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Rescooped by Dr.donkey from Plant pathogens and pests
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Characterization of the Largest Effector Gene Cluster of Ustilago maydis

Characterization of the Largest Effector Gene Cluster of Ustilago maydis | Plant immunity | Scoop.it

In the genome of the biotrophic plant pathogen Ustilago maydis, many of the genes coding for secreted protein effectors modulating virulence are arranged in gene clusters. The vast majority of these genes encode novel proteins whose expression is coupled to plant colonization. The largest of these gene clusters, cluster 19A, encodes 24 secreted effectors. Deletion of the entire cluster results in severe attenuation of virulence. Here we present the functional analysis of this genomic region. We show that a 19A deletion mutant behaves like an endophyte, i.e. is still able to colonize plants and complete the infection cycle. However, tumors, the most conspicuous symptoms of maize smut disease, are only rarely formed and fungal biomass in infected tissue is significantly reduced. The generation and analysis of strains carrying sub-deletions identified several genes significantly contributing to tumor formation after seedling infection. Another of the effectors could be linked specifically to anthocyanin induction in the infected tissue. As the individual contributions of these genes to tumor formation were small, we studied the response of maize plants to the whole cluster mutant as well as to several individual mutants by array analysis. This revealed distinct plant responses, demonstrating that the respective effectors have discrete plant targets. We propose that the analysis of plant responses to effector mutant strains that lack a strong virulence phenotype may be a general way to visualize differences in effector function.


Via Christophe Jacquet
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Targeted gene disruption of OsCERK1 reveals its indispensable role in chitin perception and involvement in the peptidoglycan response and immunity in rice

OsCERK1 is a rice receptor-like kinase that mediates the signal of a fungal cell wall component, chitin, by coordinating with a lysin motif (LysM)-containing protein, CEBiP. To further elucidate the function of OsCERK1 in the defense response, we disrupted OsCERK1 using an Agrobacterium-mediated gene targeting system based on homologous recombination. In OsCERK1-disrupted lines, the generation of hydrogen peroxide and the alteration of gene expression in response to a chitin oligomer were completely abolished. The OsCERK1-disrupted lines also showed lowered responsiveness to a bacterial cell wall component, peptidoglycan. Yeast two-hybrid analysis indicated that OsCERK1 interacts with the LysM-containing proteins, LYP4 and LYP6, which are known to participate in the peptidoglycan response in rice. Observation of the infection behavior of rice blast fungus (Magnaporthe oryzae) revealed that disruption of OsCERK1 led to increased hyphal growth in leaf sheath cells. GFP-tagged OsCERK1 was localized around the primary infection hyphae. These results demonstrate that OsCERK1 is indispensable for chitin perception and participates in innate immunity in rice, and also mediates the peptidoglycan response. It is also suggested that OsCERK1 mediates the signaling pathways of both fungal and bacterial molecular patterns by interacting with different LysM-containing receptor-like proteins.


Via Christophe Jacquet
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Targeted gene disruption of OsCERK1 reveals its indispensable role in chitin perception and involvement in the peptidoglycan response and immunity in rice

Targeted gene disruption of OsCERK1 reveals its indispensable role in chitin perception and involvement in the peptidoglycan response and immunity in rice | Plant immunity | Scoop.it

OsCERK1 is a rice receptor-like kinase that mediates the signal of a fungal cell wall component, chitin, by coordinating with a lysin motif (LysM)-containing protein, CEBiP. To further elucidate the function of OsCERK1 in the defense response, we disrupted OsCERK1. In OsCERK1-disrupted lines, the generation of hydrogen peroxide and the alteration of gene expression in response to a chitin oligomer were completely abolished. The OsCERK1-disrupted lines also showed lowered responsiveness to a bacterial cell wall component, peptidoglycan. Yeast two-hybrid analysis indicated that OsCERK1 interacts with the LysM-containing proteins, LYP4 and LYP6, which are known to participate in the peptidoglycan response in rice. Observation of the infection behavior of rice blast fungus (Magnaporthe oryzae) revealed that disruption of OsCERK1 led to increased hyphal growth in leaf sheath cells. GFP-tagged OsCERK1 was localized around the primary infection hyphae. These results demonstrate that OsCERK1 is indispensable for chitin perception and participates in innate immunity in rice, and also mediates the peptidoglycan response. It is also suggested that OsCERK1 mediates the signaling pathways of both fungal and bacterial molecular patterns by interacting with different LysM-containing receptor-like proteins.


