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Effectors and Plant Immunity
Strategies of plant defense and microbe attacks
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Rescooped by Nicolas Denancé from Plant-microbe interaction
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Scientific Reports (2012): ImprimatinC1, a novel plant immune-priming compound, functions as a partial agonist of salicylic acid

Scientific Reports (2012): ImprimatinC1, a novel plant immune-priming compound, functions as a partial agonist of salicylic acid | Effectors and Plant Immunity | Scoop.it

Plant activators are agrochemicals that protect crops from pathogens. They confer durable resistance to a broad range of diseases by activating intrinsic immune mechanisms in plants. To obtain leads regarding useful compounds, we have screened a chemical library using an established method that allows selective identification of immune-priming compounds. Here, we report the characterisation of one of the isolated chemicals, imprimatinC1, and its structural derivative imprimatinC2. ImprimatinC1 functions as a weak analogue of salicylic acid (SA) and activates the expression of defence-related genes. However, it lacks antagonistic activity toward jasmonic acid. Structure-activity relationship analysis suggests that imprimatinC1 and C2 can be metabolised to 4-chlorobenzoic acid and 3,4-chlorobenzoic acid, respectively, to function in Arabidopsis. We also found that imprimatinC1 and C2 and their potential functional metabolites acted as partial agonists of SA. Thus, imprimatinC compounds could be useful tools for dissecting SA-dependent signal transduction pathways.

 

Noutoshi Y, Jikumaru Y, Kamiya Y, Shirasu K.

 


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PLOS Pathogens: Genome Analyses of an Aggressive and Invasive Lineage of the Irish Potato Famine Pathogen

PLOS Pathogens: Genome Analyses of an Aggressive and Invasive Lineage of the Irish Potato Famine Pathogen | Effectors and Plant Immunity | Scoop.it

Pest and pathogen losses jeopardise global food security and ever since the 19th century Irish famine, potato late blight has exemplified this threat. The causal oomycete pathogen, Phytophthora infestans, undergoes major population shifts in agricultural systems via the successive emergence and migration of asexual lineages. The phenotypic and genotypic bases of these selective sweeps are largely unknown but management strategies need to adapt to reflect the changing pathogen population. Here, we used molecular markers to document the emergence of a lineage, termed 13_A2, in the European P. infestans population, and its rapid displacement of other lineages to exceed 75% of the pathogen population across Great Britain in less than three years. We show that isolates of the 13_A2 lineage are among the most aggressive on cultivated potatoes, outcompete other aggressive lineages in the field, and overcome previously effective forms of plant host resistance. Genome analyses of a 13_A2 isolate revealed extensive genetic and expression polymorphisms particularly in effector genes. Copy number variations, gene gains and losses, amino-acid replacements and changes in expression patterns of disease effector genes within the 13_A2 isolate likely contribute to enhanced virulence and aggressiveness to drive this population displacement. Importantly, 13_A2 isolates carry intact and in planta induced Avrblb1, Avrblb2 and Avrvnt1 effector genes that trigger resistance in potato lines carrying the corresponding R immune receptor genes Rpi-blb1, Rpi-blb2, and Rpi-vnt1.1. These findings point towards a strategy for deploying genetic resistance to mitigate the impact of the 13_A2 lineage and illustrate how pathogen population monitoring, combined with genome analysis, informs the management of devastating disease epidemics.

 

David E. L. Cooke, Liliana M. Cano, Sylvain Raffaele, Ruairidh A. Bain, Louise R. Cooke, Graham J. Etherington, Kenneth L. Deahl, Rhys A. Farrer, Eleanor M. Gilroy, Erica M. Goss, Niklaus J. Grünwald, Ingo Hein, Daniel MacLean, James W. McNicol, Eva Randall, Ricardo F. Oliva, Mathieu A. Pel, David S. Shaw, Julie N. Squires, Moray C. Taylor, Vivianne G. A. A. Vleeshouwers, Paul R. J. Birch, Alison K. Lees, Sophien Kamoun

 

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J. Exp. Bot. (2012): On the move: Induced resistance in monocots

J. Exp. Bot. (2012): On the move: Induced resistance in monocots | Effectors and Plant Immunity | Scoop.it

Although plants possess an arsenal of constitutive defences such as structural barriers and preformed antimicrobial defences, many attackers are able to overcome the pre-existing defence layers. In response, a range of inducible plant defences is set up to battle these pathogens. These mechanisms, commonly integrated as induced resistance (IR), control pathogens and pests by the activation of specific defence pathways. IR mechanisms have been extensively studied in the Dicotyledoneae, whereas knowledge of IR in monocotyledonous plants, including the globally important graminaceous crop plants, is elusive. Considering the potential of IR for sustainable agriculture and the recent advances in monocot genomics and biotechnology, IR in monocots is an emerging research field. In the following, current facts and trends concerning basal immunity, and systemic acquired/induced systemic resistance in the defence of monocots against pathogens and herbivores will be summarized.

