genomic era (2013) | Effectors and Plant Immunity | Scoop.it

Summary

Ralstonia solanacearum is a soil-borne bacterium causing the widespread disease known as bacterial wilt. Ralstonia solanacearum is also the causal agent of Moko disease of banana and brown rot of potato. Since the last R. solanacearum pathogen profile was published 10 years ago, studies concerning this plant pathogen have taken a genomic and post-genomic direction. This was pioneered by the first sequenced and annotated genome for a major plant bacterial pathogen and followed by many more genomes in subsequent years. All molecular features studied now have a genomic flavour. In the future, this will help in connecting the classical field of pathology and diversity studies with the gene content of specific strains. In this review, we summarize the recent research on this bacterial pathogen, including strain classification, host range, pathogenicity determinants, regulation of virulence genes, type III effector repertoire, effector-triggered immunity, plant signalling in response to R. solanacearum, as well as a review of different new pathosystems.

Taxonomy

Bacteria; Proteobacteria; β subdivision; Ralstonia group; genus Ralstonia.

Disease symptoms

Ralstonia solanacearum is the agent of bacterial wilt of plants, characterized by a sudden wilt of the whole plant. Typically, stem cross-sections will ooze a slimy bacterial exudate. In the case of Moko disease of banana and brown rot of potato, there is also visible bacterial colonization of banana fruit and potato tuber.

Disease control

As a soil-borne pathogen, infected fields can rarely be reused, even after rotation with nonhost plants. The disease is controlled by the use of resistant and tolerant plant cultivars. The prevention of spread of the disease has been achieved, in some instances, by the application of strict prophylactic sanitation practices.

Useful websites

Stock centre: International Centre for Microbial Resources—French Collection for Plant-associated Bacteria CIRM-CFBP, IRHS UMR 1345 INRA-ACO-UA, 42 rue Georges Morel, 49070 Beaucouzé Cedex, France, http://www.angers-nantes.inra.fr/cfbp/. Ralstonia Genome browser: https://iant.toulouse.inra.fr/R.solanacearum. GMI1000 insertion mutant library: https://iant.toulouse.inra.fr/R.solanacearumGMI1000/GenomicResources. MaGe Genome Browser: https://www.genoscope.cns.fr/agc/microscope/mage/viewer.php

 

Nemo Peeters, Alice Guidot, Fabienne Vailleau, and Marc Valls

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Engineering Plant Disease Resistance Based on TAL Effectors - Annual Review of Phytopathology

Engineering Plant Disease Resistance Based on TAL Effectors - Annual Review of Phytopathology | Effectors and Plant Immunity | Scoop.it

Schornack et al. (2013) [in advance version, changes will occur]

 

Transcription activator-like (TAL) effectors are encoded by plantpathogenic bacteria and induce expression of plant host genes. TAL effectors bind DNA on the basis of a unique code that specifies binding of amino acid residues in repeat units to particular DNA bases in a one-to-one correspondence. This code can be used to predict binding sites of natural TAL effectors and to design novel synthetic DNA-binding domains for targeted genome manipulation. Natural mechanisms of resistance in plants against TAL effector–containing pathogens have given insights into new strategies for disease control.


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Front. Plant Sci.: MAMP (microbe-associated molecular pattern) triggered immunity in plants (2013)

Front. Plant Sci.: MAMP (microbe-associated molecular pattern) triggered immunity in plants (2013) | Effectors and Plant Immunity | Scoop.it

Plants are sessile organisms that are under constant attack from microbes. They rely on both preformed defenses, and their innate immune system to ward of the microbial pathogens. Preformed defences include for example the cell wall and cuticle, which act as physical barriers to microbial colonization. The plant immune system is composed of surveillance systems that perceive several general microbe elicitors, which allow plants to switch from growth and development into a defense mode, rejecting most potentially harmful microbes. The elicitors are essential structures for pathogen survival and are conserved among pathogens. The conserved microbe-specific molecules, referred to as microbe- or pathogen-associated molecular patterns (MAMPs or PAMPs), are recognized by the plant innate immune systems pattern recognition receptors (PRRs). General elicitors like flagellin (Flg), elongation factor Tu (EF-Tu), peptidoglycan (PGN), lipopolysaccharides (LPS), Ax21 (Activator of XA21-mediated immunity in rice), fungal chitin, and β-glucans from oomycetes are recognized by plant surface localized PRRs. Several of the MAMPs and their corresponding PRRs have, in recent years, been identified. This review focuses on the current knowledge regarding important MAMPs from bacteria, fungi, and oomycetes, their structure, the plant PRRs that recognizes them, and how they induce MAMP-triggered immunity (MTI) in plants.