Via Elsa Ballini
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Plant ubiquitin ligases as signaling hubs : Nature Structural & Molecular Biology : Nature Publishing Group

Plant ubiquitin ligases as signaling hubs : Nature Structural & Molecular Biology : Nature Publishing Group | Plant immunity | Scoop.it
The past decade has witnessed an explosion in the identification of ubiquitin-ligase complexes as the missing receptors for important small-molecule hormones regulating plant growth and development. These breakthroughs were initiated by genetic approaches, with structural analysis providing mechanistic insights into how hormone perception and signaling are coupled to protein ubiquitination. Although there are still many unknowns, plants have imparted valuable lessons about the pharmacology of ubiquitin modification.

Via Suayib Üstün
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Molecular Cellular Proteomics: Profiling the secretome and extracellular proteome of the potato late blight pathogen Phytophthora infestans (2014)

Molecular Cellular Proteomics: Profiling the secretome and extracellular proteome of the potato late blight pathogen Phytophthora infestans (2014) | Plant immunity | Scoop.it

Oomycetes are filamentous organisms that cause notorious diseases, several of which have a high economic impact. Well known is Phytophthora infestans, the causal agent of potato late blight. Previously, in silico analyses of the genome and transcriptome of P. infestans resulted in the annotation of a large number of genes encoding proteins with an N-terminal signal peptide. This set is collectively referred to as the secretome and comprises proteins involved in, for example, cell wall growth and modification, proteolytic processes and the promotion of successful invasion of plant cells. So far, proteomic profiling in oomycetes was primarily focussed on subcellular, intracellular or cell wall fractions; the extracellular proteome has not been studied systematically. Here we present the first comprehensive characterization of the in vivo secretome and extracellular proteome of P. infestans. We have used mass spectrometry to analyse P. infestans proteins present in seven different growth media with mycelial cultures and this resulted in the consistent identification of over two hundred proteins. Gene ontology classification pinpointed proteins involved in cell wall modifications, pathogenesis, defense responses and proteolytic processes. Moreover, we found members of the RXLR and CRN effector families as well as several proteins lacking an obvious signal peptide. The latter were confirmed to be bona fide extracellular proteins and this suggests that, similar to other organisms, oomycetes exploit non-conventional secretion mechanisms to transfer certain proteins to the extracellular environment.


Via Kamoun Lab @ TSL, Niklaus Grunwald, Jim Alfano
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Spatiotemporal Production of Reactive Oxygen Species by NADPH Oxidase Is Critical for Tapetal Programmed Cell Death and Pollen Development in Arabidopsis

Spatiotemporal Production of Reactive Oxygen Species by NADPH Oxidase Is Critical for Tapetal Programmed Cell Death and Pollen Development in Arabidopsis | Plant immunity | Scoop.it

Male sterility in angiosperms has wide applications in agriculture, particularly in hybrid crop breeding and gene flow control. Microspores develop adjacent to the tapetum, a layer of cells that provides nutrients for pollen development and materials for pollen wall formation. Proper pollen development requires programmed cell death (PCD) of the tapetum, which requires transcriptional cascades and proteolytic enzymes. Reactive oxygen species (ROS) also affect tapetal PCD, and failures in ROS scavenging cause male sterility. However, many aspects of tapetal PCD remain unclear, including what sources generate ROS, whether ROS production has a temporal pattern, and how the ROS-producing system interacts with the tapetal transcriptional network. We report here that stage-specific expression of NADPH oxidases in the Arabidopsis thalianatapetum contributes to a temporal peak of ROS production. Genetic interference with the temporal ROS pattern, by manipulating RESPIRATORY-BURST OXIDASE HOMOLOG (RBOH) genes, affected the timing of tapetal PCD and resulted in aborted male gametophytes. We further show that the tapetal transcriptional network regulates RBOH expression, indicating that the temporal pattern of ROSproduction intimately connects to other signaling pathways regulated by the tapetal transcriptional network to ensure the proper timing of tapetal PCD.


