Effectors and Plant Immunity
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Effectors and Plant Immunity
Strategies of plant defense and microbe attacks
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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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Nature Reviews Immunology: Effector-triggered versus pattern-triggered immunity: how animals sense pathogens (2013)

Nature Reviews Immunology: Effector-triggered versus pattern-triggered immunity: how animals sense pathogens (2013) | Effectors and Plant Immunity | Scoop.it

http://www.nature.com/nri/journal/vaop/ncurrent/full/nri3398.html

 

A fundamental question regarding any immune system is how it can discriminate between pathogens and non-pathogens. Here, we discuss how this discrimination can be mediated by a surveillance system distinct from pattern-recognition receptors that recognize conserved microbial patterns. It can be based instead on the ability of the host to sense perturbations in host cells induced by bacterial toxins or 'effectors' that are encoded by pathogenic microorganisms. Such 'effector-triggered immunity' was previously demonstrated mainly in plants, but recent data confirm that animals can also use this strategy.

 

Lynda M. Stuart, Nicholas Paquette & Laurent Boyer


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Jennifer Mach's comment, February 19, 2013 8:36 AM
"...previously demonstrated mainly in plants, but recent data confirm that animals can also use this strategy." This sentence should be read by all granting agencies.
Freddy Monteiro's comment, February 19, 2013 9:47 AM
with all due respect, this was the kind of information and approach I was expecting at the 2012 IS-MPMI Congress opening lecture.
Kamoun Lab @ TSL's comment, February 20, 2013 10:44 PM
Freddy, yes you have a point. Sadly, our animal immunity colleagues seem oblivious to the plant literature. I think the authors of this review have earned themselves many invitations on the plant biology lecture circuit.
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Genome Announcements: Genome Sequence of Xanthomonas campestris pv. campestris Strain Xca5 (2013)

An annotated high-quality draft genome sequence for Xanthomonas campestris pv. campestris race 1 strain Xca5 (originally described as X. campestris pv. armoraciae), the causal agent of black rot on Brassicaceae plants, has been determined. This genome sequence is a valuable resource for comparative genomics within the campestris pathovar.

 

Stéphanie Bolot, Endrick Guy, Sébastien Carrere, Valérie Barbe, Matthieu Arlat, Laurent D. Noël

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G3: Comparative Genomics of a Plant-Pathogenic Fungus, Pyrenophora tritici-repentis, Reveals Transduplication and the Impact of Repeat Elements on Pathogenicity and Population Divergence (2013)

G3: Comparative Genomics of a Plant-Pathogenic Fungus, Pyrenophora tritici-repentis, Reveals Transduplication and the Impact of Repeat Elements on Pathogenicity and Population Divergence (2013) | Effectors and Plant Immunity | Scoop.it

Pyrenophora tritici-repentis is a necrotrophic fungus causal to the disease tan spot of wheat, whose contribution to crop loss has increased significantly during the last few decades. Pathogenicity by this fungus is attributed to the production of host-selective toxins (HST), which are recognized by their host in a genotype-specific manner. To better understand the mechanisms that have led to the increase in disease incidence related to this pathogen, we sequenced the genomes of three P. tritici-repentis isolates. A pathogenic isolate that produces two known HSTs was used to assemble a reference nuclear genome of approximately 40 Mb composed of 11 chromosomes that encode 12,141 predicted genes. Comparison of the reference genome with those of a pathogenic isolate that produces a third HST, and a nonpathogenic isolate, showed the nonpathogen genome to be more diverged than those of the two pathogens. Examination of gene-coding regions has provided candidate pathogen-specific proteins and revealed gene families that may play a role in a necrotrophic lifestyle. Analysis of transposable elements suggests that their presence in the genome of pathogenic isolates contributes to the creation of novel genes, effector diversification, possible horizontal gene transfer events, identified copy number variation, and the first example of transduplication by DNA transposable elements in fungi. Overall, comparative analysis of these genomes provides evidence that pathogenicity in this species arose through an influx of transposable elements, which created a genetically flexible landscape that can easily respond to environmental changes.

