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Effectors and Plant Immunity
Strategies of plant defense and microbe attacks
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Mol Plant Pathol: The rust transferred proteins—a new family of effector proteins exhibiting protease inhibitor function (2012)

Mol Plant Pathol: The rust transferred proteins—a new family of effector proteins exhibiting protease inhibitor function (2012) | Effectors and Plant Immunity | Scoop.it

Only few fungal effectors have been described to be delivered into the host cell during obligate biotrophic interactions. RTP1p, from the rust fungi Uromyces fabae and U. striatus, was the first fungal protein for which localization within the host cytoplasm could be demonstrated directly. We investigated the occurrence of RTP1 homologues in rust fungi and examined the structural and biochemical characteristics of the corresponding gene products. The analysis of 28 homologues showed that members of the RTP family are most likely to occur ubiquitously in rust fungi and to be specific to the order Pucciniales. Sequence analyses indicated that the structure of the RTPp effectors is bipartite, consisting of a variable N-terminus and a conserved and structured C-terminus. The characterization of Uf-RTP1p mutants showed that four conserved cysteine residues sustain structural stability. Furthermore, the C-terminal domain exhibits similarities to that of cysteine protease inhibitors, and it was shown that Uf-RTP1p and Us-RTP1p are able to inhibit proteolytic activity in Pichia pastoris culture supernatants. We conclude that the RTP1p homologues constitute a rust fungi-specific family of modular effector proteins comprising an unstructured N-terminal domain and a structured C-terminal domain, which exhibit protease inhibitory activity possibly associated with effector function during biotrophic interactions.

 

Klara Pretsch, Ariane Kemen, Eric Kemen, Matthias Geiger, Kurt Mendgen and Ralf Voegele


Via Kamoun Lab @ TSL
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PNAS (2012): Distinct regions of the Pseudomonas syringae coiled-coil effector AvrRps4 are required for activation of immunity

PNAS (2012): Distinct regions of the Pseudomonas syringae coiled-coil effector AvrRps4 are required for activation of immunity | Effectors and Plant Immunity | Scoop.it

Gram-negative phytopathogenic bacteria translocate effector proteins into plant cells to subvert host defenses. These effectors can be recognized by plant nucleotide-binding–leucine-rich repeat immune receptors, triggering defense responses that restrict pathogen growth. AvrRps4, an effector protein from Pseudomonas syringae pv. pisi, triggers RPS4-dependent immunity in resistant accessions of Arabidopsis. To better understand the molecular basis of AvrRps4-triggered immunity, we determined the crystal structure of processed AvrRps4 (AvrRps4C, residues 134–221), revealing that it forms an antiparallel α-helical coiled coil. Structure-informed mutagenesis reveals an electronegative surface patch in AvrRps4C required for recognition by RPS4; mutations in this region can also uncouple triggering of the hypersensitive response from disease resistance. This uncoupling may result from a lower level of defense activation, sufficient for avirulence but not for triggering a hypersensitive response. Natural variation in AvrRps4 reveals distinct recognition specificities that involve a surface-exposed residue. Recently, a direct interaction between AvrRps4 and Enhanced Disease Susceptibility 1 has been implicated in activation of immunity. However, we were unable to detect direct interaction between AvrRps4 and Enhanced Disease Susceptibility 1 after coexpression in Nicotiana benthamiana or in yeast cells. How intracellular plant immune receptors activate defense upon effector perception remains an unsolved problem. The structure of AvrRps4C, and identification of functionally important residues for its activation of plant immunity, advances our understanding of these processes in a well-defined model pathosystem.

 

Kee Hoon Sohn, Richard K. Hughes, Sophie J. Piquerez, Jonathan D. G. Jones, and Mark J. Banfield

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Ann. Rev. Microbio. (2012): Microbial Population and Community Dynamics on Plant Roots and Their Feedbacks on Plant Communities

Ann. Rev. Microbio. (2012): Microbial Population and Community Dynamics on Plant Roots and Their Feedbacks on Plant Communities | Effectors and Plant Immunity | Scoop.it

The composition of the soil microbial community can be altered dramatically due to association with individual plant species, and these effects on the microbial community can have important feedbacks on plant ecology. Negative plant-soil feedback plays primary roles in maintaining plant community diversity, whereas positive plant-soil feedback may cause community conversion. Host-specific differentiation of the microbial community results from the trade-offs associated with overcoming plant defense and the specific benefits associated with plant rewards. Accumulation of host-specific pathogens likely generates negative feedback on the plant, while changes in the density of microbial mutualists likely generate positive feedback. However, the competitive dynamics among microbes depends on the multidimensional costs of virulence and mutualism, the fine-scale spatial structure within plant roots, and active plant allocation and localized defense. Because of this, incorporating a full view of microbial dynamics is essential to explaining the dynamics of plant-soil feedbacks and therefore plant community ecology.