Via Jennifer Mach
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Large-Scale Psychological Differences Within China Explained by Rice Versus Wheat Agriculture

Cross-cultural psychologists have mostly contrasted East Asia with the West. However, this study shows that there are major psychological differences within China. We propose that a history of farming rice makes cultures more interdependent, whereas farming wheat makes cultures more independent, and these agricultural legacies continue to affect people in the modern world. We tested 1162 Han Chinese participants in six sites and found that rice-growing southern China is more interdependent and holistic-thinking than the wheat-growing north. To control for confounds like climate, we tested people from neighboring counties along the rice-wheat border and found differences that were just as large. We also find that modernization and pathogen prevalence theories do not fit the data.


Via Jennifer Mach
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Jennifer Mach's curator insight, May 8, 5:16 PM

Not strictly cell biology, but an interesting study on the effects of crop domestication. "Perspective" article here:

http://www.sciencemag.org/content/344/6184/593.summary

Rescooped by Dr.donkey from Emerging Research in Plant Cell Biology
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Science: Paired Plant Immune Receptors (2014)

Science: Paired Plant Immune Receptors (2014) | Plant immunity | Scoop.it

Plants are constantly interpreting microbial signals from potential pathogens and potential commensals or mutualists. Because plants have no circulating cells dedicated to this task, every plant cell must, in principle, recognize any microbe as friend, foe, or irrelevant bystander. That tall order is mediated by an array of innate immune system receptors: pattern-recognition receptors outside the plant cell and nucleotide-binding oligomerization domain (NOD)–like receptors (NLRs) inside the cell. Despite their importance for plant health, how NLRs function mechanistically has remained obscure. On page 299 of this issue, Williams et al. (1) reveal a role for heterodimerization between NLRs and show how the rather limited NLR repertoire of any plant genome might be enhanced by combinatorial diversity.

 

Marc T. Nishimura, Jeffery L. Dangl


Via Nicolas Denancé, Jennifer Mach
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Decreased abundance of type III secretion system-inducing signals in Arabidopsis mkp1 enhances resistance against Pseudomonas syringae

Decreased abundance of type III secretion system-inducing signals in Arabidopsis mkp1 enhances resistance against Pseudomonas syringae | Plant immunity | Scoop.it

Abstract

Genes encoding the virulence-promoting type III secretion system (T3SS) in phytopathogenic bacteria are induced at the start of infection, indicating that recognition of signals from the host plant initiates this response. However, the precise nature of these signals and whether their concentrations can be altered to affect the biological outcome of host–pathogen interactions remain speculative. Here we use a metabolomic comparison of resistant and susceptible genotypes to identify plant-derived metabolites that induce T3SS genes in Pseudomonas syringae pv tomato DC3000 and report that mapk phosphatase 1 (mkp1), an Arabidopsis mutant that is more resistant to bacterial infection, produces decreased levels of these bioactive compounds. Consistent with these observations, T3SS effector expression and delivery by DC3000 was impaired when infecting the mkp1 mutant. The addition of bioactive metabolites fully restored T3SS effector delivery and suppressed the enhanced resistance in the mkp1 mutant. Pretreatment of plants with pathogen-associated molecular patterns (PAMPs) to induce PAMP-triggered immunity (PTI) also restricts T3SS effector delivery and enhances resistance by unknown mechanisms, and the addition of the bioactive metabolites similarly suppressed both aspects of PTI. Together, these results demonstrate that DC3000 perceives multiple signals derived from plants to initiate its T3SS and that the level of these host-derived signals impacts bacterial pathogenesis.


Via Suayib Üstün, Jim Alfano, Freddy Monteiro
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Allele-mining of rice blast resistance genes at AC134922 locus

Allele-mining of rice blast resistance genes at AC134922 locus | Plant immunity | Scoop.it

The AC134922 locus is one of the most rapidly evolving nucleotide binding site–leucine-rich repeat (NBS-LRR) gene family in rice genome. Six rice blast resistance (R) genes have been cloned from this locus and other two resistance candidate genes, Pi34 and Pi47, are also mapped to this complex locus. Therefore, it seems that more functional R genes could be identified from this locus. In this study, we cloned 22 genes from 12 cultivars based on allele-mining strategy at this locus and identified 6 rice blast R genes with 4 of them recognizing more than one isolates. Our result suggests that gene stacking might be the evolutionary strategy for complex gene locus to interact with rapidly evolving pathogens, which might provide a potential way for the cloning of durable resistance genes. Moreover, the mosaic structure and ambiguous ortholog/paralog relationships of these homologous genes, caused by frequent recombination and gene conversion, indicate that multiple alleles of this complex locus may serve as a reservoir for the evolutionary novelty of these R genes.