 

Viola A. Manning, Iovanna Pandelova, Braham Dhillon, Larry J. Wilhelm, Stephen B. Goodwin, Aaron M. Berlin, Melania Figueroa, Michael Freitag, James K. Hane, Bernard Henrissa, Wade H. Holman, Chinnappa D. Kodira, Joel Martin, Richard P. Oliver, Barbara Robbertse, Wendy Schackwitz, David C. Schwartz, Joseph W. Spatafora, B. Gillian Turgeon, Chandri Yandava, Sarah Young, Shiguo Zhou, Qiandong Zeng, Igor V. Grigoriev, Li-Jun Ma, and Lynda M. Ciuffetti


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PNAS: NADPH oxidases regulate septin-mediated cytoskeletal remodeling during plant infection by the rice blast fungus (2013)

PNAS: NADPH oxidases regulate septin-mediated cytoskeletal remodeling during plant infection by the rice blast fungus (2013) | Effectors and Plant Immunity | Scoop.it

The rice blast fungus Magnaporthe oryzae infects plants with a specialized cell called an appressorium, which uses turgor to drive a rigid penetration peg through the rice leaf cuticle. Here, we show that NADPH oxidases (Nox) are necessary for septin-mediated reorientation of the F-actin cytoskeleton to facilitate cuticle rupture and plant cell invasion. We report that the Nox2–NoxR complex spatially organizes a heteroligomeric septin ring at the appressorium pore, required for assembly of a toroidal F-actin network at the point of penetration peg emergence. Maintenance of the cortical F-actin network during plant infection independently requires Nox1, a second NADPH oxidase, which is necessary for penetration hypha elongation. Organization of F-actin in appressoria is disrupted by application of antioxidants, whereas latrunculin-mediated depolymerization of appressorial F-actin is competitively inhibited by reactive oxygen species, providing evidence that regulated synthesis of reactive oxygen species by fungal NADPH oxidases directly controls septin and F-actin dynamics.

 

Lauren S. Ryder, Yasin F. Dagdas, Thomas A. Mentlak, Michael J. Kershaw, Christopher R. Thornton, Martin Schuster, Jisheng Chen, Zonghua Wang, and Nicholas J. Talbot


Via Elsa Ballini, Kamoun Lab @ TSL
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Trends Plant Sci.: CDPKs in immune and stress signaling (2013)

Trends Plant Sci.: CDPKs in immune and stress signaling (2013) | Effectors and Plant Immunity | Scoop.it

Ca2+ has long been recognized as a conserved second messenger and principal mediator in plant immune and stress responses. How Ca2+ signals are sensed and relayed into diverse primary and global signaling events is still largely unknown. Comprehensive analyses of the plant-specific multigene family of Ca2+-dependent protein kinases (CDPKs) are unraveling the molecular, cellular and genetic mechanisms of Ca2+ signaling. CDPKs, which exhibit overlapping and distinct expression patterns, sub-cellular localizations, substrate specificities and Ca2+ sensitivities, play versatile roles in the activation and repression of enzymes, channels and transcription factors. Here, we review the recent advances on the multifaceted functions of CDPKs in the complex immune and stress signaling networks, including oxidative burst, stomatal movements, hormonal signaling and gene regulation.