 

James D. Bever, Thomas G. Platt, and Elise R. Morton

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Plant Physiol. (2012): Rhamnolipids elicit defence responses and induce disease resistance against biotrophic, hemibiotrophic and necrotrophic pathogens that require different signalling pathways i...

Plant Physiol. (2012): Rhamnolipids elicit defence responses and induce disease resistance against biotrophic, hemibiotrophic and necrotrophic pathogens that require different signalling pathways i... | Effectors and Plant Immunity | Scoop.it

Plant resistance to phytopathogenic microorganisms mainly relies on the activation of an innate immune response usually launched after recognition by the plant cells of microbe associated molecular patterns (MAMPs). The plant hormones, salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) have emerged as key players in the signalling networks involved in plant immunity. Rhamnolipids (RLs) are glycolipids produced by bacteria and are involved in surface motility and biofilm development. Here we report that RLs trigger an immune response in Arabidopsis characterized by signalling molecules accumulation and defence gene activation. This immune response participates to resistance against the hemibiotrophic bacterium Pseudomonas syringae pv. tomato, the biotrophic oomycete Hyaloperonospora arabidopsidis and the necrotrophic fungus Botrytis cinerea. We show that RL-mediated resistance involves different signalling pathways that depend on the type of pathogen. ET is involved in RL-induced resistance to H. arabidopsidis and to P. syringae whereas JA is essential for the resistance to B. cinerea. SA participates to the restriction of all pathogens. We also show evidences that SA-dependent plant defences are potentiated by RLs following challenge by B. cinerea or P. syringae. These results highlight a central role for SA in RL-mediated resistance. In addition to the activation of plant defence responses, antimicrobial properties of RLs are thought to participate in the protection against the fungus and the oomycete. Our data highlight the intricate mechanisms involved in plant protection triggered by a new type of molecule that can be perceived by plant cells and that also act directly onto pathogens.

 

Lisa Sanchez, Barbara Courteaux, Jane Hubert, Serge Kauffman, Jean-Hugues Renault, Christophe Clement, Fabienne Baillieul, and Stéphan Dorey

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Nature Genetics (2012): Lifestyle transitions in plant pathogenic Colletotrichum fungi deciphered by genome and transcriptome analyses

Nature Genetics (2012): Lifestyle transitions in plant pathogenic Colletotrichum fungi deciphered by genome and transcriptome analyses | Effectors and Plant Immunity | Scoop.it

Colletotrichum species are fungal pathogens that devastate crop plants worldwide. Host infection involves the differentiation of specialized cell types that are associated with penetration, growth inside living host cells (biotrophy) and tissue destruction (necrotrophy). We report here genome and transcriptome analyses of Colletotrichum higginsianum infecting Arabidopsis thaliana and Colletotrichum graminicola infecting maize. Comparative genomics showed that both fungi have large sets of pathogenicity-related genes, but families of genes encoding secreted effectors, pectin-degrading enzymes, secondary metabolism enzymes, transporters and peptidases are expanded in C. higginsianum. Genome-wide expression profiling revealed that these genes are transcribed in successive waves that are linked to pathogenic transitions: effectors and secondary metabolism enzymes are induced before penetration and during biotrophy, whereas most hydrolases and transporters are upregulated later, at the switch to necrotrophy. Our findings show that preinvasion perception of plant-derived signals substantially reprograms fungal gene expression and indicate previously unknown functions for particular fungal cell types.

 

Richard J O'Connell, Michael R Thon, Stéphane Hacquard, Stefan G Amyotte, Jochen Kleemann, Maria F Torres, Ulrike Damm, Ester A Buiate, Lynn Epstein, Noam Alkan, Janine Altmüller, Lucia Alvarado-Balderrama, Christopher A Bauser, Christian Becker, Bruce W Birren, Zehua Chen, Jaeyoung Choi, Jo Anne Crouch, Jonathan P Duvick, Mark A Farman, Pamela Gan, David Heiman, Bernard Henrissat, Richard J Howard, Mehdi Kabbage, Christian Koch, Barbara Kracher, Yasuyuki Kubo, Audrey D Law, Marc-Henri Lebrun, Yong-Hwan Lee, Itay Miyara, Neil Moore, Ulla Neumann, Karl Nordström, Daniel G Panaccione, Ralph Panstruga, Michael Place, Robert H Proctor, Dov Prusky, Gabriel Rech, Richard Reinhardt, Jeffrey A Rollins, Steve Rounsley, Christopher L Schardl, David C Schwartz, Narmada Shenoy, Ken Shirasu, Usha R Sikhakolli, Kurt Stüber, Serenella A Sukno, James A Sweigard, Yoshitaka Takano, Hiroyuki Takahara, Frances Trail, H Charlotte van der Does, Lars M Voll, Isa Will, Sarah Young, Qiandong Zeng, Jingze Zhang, Shiguo Zhou, Martin B Dickman, Paul Schulze-Lefert, Emiel Ver Loren van Themaat, Li-Jun Ma and Lisa J Vaillancourt


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J. Bact. (2012): Genome Sequence of the Rice Pathogen Pseudomonas fuscovaginae CB98818

Pseudomonas fuscovaginae is a phytopathogenic bacterium causing bacterial sheath brown rot of cereal crops. Here, we present the draft genome sequence of P. fuscovaginae CB98818, originally isolated from a diseased rice plant in China. The draft genome will aid in epidemiological studies, comparative genomics, and quarantine of this broad-host-range pathogen.