 

Mari-Anne Newman, Thomas Sundelin, Jon T. Nielsen and Gitte Erbs

 

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Database: Plant Resistance Gene Wiki (2013)

Database: Plant Resistance Gene Wiki (2013) | Effectors and Plant Immunity | Scoop.it

PRG-Wiki is an open and daily update space about plant resistance gene, in which all information about this family is stored, curated and discussed. The purpose of our work is creating a worldwide community working on plant resistance genes with a constant update on all aspects of this research field and to encourage scientists to be actors of the discussion and of the data exchange. PRG-Wiki actually stores more than 112 reference resistance gene and 104335 putative disease resistance gene. Through the wiki pages any contributor can suggest changes to the PRG database and directly update it with new data, new information and with corrections of wrong information.

 


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PLOS Pathogens: The Plant Actin Cytoskeleton Responds to Signals from Microbe-Associated Molecular Patterns (2013)

PLOS Pathogens: The Plant Actin Cytoskeleton Responds to Signals from Microbe-Associated Molecular Patterns (2013) | Effectors and Plant Immunity | Scoop.it

Plants are constantly exposed to a large and diverse array of microbes; however, most plants are immune to the majority of potential invaders and susceptible to only a small subset of pathogens. The cytoskeleton comprises a dynamic intracellular framework that responds rapidly to biotic stresses and supports numerous fundamental cellular processes including vesicle trafficking, endocytosis and the spatial distribution of organelles and protein complexes. For years, the actin cytoskeleton has been assumed to play a role in plant innate immunity against fungi and oomycetes, based largely on static images and pharmacological studies. To date, however, there is little evidence that the host-cell actin cytoskeleton participates in responses to phytopathogenic bacteria. Here, we quantified the spatiotemporal changes in host-cell cytoskeletal architecture during the immune response to pathogenic and non-pathogenic strains of Pseudomonas syringae pv. tomato DC3000. Two distinct changes to host cytoskeletal arrays were observed that correspond to distinct phases of plant-bacterial interactions i.e. the perception of microbe-associated molecular patterns (MAMPs) during pattern-triggered immunity (PTI) and perturbations by effector proteins during effector-triggered susceptibility (ETS). We demonstrate that an immediate increase in actin filament abundance is a conserved and novel component of PTI. Notably, treatment of leaves with a MAMP peptide mimic was sufficient to elicit a rapid change in actin organization in epidermal cells, and this actin response required the host-cell MAMP receptor kinase complex, including FLS2, BAK1 and BIK1. Finally, we found that actin polymerization is necessary for the increase in actin filament density and that blocking this increase with the actin-disrupting drug latrunculin B leads to enhanced susceptibility of host plants to pathogenic and non-pathogenic bacteria.

 

Jessica L. Henty-Ridilla, Masaki Shimono, Jiejie Li, Jeff H. Chang, Brad Day, Christopher J. Staiger

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Frontiers Plant Sci.: Regulate and be regulated: integration of defense and other signals by the AtMYB30 transcription factor (2013)

Frontiers Plant Sci.: Regulate and be regulated: integration of defense and other signals by the AtMYB30 transcription factor (2013) | Effectors and Plant Immunity | Scoop.it

Transcriptional regulation in host cells plays a crucial role in the establishment of plant defense and associated cell death in response to pathogen attack. Here, we review our current knowledge of the transcriptional control of plant defenses with a focus on the MYB family of transcription factors (TFs). Within this family, the Arabidopsis MYB protein AtMYB30 is a key regulator of plant defenses and one of the best characterized MYB regulators directing defense-related transcriptional responses. The crucial role played by AtMYB30 in the regulation of plant disease resistance is underlined by the finding that AtMYB30 is targeted by the Xanthomonas type III effector XopD resulting in suppression of AtMYB30-mediated plant defenses. Moreover, the function of AtMYB30 is also tightly controlled by plant cells through protein-protein interactions and post-translational modifications (PTMs). AtMYB30 studies highlight the importance of cellular dynamics for defense-associated gene regulation in plants. Finally, we discuss how AtMYB30 and other MYB TFs mediate the interplay between disease resistance and other stress responses.

 

Sylvain Raffaele and Susana Rivas

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Mary Williams's curator insight, April 14, 2013 4:09 AM

Nice review, thanks for scooping it, Nicolas!

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Hidden layer of genome unveils how plants may adapt to environments throughout the world

Hidden layer of genome unveils how plants may adapt to environments throughout the world | Effectors and Plant Immunity | Scoop.it
Hidden layer of genome unveils how plants may adapt to environments throughout the world

Via R K Upadhyay, Mary Williams
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Mary Williams's comment, March 8, 2013 3:51 AM
Here's a nice summary from Scientific American: http://www.scientificamerican.com/article.cfm?id=can-epigentics-help-crops-adapt-to-climate-change
sonia ramos's comment, March 8, 2013 4:19 AM
Thanks for the Scientific American link. I do not work on it but I found it fascinating. Evolution and adaptation throgh epigenetics. And interesting thought about epigenetics like diversity source, should be a good research line
Nanci J. Ross's curator insight, August 12, 2013 12:27 PM

This would be cool to study as a biogeography question!