 

Marie Boudsocq, Jen Sheen

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Plant Cell: The Ubiquitin Ligase PUB22 Targets a Subunit of the Exocyst Complex Required for PAMP-Triggered Responses in Arabidopsis (2012)

Plant Cell: The Ubiquitin Ligase PUB22 Targets a Subunit of the Exocyst Complex Required for PAMP-Triggered Responses in Arabidopsis (2012) | Effectors and Plant Immunity | Scoop.it

Plant pathogens are perceived by pattern recognition receptors, which are activated upon binding to pathogen-associated molecular patterns (PAMPs). Ubiquitination and vesicle trafficking have been linked to the regulation of immune signaling. However, little information exists about components of vesicle trafficking involved in immune signaling and the mechanisms that regulate them. In this study, we identified Arabidopsis thaliana Exo70B2, a subunit of the exocyst complex that mediates vesicle tethering during exocytosis, as a target of the plant U-box–type ubiquitin ligase 22 (PUB22), which acts in concert with PUB23 and PUB24 as a negative regulator of PAMP-triggered responses. We show that Exo70B2 is required for both immediate and later responses triggered by all tested PAMPs, suggestive of a role in signaling. Exo70B2 is also necessary for the immune response against different pathogens. Our data demonstrate that PUB22 mediates the ubiquitination and degradation of Exo70B2 via the 26S Proteasome. Furthermore, degradation is regulated by the autocatalytic turnover of PUB22, which is stabilized upon PAMP perception. We therefore propose a mechanism by which PUB22-mediated degradation of Exo70B2 contributes to the attenuation of PAMP-induced signaling.

 

Martin Stegmann, Ryan G. Anderson, Kazuya Ichimura, Tamara Pecenkova, Patrick Reuter, Viktor Zársky, John M. McDowell, Ken Shirasu, and Marco Trujillo

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Plant J.: The Magnaporthe oryzae effector AVR1-C039 is translocated into rice cells independently of a fungal-derived machinery (2012)

Plant J.: The Magnaporthe oryzae effector AVR1-C039 is translocated into rice cells independently of a fungal-derived machinery  (2012) | Effectors and Plant Immunity | Scoop.it

Effector proteins are key elements in plant fungal interactions. The rice blast fungus Magnaporthe oryzae secretes numerous effectors suspected to be translocated inside plant cells. However, their cellular targets and the mechanisms of translocation are still unknown. Here, we have identified the open reading frame (ORF3) corresponding to the M. oryzae avirulence gene AVR1-C039 interacting with the rice resistance gene Pi-CO39 and encoding a small secreted protein without homologies to other proteins. We demonstrate that AVR1-C039 is specifically expressed and secreted at the plant fungal interface during the biotrophic phase of infection. Live cell imaging with M. oryzae transformants expressing a translational fusion between AVR1-C039 and the monomeric red fluorescent protein (mRFP), indicates that AVR1-C039 is translocated into the cytoplasm of infected rice cells. Transient expression of an AVR1-C039 isoform without signal peptide in rice protoplasts triggers a Pi-C039 specific HR suggesting that the recognition of AVR1-C039 by the Pi-C039 gene product occurs in the cytoplasm of rice cells. The native AVR1-C039 enters into the secretory pathway of rice protoplasts as demonstrated by the ER localization of AVR1-CO39:mRFP:HDEL translational fusions and is correctly processed as shown by Western blotting. However, this secreted AVR1-C039 isoform triggers Pi-CO39 specific HR and accumulates inside rice protoplasts as shown by western blotting and localisation of AVR1-C039:mRFP translational fusions. This indicates that AVR1-C039 is secreted by rice protoplasts and re-enters into the cytoplasm by unknown mechanisms suggesting that translocation of AVR1-C039 into rice cells occurs independently of fungal factors.