 

Guanlin Xie, Zhouqi Cui, Zhongyun Tao, Hui Qiu, He Liu, Muhammad Ibrahim, Bo Zhu, Gulei Jin, Guochang Sun, Abdulwareth Almoneafy, and Bin Li

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Plant Cell (2012): Novel Plant Immune-Priming Compounds Identified via High-Throughput Chemical Screening Target Salicylic Acid Glucosyltransferases in Arabidopsis

Plant Cell (2012): Novel Plant Immune-Priming Compounds Identified via High-Throughput Chemical Screening Target Salicylic Acid Glucosyltransferases in Arabidopsis | Effectors and Plant Immunity | Scoop.it

Plant activators are compounds, such as analogs of the defense hormone salicylic acid (SA), that protect plants from pathogens by activating the plant immune system. Although some plant activators have been widely used in agriculture, the molecular mechanisms of immune induction are largely unknown. Using a newly established high-throughput screening procedure that screens for compounds that specifically potentiate pathogen-activated cell death in Arabidopsis thaliana cultured suspension cells, we identified five compounds that prime the immune response. These compounds enhanced disease resistance against pathogenic Pseudomonas bacteria in Arabidopsis plants. Pretreatments increased the accumulation of endogenous SA, but reduced its metabolite, SA-O-b-D-glucoside. Inducing compounds inhibited two SA glucosyltransferases (SAGTs) in vitro. Double knockout plants that lack both SAGTs consistently exhibited enhanced disease resistance. Our results demonstrate that manipulation of the active free SA pool via SA-inactivating enzymes can be a useful strategy for fortifying plant disease resistance and may identify useful crop protectants.

 

Yoshiteru Noutoshi, Masateru Okazaki, Tatsuya Kida, Yuta Nishina, Yoshihiko Morishita, Takumi Ogawa, Hideyuki Suzuki, Daisuke Shibata, Yusuke Jikumaru, Atsushi Hanada, Yuji Kamiya, and Ken Shirasu


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Plant J. (2012): RPN1a, a 26S proteasome subunit, is required for innate immunity in Arabidopsis

Plant J. (2012): RPN1a, a 26S proteasome subunit, is required for innate immunity in Arabidopsis | Effectors and Plant Immunity | Scoop.it

Accumulating evidence shows that proper degradation of proteins that affect defense responses in a positive or negative manner is critical in plant immunity. However, the role of plant degradation systems such as the 26S proteasome in plant immunity is not well understood. Loss-of-function mutations in EDR2 (ENHANCED DISEASE RESISTANCE 2) lead to increased resistance to the adapted biotrophic powdery mildew pathogen Golovinomyces cichoracearum. To study the molecular interactions between powdery mildew pathogen and Arabidopsis, we performed a screen for suppressors of edr2 and found that mutation in the gene that encodes RPN1a, a subunit of the 26S proteasome, suppressed edr2-associated disease resistance phenotypes. In addition, RPN1a is required for edr1- and pmr4-mediated powdery mildew resistance and mildew-induced cell death. Furthermore, we show that rpn1a displayed enhanced susceptibility to the fungal pathogen G. cichoracearum and to virulent and avirulent bacterial Pto DC3000 strains, which indicated that rpn1a has defects in basal defense and resistance (R) protein-mediated defense. RPN1a–GFP localizes to both the nucleus and cytoplasm. Accumulation of RPN1a is affected by salicylic acid (SA) and the rpn1a mutant has defects in SA accumulation upon Pto DC3000 infection. Further analysis revealed that two other subunits of the 26S proteasome, RPT2a and RPN8a are also involved in edr2-mediated disease resistance. Based on these results, we conclude that RPN1a is required for basal defense and R protein-mediated defense. Our data provide evidence that some subunits of the 26S proteasome are involved in innate immunity in Arabidopsis.