Via Elsa Ballini
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The Arabidopsis thaliana LYSM-CONTAINING RECEPTOR-LIKE KINASE 3 regulates the cross talk between immunity and abscisic acid responses.

The Arabidopsis thaliana LYSM-CONTAINING RECEPTOR-LIKE KINASE 3 regulates the cross talk between immunity and abscisic acid responses. | Plant immunity | Scoop.it

Transmembrane receptor-like kinases characterized by the presence of one or more LysM domains in the extracytoplasmic portion (LysM-containing receptor-like kinase, LYKs) mediate recognition of symbiotic and pathogenic microorganisms in plants. The Arabidopsis thaliana genome encodes five putative LYKs; among them, LYSM RLK1/CHITIN ELICITOR RECEPTOR KINASE 1 is required for response to chitin and peptidoglycan, and AtLYK4 contributes to chitin perception. More recently, AtLYK3 has been shown to be required for full repression, mediated by Nod factors, of Arabidopsis innate immune responses. In this work we show that AtLYK3 negatively regulates also basal expression of defence genes and resistance to Botrytis cinerea and Pectobacterium carotovorum infection. Enhanced resistance of atlyk3 mutants requires PHYTOALEXIN-DEFICIENT 3, which is crucial for camalexin biosynthesis. The expression of AtLYK3 is strongly repressed by elicitors and fungal infection, and is induced by the hormone abscisic acid (ABA), which has a negative impact on resistance against B. cinerea and P. carotovorum. Plants lacking a functional AtLYK3 also show reduced physiological responses to ABA, and are partially resistant to ABA-induced inhibition of PAD3 expression. These results indicate that AtLYK3 is important for the cross-talk between signaling pathways activated by ABA and pathogens.


Via Olivier ANDRE, Christophe Jacquet, Guogen Yang
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The Reference Genome Sequence of Saccharomyces cerevisiae: Then and Now

The Reference Genome Sequence of Saccharomyces cerevisiae: Then and Now | Plant immunity | Scoop.it

The genome of the budding yeast Saccharomyces cerevisiae was the first completely sequenced from a eukaryote. It was released in 1996 as the work of a worldwide effort of hundreds of researchers. In the time since, the yeast genome has been intensively studied by geneticists, molecular biologists, and computational scientists all over the world. Maintenance and annotation of the genome sequence have long been provided by the Saccharomyces Genome Database, one of the original model organism databases. To deepen our understanding of the eukaryotic genome, the S. cerevisiae strain S288C reference genome sequence was updated recently in its first major update since 1996. The new version, called “S288C 2010,” was determined from a single yeast colony using modern sequencing technologies and serves as the anchor for further innovations in yeast genomic science.


Via Francis Martin
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The Arabidopsis thaliana LYSM-CONTAINING RECEPTOR-LIKE KINASE 3 regulates the cross talk between immunity and abscisic acid responses.

The Arabidopsis thaliana LYSM-CONTAINING RECEPTOR-LIKE KINASE 3 regulates the cross talk between immunity and abscisic acid responses. | Plant immunity | Scoop.it