 

Cécile Ribot, Stella Césari, Imène Abidi, Véronique Chalvon, Caroline Bournaud, Julie Vallet, Marc-Henri Lebrun, Jean-Benoit Morel and Thomas Kroj

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J. Exp. Bot.: Signalling of Arabidopsis thaliana response to Pieris brassicae eggs shares similarities with PAMP-triggered immunity (2012)

J. Exp. Bot.: Signalling of Arabidopsis thaliana response to Pieris brassicae eggs shares similarities with PAMP-triggered immunity (2012) | Effectors and Plant Immunity | Scoop.it

Insect egg deposition activates plant defence, but very little is known about signalling events that control this response. In Arabidopsis thaliana, oviposition by Pieris brassicae triggers salicylic acid (SA) accumulation and induces the expression of defence genes. This is similar to the recognition of pathogen-associated molecular patterns (PAMPs), which are involved in PAMP-triggered immunity (PTI). Here, the involvement of known signalling components of PTI in response to oviposition was studied. Treatment with P. brassicae egg extract caused a rapid induction of early PAMP-responsive genes. In addition, expression of the defence gene PR-1 required EDS1, SID2, and, partially, NPR1, thus implicating the SA pathway downstream of egg recognition. PR-1 expression was triggered by a non-polar fraction of egg extract and by an oxidative burst modulated through the antagonistic action of EDS1 and NUDT7, but which did not depend on the NADPH oxidases RBOHD and RBOHF. Searching for receptors of egg-derived elicitors, a receptor-like kinase mutant, lecRK-I.8, was identified which shows a much reduced induction of PR-1 in response to egg extract treatment. These results demonstrate the importance of the SA pathway in response to egg-derived elicitor(s) and unravel intriguing similarities between the detection of insect eggs and PTI in Arabidopsis.

 

Caroline Gouhier-Darimont, André Schmiesing, Christelle Bonnet, Steve Lassueur, and Philippe Reymond

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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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mBio: Characterization of a Diffusible Signaling Factor from Xylella fastidiosa (2013)

mBio: Characterization of a Diffusible Signaling Factor from Xylella fastidiosa (2013) | Effectors and Plant Immunity | Scoop.it

Cell-cell signaling in Xylella fastidiosa has been implicated in the coordination of traits enabling colonization in plant hosts as well as insect vectors. This cell density-dependent signaling has been attributed to a diffusible signaling factor (DSF) produced by the DSF synthase RpfF. DSF produced by related bacterial species are unsaturated fatty acids, but that of X. fastidiosa was thought to be different from those of other taxa. We describe here the isolation and characterization of an X. fastidiosa DSF (XfDSF) as 2(Z)-tetradecenoic acid. This compound was isolated both from recombinant Erwinia herbicola expressing X. fastidiosa rpfF and from an X. fastidiosa rpfC deletion mutant that overproduces DSF. Since an rpfF mutant is impaired in biofilm formation and underexpresses the hemagglutinin-like protein-encoding genes hxfA and hxfB, we demonstrate that these traits can be restored by ca. 0.5 µM XfDSF but not by myristic acid, the fully saturated tetradecenoic acid. A phoA-based X. fastidiosa biosensor that assesses DSF-dependent expression of hxfA or hxfB revealed a high level of molecular specificity of DSF signaling.

 

IMPORTANCE X. fastidiosa causes diseases in many important plants, including grape, where it incites Pierce’s disease. Virulence of X. fastidiosa for grape is coordinated by cell-cell signaling molecules, designated DSF (Diffusible Signaling Factor). Mutants blocked in DSF production are hypervirulent for grape, suggesting that virulence is suppressed upon DSF accumulation and that disease could be controlled by artificial elevation of the DSF level in plants. In this work, we describe the isolation of the DSF produced by X. fastidiosa and the verification of its biological activity as an antivirulence factor. We also have developed X. fastidiosa DSF biosensors to evaluate the specificity of cell-cell signaling to be investigated.

 

Ellen D. Beaulieu, Michael Ionescu, Subhadeep Chatterjee, Kenji Yokota, Dirk Trauner, and Steven Lindow

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New Phytologist: The dispensable chromosome of Leptosphaeria maculans shelters an effector gene conferring avirulence towards Brassica rapa (2013)

New Phytologist: The dispensable chromosome of Leptosphaeria maculans shelters an effector gene conferring avirulence towards Brassica rapa (2013) | Effectors and Plant Immunity | Scoop.it

Phytopathogenic fungi frequently contain dispensable chromosomes, some of which contribute to host range or pathogenicity. In Leptosphaeria maculans, the stem canker agent of oilseed rape (Brassica napus), the minichromosome was previously suggested to be dispensable, without evidence for any role in pathogenicity.