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Chemistry and Biology - A Substrate-Inspired Probe Monitors Translocation, Activation, and Subcellular Targeting of Bacterial Type III Effector Protease AvrPphB

Chemistry and Biology - A Substrate-Inspired Probe Monitors Translocation, Activation, and Subcellular Targeting of Bacterial Type III Effector Protease AvrPphB | Effectors and Plant Immunity | Scoop.it

Highlights

 

Bacterial papain-like protease AvrPphB cleaves kinases in host plant cell

 

Activity-based probe for AvrPphB inspired on its unique substrate specificity

 

Secretion of ProAvrPphB through narrow type III pilus requires prodomain

 

Prodomain removal is essential to trigger cell death in resistant plants

 

Summary

 

The AvrPphB effector of Pseudomonas syringae is a papain-like protease that is injected into the host plant cell and cleaves specific kinases to disrupt immune signaling. Here, we used the unique substrate specificity of AvrPphB to generate a specific activity-based probe. This probe displays various AvrPphB isoforms in bacterial extracts, upon secretion and inside the host plant. We show that AvrPphB is secreted as a proprotease and that secretion requires the prodomain, but probably does not involve a pH-dependent unfolding mechanism. The prodomain removal is required for the ability of AvrPphB to trigger a hypersensitive cell death in resistant host plants, presumably since processing exposes a hidden acylation site required for subcellular targeting in the host cell. We detected two active isoforms of AvrPphB in planta, of which the major one localizes exclusively to membranes.


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Planty J.: Deployment of Burkholderia glumae type III secretion system as an efficient tool for translocating pathogen effectors to monocot cells (2013)

Planty J.: Deployment of Burkholderia glumae type III secretion system as an efficient tool for translocating pathogen effectors to monocot cells (2013) | Effectors and Plant Immunity | Scoop.it

Genome sequences of plant fungal pathogens have enabled the identification of effectors that cooperatively modulate the cellular environment for successful fungal growth and suppress host defense. Identification and characterization of novel effector proteins are crucial to understand pathogen virulence and host plant defense mechanisms. Previous reports indicate that the Pseudomonas syringae pv. tomato DC3000 type III secretion system (T3SS) can be used to study how non-bacterial effectors manipulate dicot plant cell function using the Effector Detector Vector (pEDV) system. Here we report a pEDV-based effector delivery system in which the T3SS of Burkholderia glumae, an emerging rice pathogen, is used to translocate the AVR-Pik and AVR-Pii effectors of fungal pathogen Magnaporthe oryzae to rice cytoplasm. The translocated AVR-Pik and AVR-Pii showed avirulence activity when tested in rice cultivars containing the cognate R genes. AVR-Pik reduced and delayed the hypersensitive response triggered by B. glumae in the non-host plant Nicotiana benthamiana indicative of an immunosuppressive virulence activity. AVR proteins fused with fluorescent protein and nuclear localization signal were delivered by B. glumae T3SS and observed in the nuclei of infected cells in rice, wheat, barley and N. benthamiana. Our bacterial T3SS-enabled eukaryotic effector delivery and subcellular localization assays provide a useful method to identify and study effector functions in monocot plants.

 

Shailendra Sharma, Shiveta Sharma, Akiko Hirabuchi, Kentaro Yoshida, Koki Fujisaki, Akiko Ito, Aiko Uemura, Ryohei Terauchi, Sophien Kamoun, Kee Hoon Sohn, Jonathan D.G. Jones and Hiromasa Saitoh

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Freddy Monteiro's comment, March 10, 2013 12:50 PM
Nico, this paper comes in time to feature in the general discussion of my dissertation, in a section where I explore if a temporal effector translocation hirarchy would exist in R. solanacearum. I wanted to cite a couple papers characterizing effector translocation in planta and this one is a perfect fit. It is amazing how the principle behind the use of NLS, so common nowadays for the characterization of oomycete effectors, could be successfully applied to bacteria pathogens. I hope this method could be useful in the future to the validation (re-validation) of pathogen effector proteins. Thank you for sharing.
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Nature Commu.: Arabidopsis ubiquitin ligase MIEL1 mediates degradation of the transcription factor MYB30 weakening plant defence (2013)

Nature Commu.: Arabidopsis ubiquitin ligase MIEL1 mediates degradation of the transcription factor MYB30 weakening plant defence (2013) | Effectors and Plant Immunity | Scoop.it