Transmembrane receptor-like kinases characterized by the presence of one or more LysM domains in the extracytoplasmic portion (LysM-containing receptor-like kinase, LYKs) mediate recognition of symbiotic and pathogenic microorganisms in plants. The Arabidopsis thaliana genome encodes five putative LYKs; among them, LYSM RLK1/CHITIN ELICITOR RECEPTOR KINASE 1 is required for response to chitin and peptidoglycan, and AtLYK4 contributes to chitin perception. More recently, AtLYK3 has been shown to be required for full repression, mediated by Nod factors, of Arabidopsis innate immune responses. In this work we show that AtLYK3 negatively regulates also basal expression of defence genes and resistance to Botrytis cinerea and Pectobacterium carotovorum infection. Enhanced resistance of atlyk3 mutants requires PHYTOALEXIN-DEFICIENT 3, which is crucial for camalexin biosynthesis. The expression of AtLYK3 is strongly repressed by elicitors and fungal infection, and is induced by the hormone abscisic acid (ABA), which has a negative impact on resistance against B. cinerea and P. carotovorum. Plants lacking a functional AtLYK3 also show reduced physiological responses to ABA, and are partially resistant to ABA-induced inhibition of PAD3 expression. These results indicate that AtLYK3 is important for the cross-talk between signaling pathways activated by ABA and pathogens.


Via Olivier ANDRE, Christophe Jacquet
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Characterization of the Largest Effector Gene Cluster of Ustilago maydis

Characterization of the Largest Effector Gene Cluster of Ustilago maydis | Plant immunity | Scoop.it

In the genome of the biotrophic plant pathogen Ustilago maydis, many of the genes coding for secreted protein effectors modulating virulence are arranged in gene clusters. The vast majority of these genes encode novel proteins whose expression is coupled to plant colonization. The largest of these gene clusters, cluster 19A, encodes 24 secreted effectors. Deletion of the entire cluster results in severe attenuation of virulence. Here we present the functional analysis of this genomic region. We show that a 19A deletion mutant behaves like an endophyte, i.e. is still able to colonize plants and complete the infection cycle. However, tumors, the most conspicuous symptoms of maize smut disease, are only rarely formed and fungal biomass in infected tissue is significantly reduced. The generation and analysis of strains carrying sub-deletions identified several genes significantly contributing to tumor formation after seedling infection. Another of the effectors could be linked specifically to anthocyanin induction in the infected tissue. As the individual contributions of these genes to tumor formation were small, we studied the response of maize plants to the whole cluster mutant as well as to several individual mutants by array analysis. This revealed distinct plant responses, demonstrating that the respective effectors have discrete plant targets. We propose that the analysis of plant responses to effector mutant strains that lack a strong virulence phenotype may be a general way to visualize differences in effector function.


Via Suayib Üstün
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Microorganism and filamentous fungi drive evolution of plant synapses

Microorganism and filamentous fungi drive evolution of plant synapses | Plant immunity | Scoop.it
In the course of plant evolution, there is an obvious trend toward an increased complexity of plant bodies, as well as an increased sophistication of plant behavior and communication. Phenotypic plasticity of plants is based on the polar auxin transport machinery that is directly linked with plant sensory systems impinging on plant behavior and adaptive responses. Similar to the emergence and evolution of eukaryotic cells, evolution of land plants was also shaped and driven by infective and symbiotic microorganisms. These microorganisms are the driving force behind the evolution of plant synapses and other neuronal aspects of higher plants; this is especially pronounced in the root apices. Plant synapses allow synaptic cell-cell communication and coordination in plants, as well as sensory-motor integration in root apices searching for water and mineral nutrition. These neuronal aspects of higher plants are closely linked with their unique ability to adapt to environmental changes.

Via Jean-Michel Ané, Christophe Jacquet
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Genotyping and development of single-nucleotide polymorphism (SNP) markers associated with blast resistance genes in rice using GoldenGate assay

Genotyping and development of single-nucleotide polymorphism (SNP) markers associated with blast resistance genes in rice using GoldenGate assay | Plant immunity | Scoop.it

In the present study, Illumina GoldenGate assay was used to validate and genotype SNPs in a set of six major rice blast resistance genes: Pi-ta, Piz(t), Pi54, Pi9, Pi5(1)and Pib. All the selected SNPs loci (96) were genotyped successfully in 92 rice lines with an overall genotype call rate of 92.0 % and minimum GenTrain cutoff score of ≥0.448. Minor allele frequency ranged from 0.01 to 0.49 and has good differentiating power for distinguishing different rice accessions. SNPs markers were validated in a set of 92 rice lines and converted into CAPS markers which can be used in blast resistance breeding programme.