Using genetic and genomic approaches, we investigated the inheritance and molecular determinant of an L. maculans–Brassica rapa incompatible interaction.

Single gene control of the resistance was found, while all markers located on the L. maculans minichromosome, absent in the virulent parental isolate, co-segregated with the avirulent phenotype. Only one candidate avirulence gene was identified on the minichromosome, validated by complementation experiments and termed AvrLm11. The minichromosome was frequently lost following meiosis, but the frequency of isolates lacking it remained stable in field populations sampled at a 10-yr time interval, despite a yearly sexual stage in the L. maculans life cycle.

This work led to the cloning of a new ‘lost in the middle of nowhere’ avirulence gene of L. maculans, interacting with a B. rapa resistance gene termed Rlm11 and introgressed into B. napus. It demonstrated the dispensability of the L. maculans minichromosome and suggested that its loss generates a fitness deficit.

 

Marie-Hélène Balesdent, Isabelle Fudal, Bénédicte Ollivier, Pascal Bally, Jonathan Grandaubert, Frédérique Eber, Anne-Marie Chèvre, Martine Leflon, Thierry Rouxel


Via Kamoun Lab @ TSL
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Stop Brown Marmorated Stink Bug (website)

Stop Brown Marmorated Stink Bug  (website) | Effectors and Plant Immunity | Scoop.it

Via Anne-Sophie Roy
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Anne-Sophie Roy's curator insight, February 8, 2013 4:16 AM

An interesting website dedicated to the Brown marmorated stink bug (Halyomorpha halys) an invasive species in the USA.

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PLOS Pathogens: Bifurcation of Arabidopsis NLR Immune Signaling via Ca2+-Dependent Protein Kinases (2013)

PLOS Pathogens: Bifurcation of Arabidopsis NLR Immune Signaling via Ca2+-Dependent Protein Kinases (2013) | Effectors and Plant Immunity | Scoop.it

Nucleotide-binding domain leucine-rich repeat (NLR) protein complexes sense infections and trigger robust immune responses in plants and humans. Activation of plant NLR resistance (R) proteins by pathogen effectors launches convergent immune responses, including programmed cell death (PCD), reactive oxygen species (ROS) production and transcriptional reprogramming with elusive mechanisms. Functional genomic and biochemical genetic screens identified six closely related Arabidopsis Ca2+-dependent protein kinases (CPKs) in mediating bifurcate immune responses activated by NLR proteins, RPS2 and RPM1. The dynamics of differential CPK1/2 activation by pathogen effectors controls the onset of cell death. Sustained CPK4/5/6/11 activation directly phosphorylates a specific subgroup of WRKY transcription factors, WRKY8/28/48, to synergistically regulate transcriptional reprogramming crucial for NLR-dependent restriction of pathogen growth, whereas CPK1/2/4/11 phosphorylate plasma membrane-resident NADPH oxidases for ROS production. Our studies delineate bifurcation of complex signaling mechanisms downstream of NLR immune sensors mediated by the myriad action of CPKs with distinct substrate specificity and subcellular dynamics.