 

Chunpeng Yao, Yingying Wu, Haozhen Nie, Dingzhong Tang

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PLoS ONE: RNA-Seq of Early-Infected Poplar Leaves by the Rust Pathogen Melampsora larici-populina Uncovers PtSultr3;5, a Fungal-Induced Host Sulfate Transporter (2012)

PLoS ONE: RNA-Seq of Early-Infected Poplar Leaves by the Rust Pathogen Melampsora larici-populina Uncovers PtSultr3;5, a Fungal-Induced Host Sulfate Transporter (2012) | Effectors and Plant Immunity | Scoop.it

Biotroph pathogens establish intimate interactions with their hosts that are conditioned by the successful secretion of effectors in infected tissues and subsequent manipulation of host physiology. The identification of early-expressed pathogen effectors and early-modulated host functions is currently a major goal to understand the molecular basis of biotrophy. Here, we report the 454-pyrosequencing transcriptome analysis of early stages of poplar leaf colonization by the rust fungus Melampsora larici-populina. Among the 841,301 reads considered for analysis, 616,879 and 649 were successfully mapped to Populus trichocarpa and M. larici-populina genome sequences, respectively. From a methodological aspect, these results indicate that this single approach is not appropriate to saturate poplar transcriptome and to follow transcript accumulation of the pathogen. We identified 19 pathogen transcripts encoding early-expressed small-secreted proteins representing candidate effectors of interest for forthcoming studies. Poplar RNA-Seq data were validated by oligoarrays and quantitatively analysed, which revealed a highly stable transcriptome with a single transcript encoding a sulfate transporter (herein named PtSultr3;5, POPTR_0006s16150) showing a dramatic increase upon colonization by either virulent or avirulent M. larici-populina strains. Perspectives connecting host sulfate transport and biotrophic lifestyle are discussed.

 

Benjamin Petre, Emmanuelle Morin, Emilie Tisserant, Stéphane Hacquard, Corinne Da Silva, Julie Poulain, Christine Delaruelle, Francis Martin, Nicolas Rouhier, Annegret Kohler, Sébastien Duplessis


Via Kamoun Lab @ TSL
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BMC Microbiology (2012): Phylogenetic analysis of a gene cluster encoding an additional, rhizobial-like type III secretion system that is narrowly distributed among Pseudomonas syringae strains

BMC Microbiology (2012): Phylogenetic analysis of a gene cluster encoding an additional, rhizobial-like type III secretion system that is narrowly distributed among Pseudomonas syringae strains | Effectors and Plant Immunity | Scoop.it

The central role of Type III secretion systems (T3SS) in bacteria-plant interactions is well established, yet unexpected findings are being uncovered through bacterial genome sequencing. Some Pseudomonas syringae strains possess an uncharacterized cluster of genes encoding putative components of a second T3SS (T3SS-2) in addition to the well characterized Hrc1 T3SS which is associated with disease lesions in host plants and with the triggering of hypersensitive response in non-host plants. The aim of this study is to perform an in silico analysis of T3SS-2, and to compare it with other known T3SSs. Based on phylogenetic analysis and gene organization comparisons, the T3SS-2 cluster of the P. syringae pv. phaseolicola strain is grouped with a second T3SS found in the pNGR234b plasmid of Rhizobium sp. These additional T3SS gene clusters define a subgroup within the Rhizobium T3SS family. Although, T3SS-2 is not distributed as widely as the Hrc1 T3SS in P. syringae strains, it was found to be constitutively expressed in P. syringae pv phaseolicola through RT-PCR experiments. The relatedness of the P. syringae T3SS-2 to a second T3SS from the pNGR234b plasmid of Rhizobium sp., member of subgroup II of the rhizobial T3SS family, indicates common ancestry and/or possible horizontal transfer events between these species. Functional analysis and genome sequencing of more rhizobia and P. syringae pathovars may shed light into why these bacteria maintain a second T3SS gene cluster in their genome.


Anastasia D. Gazi, Panagiotis F. Sarris, Vasiliki E. Fadouloglou, Spyridoula N. Charova, Nikolaos Mathioudakis, Nicholas J. Panopoulos and Michael Kokkinidis

 

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Mol. Plant Pathol. (2012): Functional genomics tools to decipher the pathogenicity mechanisms of the necrotrophic fungus Plectosphaerella cucumerina in Arabidopsis thaliana

Mol. Plant Pathol. (2012): Functional genomics tools to decipher the pathogenicity mechanisms of the necrotrophic fungus Plectosphaerella cucumerina in Arabidopsis thaliana | Effectors and Plant Immunity | Scoop.it

The analysis of the interaction between Arabidopsis thaliana and adapted (PcBMM) and nonadapted (Pc2127) isolates of the necrotrophic fungus Plectosphaerella cucumerina has contributed to the identification of molecular mechanisms controlling plant resistance to necrotrophs. To characterize the pathogenicity bases of the virulence of necrotrophic fungi in Arabidopsis, we developed P. cucumerina functional genomics tools using Agrobacterium tumefaciens-mediated transformation. We generated PcBMM-GFP and Pc2127-GFP transformants constitutively expressing the green fluorescence protein (GFP), and a collection of random T-DNA insertional PcBMM transformants. Confocal microscopy analyses of the initial stages of PcBMM-GFP infection revealed that this pathogen, like other necrotrophic fungi, does not form an appressorium or penetrate into plant cells, but causes successive degradation of leaf cell layers. By comparing the colonization of Arabidopsis wild-type plants and hypersusceptible (agb1-1 and cyp79B2cyp79B3) and resistant (irx1-6) mutants by PcBMM-GFP or Pc2127-GFP, we found that the plant immune response was already mounted at 12–18 h post-inoculation, and that Arabidopsis resistance to these fungi correlated with the time course of spore germination and hyphal growth on the leaf surface. The virulence of a subset of the PcBMM T-DNA insertional transformants was determined in Arabidopsis wild-type plants and agb1-1 mutant, and several transformants were identified that showed altered virulence in these genotypes in comparison with that of untransformed PcBMM. The T-DNA flanking regions in these fungal mutants were successfully sequenced, further supporting the utility of these functional genomics tools in the molecular characterization of the pathogenicity of necrotrophic fungi.