Via Elsa Ballini
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Interaction specificity and coexpression of rice NPR1 homologs 1 and 3 (NH1 and NH3), TGA transcription factors and Negative Regulator of Resistance (NRR) proteins

Interaction specificity and coexpression of rice NPR1 homologs 1 and 3 (NH1 and NH3), TGA transcription factors and Negative Regulator of Resistance (NRR) proteins | Plant immunity | Scoop.it

Background

The nonexpressor of pathogenesis-related genes 1, NPR1 (also known as NIM1 and SAI1), is a key regulator of SA-mediated systemic acquired resistance (SAR) in Arabidopsis. In rice, the NPR1 homolog 1 (NH1) interacts with TGA transcriptional regulators and the Negative Regulator of Resistance (NRR) protein to modulate the SAR response. Though five NPR1 homologs (NHs) have been identified in rice, only NH1 and NH3 enhance immunity when overexpressed. To understand why NH1 and NH3, but not NH2, NH4, or NH5, contribute to the rice immune response, we screened TGA transcription factors and NRR-like proteins for interactions specific to NH1 and NH3. We also examined their co-expression patterns using publicly available microarray data.

Results

We tested five NHs, four NRR homologs (RHs), and 13 rice TGA proteins for pair-wise protein interactions using yeast two-hybrid (Y2H) and split YFP assays. A survey of 331 inter-family interactions revealed a broad, complex protein interaction network. To investigate preferred interaction partners when all three families of proteins were present, we performed a bridged split YFP assay employing YFPN-fused TGA, YFPC-fused RH, and NH proteins without YFP fusions. We found 64 tertiary interactions mediated by NH family members among the 120 sets we examined. In the yeast two-hybrid assay, each NH protein was capable of interacting with most TGA and RH proteins. In the split YFP assay, NH1 was the most prevalent interactor of TGA and RH proteins, NH3 ranked the second, and NH4 ranked the third. Based on their interaction with TGA proteins, NH proteins can be divided into two subfamilies: NH1, NH2, and NH3 in one family and NH4 and NH5 in the other.

In addition to evidence of overlap in interaction partners, co-expression analyses of microarray data suggest a correlation between NH1 and NH3 expression patterns, supporting their common role in rice immunity. However, NH3 is very tightly co-expressed with RH1 and RH2, while NH1 is strongly, inversely co-expressed with RH proteins, representing a difference between NH1 and NH3 expression patterns.

Conclusions

Our genome-wide surveys reveal that each rice NH protein can partner with many rice TGA and RH proteins and that each NH protein prefers specific interaction partners. NH1 and NH3 are capable of interacting strongly with most rice TGA and RH proteins, whereas NH2, NH4, and NH5 have weaker, limited interaction with TGA and RH proteins in rice cells. We have identified rTGA2.1, rTGA2.2, rTGA2.3, rLG2, TGAL2 and TGAL4 proteins as the preferred partners of NH1 and NH3, but not NH2, NH4, or NH5. These TGA proteins may play an important role in NH1- and NH3-mediated immune responses. In contrast, NH4 and NH5 preferentially interact with TGAL5, TGAL7, TGAL8 and TGAL9, which are predicted to be involved in plant development.

The

 

 


Via Christophe Jacquet
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Network Modeling to Understand Plant Immunity -

Network Modeling to Understand Plant Immunity - | Plant immunity | Scoop.it

Deciphering the networks that underpin complex biological processes using experimental data remains a significant, but promising, challenge, a task made all the harder by the added complexity of host-pathogen interactions. The aim of this article is to review the progress in understanding plant immunity made so far by applying network modeling algorithms and to show how this computational/mathematical strategy is facilitating a systems view of plant defense. We review the different types of network modeling that have been used, the data required, and the type of insight that such modeling can provide. We discuss the current challenges in modeling the regulatory networks that underlie plant defense and the future developments that may help address these challenges.