 

Xiquan Gao, Xin Chen, Wenwei Lin, Sixue Chen, Dongping Lu, Yajie Niu, Lei Li, Cheng Cheng, Matthew McCormack, Jen Sheen, Libo Shan, Ping He


Via Suayib Üstün
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Mol. Plant: Characterization and DNA-Binding Specificities of Ralstonia TAL-like Effectors (2013)

Mol. Plant: Characterization and DNA-Binding Specificities of Ralstonia TAL-like Effectors (2013) | Effectors and Plant Immunity | Scoop.it

Ralstonia solanacearum TALE-like proteins (RTLs) exhibit similar structural features to TALEs, including a central DNA-binding domain composed of 35 amino acid-long repeats. Here, we characterize the RTLs and show that they localize in the plant cell nucleus, mediate DNA binding, and function as transcriptional activators. RTLs have a unique DNA-binding architecture and are enriched in repeat variable di-residues (RVDs), which determine repeat DNA-binding specificities. We determined the DNA-binding specificities for the RVD sequences ND, HN, NP, and NT. The RVD ND mediates highly specific interactions with C nucleotides, HN interacts specifically with A and G nucleotides, and NP specifically binds to C, A, and G nucleotides. Moreover, we developed a highly efficient repeat assembly approach for engineering RTL effectors. Taken together, our data demonstrate that RTLs are unique DNA-targeting modules that are excellent alternatives to be tailored to bind to user-selected DNA sequences for targeted genomic and epigenomic modifications. These findings will facilitate research concerning RTL molecular biology and RTL roles in the pathogenicity of Ralstonia spp.

 

Lixin Li, Ahmed Atef, Agnieszka Piatek, Zahir Ali, Marek Piatek, Mustapha Aouida, Altan Sharakou, Ali Mahjoub, Guangchao Wang, Suhail Khan, Nina V. Fedoroff, Jian-Kang Zhu and Magdy Mahfouz


Via dromius
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dromius's comment, March 24, 2013 9:01 AM
THIS MANUSCRIPT HAS BEEN RETRACTED BY THE AUTHORS!
Nicolas Denancé's comment, March 24, 2013 10:30 AM
Thanks Dromius for the info. It is always bad news when scientists retract their published work. Is it because they absolutely wanted to be the first to publish data on Ralstonia solanacearum TAL effectors so that they did not check/analyzed their results enough? Sometimes I feel sad because of this publication race. Is it really good for Science?
dromius's comment, March 24, 2013 11:36 AM
There are many reasons/motivation for rushing into publication. It will be interesting to see what follows. The webpage of the journal is not clear about that. It can be an amended version or a retraction note or a new paper...I appreciate that they retracted it rather quickly, as this prevents it from being archived in the heads of people and in reviews.
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BMC Genomics: How deep is deep enough for RNA-Seq profiling of bacterial transcriptomes? (2012)

BMC Genomics: How deep is deep enough for RNA-Seq profiling of bacterial transcriptomes? (2012) | Effectors and Plant Immunity | Scoop.it

High-throughput sequencing of cDNA libraries (RNA-Seq) has proven to be a highly effective approach for studying bacterial transcriptomes. A central challenge in designing RNA-Seq-based experiments is estimating a priori the number of reads per sample needed to detect and quantify thousands of individual transcripts with a large dynamic range of abundance. We have conducted a systematic examination of how changes in the number of RNA-Seq reads per sample influences both profiling of a single bacterial transcriptome and the comparison of gene expression among samples. Our findings suggest that the number of reads typically produced in a single lane of the Illumina HiSeq sequencer far exceeds the number needed to saturate the annotated transcriptomes of diverse bacteria growing in monoculture. Moreover, as sequencing depth increases, so too does the detection of cDNAs that likely correspond to spurious transcripts or genomic DNA contamination. Finally, even when dozens of barcoded individual cDNA libraries are sequenced in a single lane, the vast majority of transcripts in each sample can be detected and numerous genes differentially expressed between samples can be identified. Our analysis provides a guide for the many researchers seeking to determine the appropriate sequencing depth for RNA-Seq-based studies of diverse bacterial species.