One of the most efficient plant resistance reactions to pathogen attack is the hypersensitive response, a form of programmed cell death at infection sites. The Arabidopsis transcription factor MYB30 is a positive regulator of hypersensitive cell death responses. Here we show that MIEL1 (MYB30-Interacting E3 Ligase1), an Arabidopsis RING-type E3 ubiquitin ligase that interacts with and ubiquitinates MYB30, leads to MYB30 proteasomal degradation and downregulation of its transcriptional activity. In non-infected plants, MIEL1 attenuates cell death and defence through degradation of MYB30. Following bacterial inoculation, repression of MIEL1 expression removes this negative regulation allowing sufficient MYB30 accumulation in the inoculated zone to trigger the hypersensitive response and restrict pathogen growth. Our work underlines the important role played by ubiquitination to control the hypersensitive response and highlights the sophisticated fine-tuning of plant responses to pathogen attack. Overall, this work emphasizes the importance of protein modification by ubiquitination during the regulation of transcriptional responses to stress in eukaryotic cells.

 

Daniel Marino, Solène Froidure, Joanne Canonne, Sara Ben Khaled, Mehdi Khafif, Cécile Pouzet, Alain Jauneau, Dominique Roby and Susana Rivas

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New Phytologist: NFP, a LysM protein controlling Nod factor perception, also intervenes in Medicago truncatula resistance to pathogens (2013)

New Phytologist: NFP, a LysM protein controlling Nod factor perception, also intervenes in Medicago truncatula resistance to pathogens (2013) | Effectors and Plant Immunity | Scoop.it

Plant LysM proteins control the perception of microbial-derived N-acetylglucosamine compounds for the establishment of symbiosis or activation of plant immunity. This raises questions about how plants, and notably legumes, can differentiate friends and foes using similar molecular actors and whether any receptors can intervene in both symbiosis and resistance.


To study this question, nfp and lyk3 LysM-receptor like kinase mutants of Medicago truncatula that are affected in the early steps of nodulation, were analysed following inoculation with Aphanomyces euteiches, a root oomycete. The role of NFP in this interaction was further analysed by overexpression of NFP and by transcriptome analyses.


nfp, but not lyk3, mutants were significantly more susceptible than wildtype plants to A. euteiches, whereas NFP overexpression increased resistance. Transcriptome analyses on A. euteiches inoculation showed that mutation in the NFP gene led to significant changes in the expression of c. 500 genes, notably involved in cell dynamic processes previously associated with resistance to pathogen penetration. nfp mutants also showed an increased susceptibility to the fungus Colletotrichum trifolii.


These results demonstrate that NFP intervenes in M. truncatula immunity, suggesting an unsuspected role for NFP in the perception of pathogenic signals.


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Phytopathogen type III effectors as probes of biological systems - Microbial Biotechnology

Phytopathogen type III effectors as probes of biological systems - Microbial Biotechnology | Effectors and Plant Immunity | Scoop.it

Amy Huei-Yi Lee; Maggie A. Middleton; David S. Guttman; Darrell Desveaux

 

Summary:

Bacterial phytopathogens utilize a myriad of virulence factors to modulate their plant hosts in order to promote successful pathogenesis. One potent virulence strategy is to inject these virulence proteins into plant cells via the type III secretion system. Characterizing the host targets and the molecular mechanisms of type III secreted proteins, known as effectors, has illuminated our understanding of eukaryotic cell biology. As a result, these effectors can serve as molecular probes to aid in our understanding of plant cellular processes, such as immune signalling, vesicle trafficking, cytoskeleton stability and transcriptional regulation. Furthermore, given that effectors directly and specifically interact with their targets within plant cells, these virulence proteins have enormous biotechnological potential for manipulating eukaryotic systems.


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Freddy Monteiro's curator insight, February 27, 2013 3:34 AM

For quite some time effector proteins started to be regarded as potential molecular tools to investigate cellular processes. This is an expanding field and I hope effector biology may help on our understanding of plant biology and molecular evolution dynamics.

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Plant Physiol.: Elevated Early Callose Deposition Results in Complete Penetration Resistance to Powdery Mildew in Arabidopsis (2013)

Plant Physiol.: Elevated Early Callose Deposition Results in Complete Penetration Resistance to Powdery Mildew in Arabidopsis (2013) | Effectors and Plant Immunity | Scoop.it