Via Christophe Jacquet
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PlantVillage: Keeping Up With The Plant Destroyers (2014)

PlantVillage: Keeping Up With The Plant Destroyers (2014) | Plant immunity | Scoop.it

Readers of PlantVillage who visited popular pages like the one on tomato late blight would have come across the term “oomycetes” and probably wondered what in the world is an oomycete? It’s the taxon of microbes that groups many plant pathogens such as Phytophthora, Pythium, and the downy mildews. These are destructive pathogens of plants. Phytophthora, which stems from Greek words meaning plant-destroyer, is a diverse group of plant pathogens with over 100 species known to science . It includes the infamous Irish potato famine pathogen Phytophthora infestans. When this pathogen reached Ireland in the 1840s, it triggered famine and mayhem with one million people dead and another million forced to leave the island. Today, the late blight disease caused by P. infestans threatens not only tomatoes and potatoes in your gardens but also commercial and subsistence farming worldwide. Matt Fisher, Sarah Gurr and their colleagues recently estimated that losses due to late blight add up to enough calories to feed hundreds of millions of people.

 

So what are these oomycetes that are so feared by gardeners and farmers alike? Traditionally oomycetes were thought to be fungi (yeasts, molds and mushrooms). They are not. Modern methods of evolutionary analyses, known as phylogenetics, have cemented the view that oomycetes are only distant relatives of the fungi. In fact, fungi are more closely related to you and I than they are to the oomycetes. Oomycete biologists like to quip “bats are not birds, dolphins are not fish, and oomycetes are not fungi.” In fact, oomycetes turned out to have unexpected marine cousins in brown algae (kelp) and diatoms in a grouping known as the heterokonts. Oomycetes form a very deep branch in the tree of life and may have evolved from marine parasitic microorganisms. Just a few months ago, while I was visiting Christine Strullu-Derrien and Paul Kenrick at the Natural History Museum in London, I had the amazing opportunity to hold a fossil oomycete that is 300 million year old. Already in those ancient times, oomycetes were successful colonizers of plants and may even have been parasitic.

 

But evolution is a complicated process. More often than widely assumed, it proceeded as a reticulate network rather than a straight line. One example is the transfer of genes from one organism to another. This process, known as horizontal or lateral gene transfer, has occurred frequently in bacteria but is not as well documented in more complex organisms like oomycetes and fungi. Nonetheless, Tom Richard and colleagues at Exeter University reported that oomycetes have at some point in their evolution acquired genes from fungi. Whether this took place hundreds million years ago or more recently is not yet resolved. But as Tom likes to say “oomycetes are 99% not fungi”. How this phenomenon has contributed to the evolution of oomycetes into destructive plant pathogens is an interesting research topic.

 

But why all the misery? Why are oomycetes the scourge of farmers worldwide? The truth is, although Phytophthora are astonishing plant killers that can wipe out crops in days, the secret of their success is their ability to rapidly adapt to resistant plant varieties. Just like the constantly morphing flu virus, the potato blight pathogen and its relatives continuously spawn new races adapted to the resistant varieties released by plant breeders and even occasionally to new host plants. Like Lewis Carroll’s fictional Red Queen, plant breeders and biotechnologists only hope is to strenuously run to keep in the same place. If only we could produce resistant varieties more often then perhaps we’ll have a chance to outrace the ever-evolving blight pathogen.

 

So while you lament your blighted potatoes and your dying tomatoes, take a moment to ponder over the awesome parasite that’s making your vegetable garden look so gloomy. That microbe has already colonized plants way before humans emerged on earth. And for hundreds of millions of years it has kept on changing, evolving, and adapting ensuring its uninterrupted survival on an astonishing array of plant species and varieties. When humans domesticated plants, it could not resist the offering and adopted the crops as its new hosts. Ultimately, it moved to new continents and farmlands causing misery and despair. But we haven’t given up. Plant pathologists are hard at work learning more about these parasites and applying new knowledge and technologies to build disease-resistant crops.


Via Kamoun Lab @ TSL
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Interview with Jeffrey L. Dangl