 

Haas BJ, Chin M, Nusbaum C, Birren BW, Livny J

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Plant Cell: Natural Variation in Small Molecule–Induced TIR-NB-LRR Signaling Induces Root Growth Arrest via EDS1- and PAD4-Complexed R Protein VICTR in Arabidopsis (2012)

Plant Cell: Natural Variation in Small Molecule–Induced TIR-NB-LRR Signaling Induces Root Growth Arrest via EDS1- and PAD4-Complexed R Protein VICTR in Arabidopsis (2012) | Effectors and Plant Immunity | Scoop.it

In a chemical genetics screen we identified the small-molecule [5-(3,4-dichlorophenyl)furan-2-yl]-piperidine-1-ylmethanethione (DFPM) that triggers rapid inhibition of early abscisic acid signal transduction via PHYTOALEXIN DEFICIENT4 (PAD4)- and ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1)-dependent immune signaling mechanisms. However, mechanisms upstream of EDS1 and PAD4 in DFPM-mediated signaling remain unknown. Here, we report that DFPM generates an Arabidopsis thaliana accession-specific root growth arrest in Columbia-0 (Col-0) plants. The genetic locus responsible for this natural variant, VICTR (VARIATION IN COMPOUND TRIGGERED ROOT growth response), encodes a TIR-NB-LRR (for Toll-Interleukin1 Receptor–nucleotide binding–Leucine-rich repeat) protein. Analyses of T-DNA insertion victr alleles showed that VICTR is necessary for DFPM-induced root growth arrest and inhibition of abscisic acid–induced stomatal closing. Transgenic expression of the Col-0 VICTR allele in DFPM-insensitive Arabidopsis accessions recapitulated the DFPM-induced root growth arrest. EDS1 and PAD4, both central regulators of basal resistance and effector-triggered immunity, as well as HSP90 chaperones and their cochaperones RAR1 and SGT1B, are required for the DFPM-induced root growth arrest. Salicylic acid and jasmonic acid signaling pathway components are dispensable. We further demonstrate that VICTR associates with EDS1 and PAD4 in a nuclear protein complex. These findings show a previously unexplored association between a TIR-NB-LRR protein and PAD4 and identify functions of plant immune signaling components in the regulation of root meristematic zone-targeted growth arrest.

 

Tae-Houn Kim, Hans-Henning Kunz, Saikat Bhattacharjee, Felix Hauser, Jiyoung Park, Cawas Engineer, Amy Liu, Tracy Ha, Jane E. Parker, Walter Gassmann, and Julian I. Schroeder

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J. Exp. Bot.: Multiple phytohormone signalling pathways modulate susceptibility of tomato plants to Alternaria alternata f. sp. lycopersici (2012)

J. Exp. Bot.: Multiple phytohormone signalling pathways modulate susceptibility of tomato plants to Alternaria alternata f. sp. lycopersici (2012) | Effectors and Plant Immunity | Scoop.it

Three phytohormone molecules – ethylene (ET), jasmonic acid (JA) and salicylic acid (SA) – play key roles in mediating disease response to necrotrophic fungal pathogens. This study investigated the roles of the ET, JA, and SA pathways as well as their crosstalk during the interaction between tomato (Solanum lycopersicum) plants and a necrotrophic fungal pathogen Alternaria alternata f. sp. lycopersici (AAL). Both the ET and JASMONIC ACID INSENSITIVE1 (JAI1) receptor-dependent JA signalling pathways are necessary for susceptibility, while SA response promotes resistance to AAL infection. In addition, the role of JA in susceptibility to AAL is partly dependent on ET biosynthesis and perception, while the SA pathway enhances resistance to AAL and antagonizes the ET response. Based on these results, it is proposed that ET, JA, and SA each on their own can influence the susceptibility of tomato to AAL. Furthermore, the functions of JA and SA in susceptibility to the pathogen are correlated with the enhanced or decreased action of ET, respectively. This study has revealed the functional relationship among the three key hormone pathways in tomato defence against AAL.

 

Chengguo Jia, Liping Zhang, Lihong Liu, Jiansheng Wang, Chuanyou Li, and Qiaomei Wang

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