 

Dirk Balmer, Chantal Planchamp, and Brigitte Mauch-Mani

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PLOS Genetics: The Non-Flagellar Type III Secretion System Evolved from the Bacterial Flagellum and Diversified into Host-Cell Adapted Systems

PLOS Genetics: The Non-Flagellar Type III Secretion System Evolved from the Bacterial Flagellum and Diversified into Host-Cell Adapted Systems | Effectors and Plant Immunity | Scoop.it

Type 3 secretion systems (T3SSs) are essential components of two complex bacterial machineries: the flagellum, which drives cell motility, and the non-flagellar T3SS (NF-T3SS), which delivers effectors into eukaryotic cells. Yet the origin, specialization, and diversification of these machineries remained unclear. We developed computational tools to identify homologous components of the two systems and to discriminate between them. Our analysis of >1,000 genomes identified 921 T3SSs, including 222 NF-T3SSs. Phylogenomic and comparative analyses of these systems argue that the NF-T3SS arose from an exaptation of the flagellum, i.e. the recruitment of part of the flagellum structure for the evolution of the new protein delivery function. This reconstructed chronology of the exaptation process proceeded in at least two steps. An intermediate ancestral form of NF-T3SS, whose descendants still exist in Myxococcales, lacked elements that are essential for motility and included a subset of NF-T3SS features. We argue that this ancestral version was involved in protein translocation. A second major step in the evolution of NF-T3SSs occurred via recruitment of secretins to the NF-T3SS, an event that occurred at least three times from different systems. In rhizobiales, a partial homologous gene replacement of the secretin resulted in two genes of complementary function. Acquisition of a secretin was followed by the rapid adaptation of the resulting NF-T3SSs to multiple, distinct eukaryotic cell envelopes where they became key in parasitic and mutualistic associations between prokaryotes and eukaryotes. Our work elucidates major steps of the evolutionary scenario leading to extant NF-T3SSs. It demonstrates how molecular evolution can convert one complex molecular machine into a second, equally complex machine by successive deletions, innovations, and recruitment from other molecular systems.

 

Sophie S. Abby, Eduardo P. C. Rocha

 

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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/


Via Anne-Sophie Roy
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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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Science (2012): Natural Enemies Drive Geographic Variation in Plant Defenses

Science (2012): Natural Enemies Drive Geographic Variation in Plant Defenses | Effectors and Plant Immunity | Scoop.it

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

 

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

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Nature (2012): Plant science - The chestnut resurrection

Nature (2012): Plant science - The chestnut resurrection | Effectors and Plant Immunity | Scoop.it

Once king of eastern forests, the American chestnut was wiped out by blight. Now it is poised to rise again. “They're hard to breed and easy to kill,” says plant pathologist Fred Hebard as he attacks a 2-metre-tall chestnut tree in southwest Virginia. Hebard bores a hole in the bark and squeezes a mash of orange fungus into the wood. The tree is a hybrid of the Chinese and American chestnut species, and Hebard hopes that it has enough resistance genes to keep the fungus — called chestnut blight — at bay. If so, the hybrid could help to resurrect a long-gone icon.

 

Helen Thompson

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PLOS Pathogens (2012): A Population Genomics Perspective on the Emergence and Adaptation of New Plant Pathogens in Agro-Ecosystems

PLOS Pathogens (2012): A Population Genomics Perspective on the Emergence and Adaptation of New Plant Pathogens in Agro-Ecosystems | Effectors and Plant Immunity | Scoop.it

Plants and pathogens evolve in response to each other. This co-evolutionary arms race is fueled by genetic variation underlying the recognition of pathogen proteins by the host and the defeat of host defenses by the pathogen. Together with new mutations, genetic diversity in populations of both the host and pathogen represent a pool of possible variants to maintain adaptation via natural selection.Drastic changes in genetic diversity in crop species have occurred as a consequence of domestication. Whether changes in the genetic composition of these host populations also have affected genetic diversity in pathogen species is, so far, poorly understood. Advances in comparative genomics and population genomic approaches open new avenues to study adaptive processes in plant pathogens and to infer the impact of agro-ecosystems on the evolution of pathogen populations. Here we summarize new insights gained from comparative genome studies and population genomics in host-pathogen systems.

 

Eva H. Stukenbrock, Thomas Bataillon

 

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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


Via Freddy Monteiro
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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


Via Suayib Üstün
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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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