 

Brisa Ramos, Pablo González-Melendi, Andrea Sánchez-Vallet, Clara Sánchez-Rodríguez, Gemma López, Antonio Molina

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Video: Plant Pathology: Taking you further than you ever imagined.

In the quest to create a sustainable future, some paths are more direct...more profound...and more tuned-in to discovering the roots of the serious problems that need to be solved. And with the next generation seeing world population swell from 7 to 9 billion people, how will we sustainably increase our food, fiber and fuels using less land and fewer resources? One word: plants. And healthy plants are key. But plants get sick, too. And when disease strikes, disaster can quickly follow. That's why it's more important than ever that today's brightest and best choose their course wisely...and explore new paths that get to the root of some of the most critical problems. For those with insight...for those ready to make an impact, plant pathology is a path that can take you further than you'd ever imagined, or exactly where you'd like to be.

 

Learn about Plant Pathology through this exciting educational video. This video targets undergraduates in biology and related majors with limited agricultural background, and is available for use in classroom settings, on organization websites, on display at career fairs. You can also share it with your colleagues, the opportunities are endless.

To find out more about how to spread the word visit the American Phytopathological Society's website. www.apsnet.org

 

APS also has significant outreach resources. If this video piques your interest, check out our other tools for teach and growing plant pathology. http://www.apsnet.org/members/outreach


Via Kamoun Lab @ TSL
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PLoS Pathogens (2012): Five Mechanisms of Manipulation by Bacterial Effectors: A Ubiquitous Theme

PLoS Pathogens (2012): Five Mechanisms of Manipulation by Bacterial Effectors: A Ubiquitous Theme | Effectors and Plant Immunity | Scoop.it

Ubiquitin, a highly conserved polypeptide of 76 amino acids, participates in a vast range of eukaryotic cell processes through its role as a reversible post-translational modifier. Such extensive utilization of a single protein within a host cell lends itself to be an ideal target for microbial manipulation. Host-pathogen co-evolution has endowed present-day pathogens with an ever-expanding repertoire of proteins that function to modulate this system. The majority of these proteins are effectors of type III secretion (T3S) or type IV secretion (T4S) pathways, which are major virulence determinants of many Gram-negative pathogens. This review is focused on five distinct mechanisms in which secreted bacterial effector proteins exploit the host ubiquitylation system


David M. Anderson and Dara W. Frank

 

 

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Mol. Mic. (2012): Heterologous assembly of type IV pili by a type II secretion system reveals the role of minor pilins in assembly initiation

Mol. Mic. (2012): Heterologous assembly of type IV pili by a type II secretion system reveals the role of minor pilins in assembly initiation | Effectors and Plant Immunity | Scoop.it

In Gram-negative bacteria, type IV pilus assembly (T4PS) and type II secretion (T2SS) systems polymerize inner membrane proteins called major pilins or pseudopilins respectively, into thin filaments. Four minor pilins are required in both systems for efficient fibre assembly. Escherichia coli K-12 has a set of T4PS assembly genes that are silent under standard growth conditions. We studied the heterologous assembly of the E. coli type IV pilin PpdD by the Klebsiella oxytoca T2SS called the Pul system. PpdD pilus assembly in this context depended on the expression of the K. oxytoca minor pseudopilin genes pulHIJK or of the E. coli minor pilin genes ppdAB-ygdB-ppdC. The E. coli minor pilins restored assembly of the major pseudopilin PulG in a pulHIJK mutant, but not the secretion of the T2SS substrate pullulanase. Thus, minor pilins and minor pseudopilins are functionally interchangeable in initiating major pilin assembly, further extending the fundamental similarities between the two systems. The data suggest that, in both systems, minor pilins activate the assembly machinery through a common self-assembly mechanism. When produced together, PulG and PpdD assembled into distinct homopolymers, establishing major pilins as key determinants of pilus elongation and structure.