A common response by plants to fungal attack is deposition of callose, a (1,3)-β-glucan polymer, in the form of cell wall thickenings called papillae, at site of wall penetration. While it has been generally believed that the papillae provide a structural barrier to slow fungal penetration, this idea has been challenged in recent studies of Arabidopsis (Arabidopsis thaliana), where fungal resistance was found to be independent of callose deposition. To the contrary, we show that callose can strongly support penetration resistance when deposited in elevated amounts at early time points of infection. We generated transgenic Arabidopsis lines that express POWDERY MILDEW RESISTANT4 (PMR4), which encodes a stress-induced callose synthase, under the control of the constitutive 35S promoter. In these lines, we detected callose synthase activity that was four times higher than that in wild-type plants 6 h post inoculation with the virulent powdery mildew Golovinomyces cichoracearum. The callose synthase activity was correlated with enlarged callose deposits and the focal accumulation of green fluorescent protein-tagged PMR4 at sites of attempted fungal penetration. We observed similar results from infection studies with the nonadapted powdery mildew Blumeria graminis f. sp. hordei. Haustoria formation was prevented in resistant transgenic lines during both types of powdery mildew infection, and neither the salicylic acid-dependent nor jasmonate-dependent pathways were induced. We present a schematic model that highlights the differences in callose deposition between the resistant transgenic lines and the susceptible wild-type plants during compatible and incompatible interactions between Arabidopsis and powdery mildew.

 

Dorothea Ellinger, Marcel Naumann, Christian Falter, Claudia Zwikowics, Torsten Jamrow, Chithra Manisseri, Shauna C. Somerville, and Christian A. Voigt

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Breaking the DNA-binding code of Ralstonia solanacearum TAL effectors provides new possibilities to generate plant resistance genes against bacterial wilt disease - New Phytologist

(Via T. Lahaye & T. Schreiber) De Lange et al 2013 Ralstonia solanacearum is a devastating bacterial phytopathogen with a broad host range. Ralstonia solanacearum injected effector proteins (Rips) are key to the successful invasion of host plants. We have characterized Brg11(hrpB-regulated 11), the first identified member of a class of Rips with high sequence similarity to the transcription activator-like (TAL) effectors of Xanthomonas spp., collectively termed RipTALs. Fluorescence microscopy of in planta expressed RipTALs showed nuclear localization. Domain swaps between Brg11 and Xanthomonas TAL effector (TALE) AvrBs3 (avirulence protein triggering Bs3 resistance) showed the functional interchangeability of DNA-binding and transcriptional activation domains. PCR was used to determine the sequence of brg11 homologs from strains infecting phylogenetically diverse host plants. Brg11 localizes to the nucleus and activates promoters containing a matching effector-binding element (EBE). Brg11 and homologs preferentially activate promoters containing EBEs with a 5′ terminal guanine, contrasting with the TALE preference for a 5′ thymine. Brg11 and other RipTALs probably promote disease through the transcriptional activation of host genes. Brg11 and the majority of homologs identified in this study were shown to activate similar or identical target sequences, in contrast to TALEs, which generally show highly diverse target preferences. This information provides new options for the engineering of plants resistant to R. solanacearum.


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Plant Cell: The Rice Resistance Protein Pair RGA4/RGA5 Recognizes the Magnaporthe oryzae Effectors AVR-Pia and AVR1-CO39 by Direct Binding (2013)

Plant Cell: The Rice Resistance Protein Pair RGA4/RGA5 Recognizes the Magnaporthe oryzae Effectors AVR-Pia and AVR1-CO39 by Direct Binding (2013) | Effectors and Plant Immunity | Scoop.it

Resistance (R) proteins recognize pathogen avirulence (Avr) proteins by direct or indirect binding and are multidomain proteins generally carrying a nucleotide binding (NB) and a leucine-rich repeat (LRR) domain. Two NB-LRR protein-coding genes from rice (Oryza sativa), RGA4 and RGA5, were found to be required for the recognition of the Magnaporthe oryzae effector AVR1-CO39. RGA4 and RGA5 also mediate recognition of the unrelated M. oryzae effector AVR-Pia, indicating that the corresponding R proteins possess dual recognition specificity. For RGA5, two alternative transcripts, RGA5-A and RGA5-B, were identified. Genetic analysis showed that only RGA5-A confers resistance, while RGA5-B is inactive. Yeast two-hybrid, coimmunoprecipitation, and fluorescence resonance energy transfer–fluorescence lifetime imaging experiments revealed direct binding of AVR-Pia and AVR1-CO39 to RGA5-A, providing evidence for the recognition of multiple Avr proteins by direct binding to a single R protein. Direct binding seems to be required for resistance as an inactive AVR-Pia allele did not bind RGA5-A. A small Avr interaction domain with homology to the Avr recognition domain in the rice R protein Pik-1 was identified in the C terminus of RGA5-A. This reveals a mode of Avr protein recognition through direct binding to a novel, non-LRR interaction domain.