 

David A. Cisneros, Gerard Pehau-Arnaudet, Olivera Francetic

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Ann. Rev. Microbio. (2012): Structure and Regulation of the Type VI Secretion System

Ann. Rev. Microbio. (2012): Structure and Regulation of the Type VI Secretion System | Effectors and Plant Immunity | Scoop.it

The type VI secretion system (T6SS) is a complex and widespread gram-negative bacterial export pathway with the capacity to translocate protein effectors into a diversity of target cell types. Current structural models of the T6SS indicate that the apparatus is composed of at least two complexes, a dynamic bacteriophage-like structure and a cell-envelope-spanning membrane-associated assembly. How these complexes interact to promote effector secretion and cell targeting remains a major question in the field. As a contact-dependent pathway with specific cellular targets, the T6SS is subject to tight regulation. Thus, the identification of regulatory elements that control T6S expression continues to shape our understanding of the environmental circumstances relevant to its function. This review discusses recent progress toward characterizing T6S structure and regulation.

 

Julie M. Silverman,Yannick R. Brunet, Eric Cascales,and Joseph D. Mougous

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Plant Physiol. (2012): Microbe-Associated Molecular Patterns (MAMPs)-triggered root responses mediate beneficial rhizobacterial recruitment in Arabidopsis

Plant Physiol. (2012): Microbe-Associated Molecular Patterns (MAMPs)-triggered root responses mediate beneficial rhizobacterial recruitment in Arabidopsis | Effectors and Plant Immunity | Scoop.it

Our recent study demonstrated that foliar infection by Pseudomonas syringae pv. tomato (hereafter PstDC3000) induced malic acid (MA) transporter (ALMT1) expression leading to increased beneficial rhizobacteria Bacillus subtilis FB17 (hereafter FB17) colonization in plants against PstDC3000. Having shown that a live pathogen could induce an intra-plant signal from shoot-to-root to recruit FB17 belowground, we hypothesized that pathogen derived microbe-associated molecular patterns (MAMPs) may relay a similar response specific to FB17 recruitment. Plants subjected to known MAMPs such as a flagellar peptide, flagellin (flg22), and a pathogen-derived phytotoxin, coronatine (COR) induced a shoot-to-root signal regulating ALMT1 for recruitment of FB17. The data suggests that MAMPs-induced signaling to regulate ALMT1 is salicylic acid (SA) and JAR1/JIN1/MYC2 independent. Interestingly, a cell culture filtrate of FB17 suppressed flg22-induced MAMPs-activated root defense responses, which are similar to suppression of COR-mediated MAMPs-activated root defense, revealing a diffusible bacterial component that may regulate plant immune responses. Further analysis showed that the biofilm formation in B. subtilis, negate suppression of MAMPs-activated defense responses in roots. Moreover, B. subtilis suppression of MAMPs-activated root defense does require JAR1/JIN1/MYC2. The ability of FB17 to block the MAMPs-elicited signaling pathways related to antibiosis reflects a strategy adapted by FB17 for efficient root colonization. These experiments demonstrate a remarkable strategy adapted by beneficial rhizobacteria to suppress a host defense response which may facilitate rhizobacterial colonization and host-mutualistic association.

 

Venkatchalam Lakshmannan, Sherry Kitto, Jeff Caplan, Yi-Huang Hsueh, Dan Kearns, Yu-Sung Wu, and Harsh Bais

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Current Opinion in Plant Biology (2012): Plants and pathogens: putting infection strategies and defence mechanisms on the map

Current Opinion in Plant Biology (2012): Plants and pathogens: putting infection strategies and defence mechanisms on the map | Effectors and Plant Immunity | Scoop.it

All plant organs are vulnerable to colonisation and molecular manipulation by microbes. When this interaction allows proliferation of the microbe at the expense of the host, the microbe can be described as a pathogen. In our attempts to understand the full nature of the interactions that occur between a potential pathogen and its host, various aspects of the molecular mechanisms of infection and defence have begun to be characterised. There is significant variation in these mechanisms. While previous research has examined plant–pathogen interactions with whole plant/organ resolution, the specificity of infection strategies and changes in both gene expression and protein localisation of immune receptors upon infection suggest there is much to be gained from examination of plant-microbe interactions at the cellular level.

 

Christine Faulkner and Silke Robatzek

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Cell (2012): Retrograde Signaling by the Plastidial Metabolite MEcPP Regulates Expression of Nuclear Stress-Response Genes

Cell (2012): Retrograde Signaling by the Plastidial Metabolite MEcPP Regulates Expression of Nuclear Stress-Response Genes | Effectors and Plant Immunity | Scoop.it

Plastid-derived signals are known to coordinate expression of nuclear genes encoding plastid-localized proteins in a process termed retrograde signaling. To date, the identity of retrograde-signaling molecules has remained elusive. Here, we show that methylerythritol cyclodiphosphate (MEcPP), a precursor of isoprenoids produced by the plastidial methylerythritol phosphate (MEP) pathway, elicits the expression of selected stress-responsive nuclear-encoded plastidial proteins. Genetic and pharmacological manipulations of the individual MEP pathway metabolite levels demonstrate the high specificity of MEcPP as an inducer of these targeted stress-responsive genes. We further demonstrate that abiotic stresses elevate MEcPP levels, eliciting the expression of the aforementioned genes. We propose that the MEP pathway, in addition to producing isoprenoids, functions as a stress sensor and a coordinator of expression of targeted stress-responsive nuclear genes via modulation of the levels of MEcPP, a specific and critical retrograde-signaling metabolite.

 

Yanmei Xiao, Tatyana Savchenko, Edward E.K. Baidoo, Wassim E. Chehab, Daniel M. Hayden, Vladimir Tolstikov, Jason A. Corwin, Daniel J. Kliebenstein, Jay D. Keasling, Katayoon Dehesh


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Glomerella Leaf Spot – a new disease affecting Golden Delicious apples in NY?

Glomerella Leaf Spot – a new disease affecting Golden Delicious apples in NY? | Effectors and Plant Immunity | Scoop.it

Golden Delicious apple trees in Hudson Valley Lab research orchard are yellowing and defoliating. Upon closer inspection, it is suspected that it could be a fungal disease (Glomerella leaf spot ).

 

http://blogs.cornell.edu/fruit/2012/08/31/glomerella-leaf-spot-a-new-disease-affecting-golden-delicious-apples-in-ny/


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Curr. Op. in Plant Biology (2012): Epigenetic responses to stress: triple defense?

Curr. Op. in Plant Biology (2012):  Epigenetic responses to stress: triple defense? | Effectors and Plant Immunity | Scoop.it

Stressful conditions for plants can originate from numerous physical, chemical and biological factors, and plants have developed a plethora of survival strategies including developmental and morphological adaptations, specific signaling and defense pathways as well as innate and acquired immunity. While it has become clear in recent years that many stress responses involve epigenetic components, we are far from understanding the mechanisms and molecular interactions. Extending our knowledge is fundamental, not least for plant breeding and conservation biology. This review will highlight recent insights into epigenetic stress responses at the level of signaling, chromatin modification, and potentially heritable consequences.

 

Ruben Gutzat, Ortrun Mittelsten Scheid

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PLoS Pathogens (2012): The Cyclase-Associated Protein Cap1 Is Important for Proper Regulation of Infection-Related Morphogenesis in Magnaporthe oryzae

PLoS Pathogens (2012): The Cyclase-Associated Protein Cap1 Is Important for Proper Regulation of Infection-Related Morphogenesis in Magnaporthe oryzae | Effectors and Plant Immunity | Scoop.it

Surface recognition and penetration are critical steps in the infection cycle of many plant pathogenic fungi. In Magnaporthe oryzae, cAMP signaling is involved in surface recognition and pathogenesis. Deletion of the MAC1 adenylate cyclase gene affected appressorium formation and plant infection. In this study, we used the affinity purification approach to identify proteins that are associated with Mac1 in vivo. One of the Mac1-interacting proteins is the adenylate cyclase-associated protein named Cap1. CAP genes are well-conserved in phytopathogenic fungi but none of them have been functionally characterized. Deletion of CAP1 blocked the effects of a dominant RAS2 allele and resulted in defects in invasive growth and a reduced intracellular cAMP level. The Δcap1 mutant was defective in germ tube growth, appressorium formation, and formation of typical blast lesions. Cap1-GFP had an actin-like localization pattern, localizing to the apical regions in vegetative hyphae, at the periphery of developing appressoria, and in circular structures at the base of mature appressoria. Interestingly, Cap1, similar to LifeAct, did not localize to the apical regions in invasive hyphae, suggesting that the apical actin cytoskeleton differs between vegetative and invasive hyphae. Domain deletion analysis indicated that the proline-rich region P2 but not the actin-binding domain (AB) of Cap1 was responsible for its subcellular localization. Nevertheless, the AB domain of Cap1 must be important for its function because CAP1ΔAB only partially rescued the Δcap1 mutant. Furthermore, exogenous cAMP induced the formation of appressorium-like structures in non-germinated conidia in CAP1ΔAB transformants. This novel observation suggested that AB domain deletion may result in overstimulation of appressorium formation by cAMP treatment. Overall, our results indicated that CAP1 is important for the activation of adenylate cyclase, appressorium morphogenesis, and plant infection in M. oryzae. CAP1 may also play a role in feedback inhibition of Ras2 signaling when Pmk1 is activated.