 

Stella Cesari, Gaëtan Thilliez, Cécile Ribot, Véronique Chalvon, Corinne Michel, Alain Jauneau, Susana Rivas, Ludovic Alaux, Hiroyuki Kanzaki, Yudai Okuyama, Jean-Benoit Morel, Elisabeth Fournier, Didier Tharreau, Ryohei Terauchi, and Thomas Kroj

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Trends Plant Sci.: Tell me more: roles of NPRs in plant immunity (2013)

Trends Plant Sci.: Tell me more: roles of NPRs in plant immunity (2013) | Effectors and Plant Immunity | Scoop.it

Plants and animals maintain evolutionarily conserved innate immune systems that give rise to durable resistances. Systemic acquired resistance (SAR) confers plant-wide immunity towards a broad spectrum of pathogens. Numerous studies have revealed that NON-EXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR) is a key regulator of SAR. Here, we review the mechanisms of NPR1 action in concert with its paralogues NPR3 and NPR4 and other SAR players. We provide insights into the mechanisms of salicylic acid (SA) perception. We discuss the binding of NPR3 and NPR4 with SA that modulates NPR1 coactivator capacity, leading to diverse immune outputs. Finally, we highlight the function of NPR1 as a bona fide SA receptor and propose a possible model of SA perception in planta.

 

Karolina M. Pajerowska-Mukhtar, David K. Emerine, M. Shahid Mukhtar

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Mol. Biol. Evol.: Coevolution and Life Cycle Specialization of Plant Cell Wall Degrading Enzymes in a Hemibiotrophic Pathogen (2013)

Mol. Biol. Evol.: Coevolution and Life Cycle Specialization of Plant Cell Wall Degrading Enzymes in a Hemibiotrophic Pathogen (2013) | Effectors and Plant Immunity | Scoop.it

Zymoseptoria tritici is an important fungal pathogen on wheat that originated in the Fertile Crescent. Its closely related sister species Z. pseudotritici and Z. ardabiliae infect wild grasses in the same region. This recently emerged host–pathogen system provides a rare opportunity to investigate the evolutionary processes shaping the genome of an emerging pathogen. Here, we investigate genetic signatures in plant cell wall degrading enzymes (PCWDEs) that are likely affected by or driving coevolution in plant-pathogen systems. We hypothesize four main evolutionary scenarios and combine comparative genomics, transcriptomics, and selection analyses to assign the majority of PCWDEs in Z. tritici to one of these scenarios. We found widespread differential transcription among different members of the same gene family, challenging the idea of functional redundancy and suggesting instead that specialized enzymatic activity occurs during different stages of the pathogen life cycle. We also find that natural selection has significantly affected at least 19 of the 48 identified PCWDEs. The majority of genes showed signatures of purifying selection, typical for the scenario of conserved substrate optimization. However, six genes showed diversifying selection that could be attributed to either host adaptation or host evasion. This study provides a powerful framework to better understand the roles played by different members of multigene families and to determine which genes are the most appropriate targets for wet laboratory experimentation, for example, to elucidate enzymatic function during relevant phases of a pathogen’s life cycle.

 

Patrick C. Brunner, Stefano F.F. Torriani, Daniel Croll, Eva H. Stukenbrock, and Bruce A. McDonald
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Nucl. Acids Res.: Quantitative analysis of TALE–DNA interactions suggests polarity effects (2013)

Nucl. Acids Res.: Quantitative analysis of TALE–DNA interactions suggests polarity effects (2013) | Effectors and Plant Immunity | Scoop.it

Transcription activator-like effectors (TALEs) have revolutionized the field of genome engineering. We present here a systematic assessment of TALE DNA recognition, using quantitative electrophoretic mobility shift assays and reporter gene activation assays. Within TALE proteins, tandem 34-amino acid repeats recognize one base pair each and direct sequence-specific DNA binding through repeat variable di-residues (RVDs). We found that RVD choice can affect affinity by four orders of magnitude, with the relative RVD contribution in the order NG > HD ∼ NN ≫ NI > NK. The NN repeat preferred the base G over A, whereas the NK repeat bound G with 103-fold lower affinity. We compared AvrBs3, a naturally occurring TALE that recognizes its target using some atypical RVD-base combinations, with a designed TALE that precisely matches ‘standard’ RVDs with the target bases. This comparison revealed unexpected differences in sensitivity to substitutions of the invariant 5′-T. Another surprising observation was that base mismatches at the 5′ end of the target site had more disruptive effects on affinity than those at the 3′ end, particularly in designed TALEs. These results provide evidence that TALE–DNA recognition exhibits a hitherto un-described polarity effect, in which the N-terminal repeats contribute more to affinity than C-terminal ones.

 

Joshua F. Meckler, Mital S. Bhakta, Moon-Soo Kim, Robert Ovadia, Chris H. Habrian, Artem Zykovich, Abigail Yu, Sarah H. Lockwood, Robert Morbitzer, Janett Elsäesser, Thomas Lahaye, David J. Segal, and Enoch P. Baldwin
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Mol. Mic.: Interplay between predicted inner-rod and gatekeeper in controlling substrate specificity of the type III secretion system (2013)

Mol. Mic.: Interplay between predicted inner-rod and gatekeeper in controlling substrate specificity of the type III secretion system (2013) | Effectors and Plant Immunity | Scoop.it

The type III secretion apparatus (T3SA) is a multi-protein complex central to the virulence of many Gram-negative pathogens. Currently, the mechanisms controlling the hierarchical addressing of needle subunits, translocators and effectors to the T3SA are still poorly understood. In Shigella, MxiC is known to sequester effectors within the cytoplasm prior to receiving the activation signal from the needle. However, molecules involved in linking the needle and MxiC are unknown. Here, we demonstrate a molecular interaction between MxiC and the predicted inner-rod component MxiI suggesting that this complex plugs the T3SA entry gate. Our results suggest that MxiI–MxiC complex dissociation facilitates the switch in secretion from translocators to effectors. We identified MxiCF206S variant, unable to interact with MxiI, which exhibits a constitutive secretion phenotype although it remains responsive to induction. Moreover, we identified the mxiIQ67A mutant that only secretes translocators, a phenotype that was suppressed by coexpression of the MxiCF206S variant. We demonstrated the interaction between MxiI and MxiC homologues in Yersinia and Salmonella. Lastly, we identified an interaction between MxiC and chaperone IpgC which contributes to understanding how translocators secretion is regulated. In summary, this study suggests the existence of a widely conserved T3S mechanism that regulates effectors secretion.

 

Youness Cherradi, Lionel Schiavolin, Simon Moussa, Alaeddine Meghraoui, Ahmed Meksem, Latéfa Biskri, Mohamed Azarkan, Abdelmounaaïm Allaoui and Anne Botteaux

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Warrior race of yellow rust on the rise in Europe

Warrior race of yellow rust on the rise in Europe | Effectors and Plant Immunity | Scoop.it
The "Warrior" race of yellow rust, first identified in 2011, is now virulent on adult plants of Claire and related varieties, according to the results of the UK Cereal Pathogen Virulence Survey.

Via CIMMYT, Int.
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EMBO J.: Pseudomonas HopU1 modulates plant immune receptor levels by blocking the interaction of their mRNAs with GRP7

EMBO J.: Pseudomonas HopU1 modulates plant immune receptor levels by blocking the interaction of their mRNAs with GRP7 | Effectors and Plant Immunity | Scoop.it

Pathogens target important components of host immunity to cause disease. The Pseudomonas syringae type III-secreted effector HopU1 is a mono-ADP-ribosyltransferase required for full virulence on Arabidopsis thaliana. HopU1 targets several RNA-binding proteins including GRP7, whose role in immunity is still unclear. Here, we show that GRP7 associates with translational components, as well as with the pattern recognition receptors FLS2 and EFR. Moreover, GRP7 binds specifically FLS2 and EFR transcripts in vivo through its RNA recognition motif. HopU1 does not affect the protein–protein associations between GRP7, FLS2 and translational components. Instead, HopU1 blocks the interaction between GRP7 and FLS2 and EFR transcripts in vivo. This inhibition correlates with reduced FLS2 protein levels upon Pseudomonas infection in a HopU1-dependent manner. Our results reveal a novel virulence strategy used by a microbial effector to interfere with host immunity.

 

Valerie Nicaise, Anna Joe, Byeong-ryool Jeong, Christin Korneli, Freddy Boutrot, Isa Westedt, Dorothee Staiger, James R Alfano and Cyril Zipfel

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Nature Commun.: The evolution and pathogenic mechanisms of the rice sheath blight pathogen (2013)

Nature Commun.: The evolution and pathogenic mechanisms of the rice sheath blight pathogen  (2013) | Effectors and Plant Immunity | Scoop.it

Rhizoctonia solani is a major fungal pathogen of rice (Oryza sativa L.) that causes great yield losses in all rice-growing regions of the world. Here we report the draft genome sequence of the rice sheath blight disease pathogen, R. solani AG1 IA, assembled using next-generation Illumina Genome Analyser sequencing technologies. The genome encodes a large and diverse set of secreted proteins, enzymes of primary and secondary metabolism, carbohydrate-active enzymes, and transporters, which probably reflect an exclusive necrotrophic lifestyle. We find few repetitive elements, a closer relationship to Agaricomycotina among Basidiomycetes, and expand protein domains and families. Among the 25 candidate pathogen effectors identified according to their functionality and evolution, we validate 3 that trigger crop defence responses; hence we reveal the exclusive expression patterns of the pathogenic determinants during host infection.