 

Xiaoying Zhou, Haifeng Zhang, Guotian Li, Brian Shaw, Jin-Rong X

 

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allAfrica.com: South Africa: Another Strain of Deadly Wheat Fungus

Johannesburg — As the world's supply of staple grains grows tight, scientists are learning about the discovery in South Africa of yet another deadly variant of Ug99 stem rust, a virulent fungal disease that can devastate wheat crops within weeks.The world's top wheat scientists are gathering in Beijing, China, for a global symposium on the rapidly mutating disease, organized by the Borlaug Global Rust Initiative (BGRI). The discovery of the new variant brings the total number of new forms of Ug99 in South Africa to four, scientists at the forum told IRIN. "There are two possibilities for the [surfacing of] Ug99 variants in South Africa," said Zacharias Pretorius, professor of plant pathology at the University of the Free State, in South Africa. "Firstly, migration of the fungal spores by wind movement from countries to the north of us, where we have detected similar races [mutations]. Secondly, I believe that at least one of the four variants developed locally through mutation." Fortunately, Pretorius said, the wheat race that seems particularly susceptible to the new Ug99 variant is not very popular among consumers. Still, the emergence of this new rust variant is an indication of how virulent the fungus remains.

It also places the wheat fields in Australia, one of the world's major producers, under threat. Dave Hodson, a scientist with the Mexico-based International Maize and Wheat Improvement Centre (CIMMYT), points out that stem rust spores have travelled from South Africa to Australia three times before - the last time in 1973. When spores of the fungus travelled from South Africa to Australia in 1969, it caused outbreaks that destroyed hundreds of thousands of dollars of wheat.

 

 


Via Valerio Hoyos-Villegas
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Molecular Plant (2012): The Long-Sought-After Salicylic Acid Receptors

Molecular Plant (2012): The Long-Sought-After Salicylic Acid Receptors | Effectors and Plant Immunity | Scoop.it

The plant hormone salicylic acid (SA) plays a prominent role in modulating plant immune responses against diverse pathogens. SA also influences other physiological processes in plants, such as senescence-associated gene expression, basal thermogenesis, and seed germination (Vlot et al., 2009). Because of the critical role of SA in regulating plant immunity, growth, and development, there has been immense research about SA, which has resulted in the discovery of numerous plant genes involved in SA biosynthesis or signal transduction. One of the most notable findings was the identification of NPR1 (non-expressor of pathogenesis protein 1) (Cao et al., 1994; Delaney et al., 1995), a gene that encodes a master regulatory protein of SA-dependent defense responses and is a transcriptional co-activator of the TGA clade of bZIP transcription factors (transcription factors that contain basic region/leucine zipper motif)...

 

Elham Attarana and Sheng Yang He

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Nature News Blog: Researchers step up fight against wheat pathogens

Nature News Blog: Researchers step up fight against wheat pathogens | Effectors and Plant Immunity | Scoop.it

Researchers are putting up a strong fight against devastating wheat pathogens, and have made progress in tracking and controlling disease outbreaks helping to protect crops from East Africa to South Asia.But the wheat fields of central Asia, including China – the world’s largest wheat producer – are still vulnerable, agricultural scientist will warn at an international conference in Beijing next week.

 

Posted by Natasha Gilbert

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PLoS Genetics (2012): Comparative Analysis of the Genomes of Two Field Isolates of the Rice Blast Fungus Magnaporthe oryzae

PLoS Genetics (2012): Comparative Analysis of the Genomes of Two Field Isolates of the Rice Blast Fungus Magnaporthe oryzae | Effectors and Plant Immunity | Scoop.it

Rice blast caused by Magnaporthe oryzae is one of the most destructive diseases of rice worldwide. The fungal pathogen is notorious for its ability to overcome host resistance. To better understand its genetic variation in nature, we sequenced the genomes of two field isolates, Y34 and P131. In comparison with the previously sequenced laboratory strain 70-15, both field isolates had a similar genome size but slightly more genes. Sequences from the field isolates were used to improve genome assembly and gene prediction of 70-15. Although the overall genome structure is similar, a number of gene families that are likely involved in plant-fungal interactions are expanded in the field isolates. Genome-wide analysis on asynonymous to synonymous nucleotide substitution rates revealed that many infection-related genes underwent diversifying selection. The field isolates also have hundreds of isolate-specific genes and a number of isolate-specific gene duplication events. Functional characterization of randomly selected isolate-specific genes revealed that they play diverse roles, some of which affect virulence. Furthermore, each genome contains thousands of loci of transposon-like elements, but less than 30% of them are conserved among different isolates, suggesting active transposition events in M. oryzae. A total of approximately 200 genes were disrupted in these three strains by transposable elements. Interestingly, transposon-like elements tend to be associated with isolate-specific or duplicated sequences. Overall, our results indicate that gain or loss of unique genes, DNA duplication, gene family expansion, and frequent translocation of transposon-like elements are important factors in genome variation of the rice blast fungus.

 

Minfeng Xue, Jun Yang, Zhigang Li, Songnian Hu, Nan Yao, Ralph A. Dean, Wensheng Zhao, Mi Shen, Haiwang Zhang, Chao Li, Liyuan Liu, Lei Cao, Xiaowen Xu, Yunfei Xing, Tom Hsiang, Ziding Zhang, Jin-Rong Xu, You-Liang Peng

 

 

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