Aiping Zheng, Runmao Lin, Danhua Zhang, Peigang Qin, Lizhi Xu, Peng Ai, Lei Ding, Yanran Wang, Yao Chen, Yao Liu, Zhigang Sun, Haitao Feng, Xiaoxing Liang, Rongtao Fu, Changqing Tang, Qiao Li, Jing Zhang, Zelin Xie, Qiming Deng, Shuangcheng Li, Shiquan Wang, Jun Zhu, Lingxia Wang, Huainian Liu and Ping Li

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New Phytol.: The xylan utilization system of the plant pathogen Xanthomonas campestris pv campestris controls epiphytic life and reveals common features with oligotrophic bacteria and animal gut sy...

New Phytol.: The xylan utilization system of the plant pathogen Xanthomonas campestris pv campestris controls epiphytic life and reveals common features with oligotrophic bacteria and animal gut sy... | Effectors and Plant Immunity | Scoop.it
Xylan is a major structural component of plant cell wall and the second most abundant plant polysaccharide in nature. Here, by combining genomic and functional analyses, we provide a comprehensive picture of xylan utilization by Xanthomonas campestris pv campestris (Xcc) and highlight its role in the adaptation of this epiphytic phytopathogen to the phyllosphere. The xylanolytic activity of Xcc depends on xylan-deconstruction enzymes but also on transporters, including two TonB-dependent outer membrane transporters (TBDTs) which belong to operons necessary for efficient growth in the presence of xylo-oligosaccharides and for optimal survival on plant leaves. Genes of this xylan utilization system are specifically induced by xylo-oligosaccharides and repressed by a LacI-family regulator named XylR. Part of the xylanolytic machinery of Xcc, including TBDT genes, displays a high degree of conservation with the xylose-regulon of the oligotrophic aquatic bacterium Caulobacter crescentus. Moreover, it shares common features, including the presence of TBDTs, with the xylan utilization systems of Bacteroides ovatus and Prevotella bryantii, two gut symbionts. These similarities and our results support an important role for TBDTs and xylan utilization systems for bacterial adaptation in the phyllosphere, oligotrophic environments and animal guts. Guillaume Déjean, Servane Blanvillain-Baufumé, Alice Boulanger, Armelle Darrasse, Thomas Dugé de Bernonville, Anne-Laure Girard, Sébastien Carrére, Stevie Jamet, Claudine Zischek, Martine Lautier, Magali Solé, Daniela Büttner, Marie-Agnès Jacques, Emmanuelle Lauber, Matthieu Arlat
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The second story from Matthieu Arlat and Emmanuelle Lauber group reporting the role of Xanthomonas TBDTs.

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ScienceDirect.com - Trends in Plant Science - Evolution of the plant–microbe symbiotic ‘toolkit’

ScienceDirect.com - Trends in Plant Science - Evolution of the plant–microbe symbiotic ‘toolkit’ | Effectors and Plant Immunity | Scoop.it

Beneficial associations between plants and arbuscular mycorrhizal fungi play a major role in terrestrial environments and in the sustainability of agroecosystems. Proteins, microRNAs, and small molecules have been identified in model angiosperms as required for the establishment of arbuscular mycorrhizal associations and define a symbiotic ‘toolkit’ used for other interactions such as the rhizobia–legume symbiosis. Based on recent studies, we propose an evolutionary framework for this toolkit. Some components appeared recently in angiosperms, whereas others are highly conserved even in land plants unable to form arbuscular mycorrhizal associations. The exciting finding that some components pre-date the appearance of arbuscular mycorrhizal fungi suggests the existence of unknown roles for this toolkit and even the possibility of symbiotic associations in charophyte green algae.

 

Pierre-Marc Delaux, Nathalie Séjalon-Delmas,Guillaume Bécard,Jean-Michel Ané

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Plant Cell: Metabolic Effectors Secreted by Bacterial Pathogens: Essential Facilitators of Plastid Endosymbiosis? (2013)

Plant Cell: Metabolic Effectors Secreted by Bacterial Pathogens: Essential Facilitators of Plastid Endosymbiosis? (2013) | Effectors and Plant Immunity | Scoop.it

Under the endosymbiont hypothesis, over a billion years ago a heterotrophic eukaryote entered into a symbiotic relationship with a cyanobacterium (the cyanobiont). This partnership culminated in the plastid that has spread to forms as diverse as plants and diatoms. However, why primary plastid acquisition has not been repeated multiple times remains unclear. Here, we report a possible answer to this question by showing that primary plastid endosymbiosis was likely to have been primed by the secretion in the host cytosol of effector proteins from intracellular Chlamydiales pathogens. We provide evidence suggesting that the cyanobiont might have rescued its afflicted host by feeding photosynthetic carbon into a chlamydia-controlled assimilation pathway.

 

Steven G. Ball, Agathe Subtil, Debashish Bhattacharya, Ahmed Moustafa, Andreas P.M. Weber, Lena Gehre, Christophe Colleoni, Maria-Cecilia Arias, Ugo Cenci, and David Dauvillée

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