Interview with Jeffrey L. Dangl | Plant immunity | Scoop.it

Jeff Dangl was born in Grand Rapids, Michigan, USA. His family moved to Redding, in the beautiful north of California, when Jeff was aged 5. He grew up fishing in the lakes and streams of the great North State and hunting ducks and geese on the Pacific Flyway. This introduction to field biology spurred Jeff's interest, and he studied Biological Sciences and English, with a specialization in Modern Literature, at Stanford University as an undergraduate, earning dual Bachelor's degrees in 1981. Jeff had the good fortune to find a summer job in 1978, learning how to run and manage the fluorescence-activated cell sorter (FACS) in the lab of its creator, Prof. Leonard A. Herzenberg, in the Genetics Department at Stanford University School of Medicine. That experience led to an 8 year stint in the Herzenberg lab as an undergraduate, a gap-year research student, and finally as a doctoral student. Jeff created some of the world's first human–mouse chimeric immunoglobulins using the then new recombinant DNA techniques. He switched gears to plant defense responses as an National Science Foundation (NSF) Plant Molecular Biology postdoctoral fellow in Klaus Hahlbrock's department at the Max Planck Institute for Plant Breeding in Cologne, Germany. Jeff lucked into another job, as a Group Leader at the Max Delbrück Laboratory in Cologne, where he was given free rein to apply the emerging model Arabidopsis to problems in plant pathology. Jeff moved to the University of North Carolina (UNC) in 1995 and became a Howard Hughes–Gordon and Betty Moore Plant Science Investigator in 2011. Jeff's research has been recognized by several awards, including elections to the US National Academy of Sciences and the German National Academy (Die Leopoldina). His group's research interests include mechanisms of plant Nod-like receptor (NLR) activation, understanding how pathogen effectors manipulate host cellular machinery, and trying to define rules to assemble synthetic microbial rhizosphere communities that can enhance plant performance.
What influenced your path into plant biology?

At graduate school my then girlfriend, Sarah Grant (now my wife and a Professor here at UNC) told me that if I had any intention of continuing our relationship I would need to find a postdoctoral post in Cologne, because that was where she was going after finishing her PhD at Stanford in Stan Cohen's lab. Not being thoroughly stupid, I did as I was told.
How did you decide on your current research topics?

I stumbled upon a paper in Proc. Natl. Acad. Sci. USA from the lab of Klaus Hahlbrock, who was then still in Freiburg, describing transcriptional activation of ‘plant defense genes’. I had never considered that plants could recognize pathogens, let alone do so with exquisite specificity. I did a lot of reading. The genetics of disease resistance, elegantly presented by H.H. Flor, Al Ellingboe, Tony Pryor, and Noel Keen, really convinced me that plants must have an immune system based on receptors dedicated to recognizing pathogens. It seemed like terra incognita and I was hooked.
What would you be if you were not a plant biologist?

An architect.
Do you have a scientific hero?

Len Herzenberg, Jeff Schell, Chris Somerville.
What paper influenced you most?

The original papers from Susumu Tonegawa, Lee Hood, and others describing the discovery of somatic DNA rearrangements in immunoglobulin genes were a stunning tour de force. This early work, first published in Proc. Natl. Acad. Sci. in 1976, is reviewed in S. Tonegawa (1983) ‘Somatic generation of antibody diversity’, Nature 302, 575–581. Every week or month there was a new breakthrough. I have never been associated with such a frenzied field since. There's a great summary of this fantastically exciting time in molecular genetics at: http://www.nature.com/ni/focus/chromatin_dynamics/classics/vdj.html.
What is the best advice you have been given?

The best advice I ever received was from Len Herzenberg, but it was not delivered as advice, but rather as a life force – enjoy science, always keep your eyes open to the wonder of discovery, and stay focused on the science. Len was remarkably able to ignore the tedious trivia of lab management and departmental soap opera.
What advice would you give?

Be your own toughest critic and do not be afraid to kill your own dogma ...


Via Christophe Jacquet
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Plant PRRs and the Activation of Innate Immune Signaling: Molecular Cell

Plant PRRs and the Activation of Innate Immune Signaling: Molecular Cell | Plant immunity | Scoop.it

Despite being sessile organisms constantly exposed to potential pathogens and pests, plants are surprisingly resilient to infections. Plants can detect invaders via the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs). Plant PRRs are surface-localized receptor-like kinases, which comprise a ligand-binding ectodomain and an intracellular kinase domain, or receptor-like proteins, which do not exhibit any known intracellular signaling domain. In this review, we summarize recent discoveries that shed light on the molecular mechanisms underlying ligand perception and subsequent activation of plant PRRs. Notably, plant PRRs appear as central components of multiprotein complexes at the plasma membrane that contain additional transmembrane and cytosolic kinases required for the initiation and specificity of immune signaling. PRR complexes are under tight control by protein phosphatases, E3 ligases, and other regulatory proteins, illustrating the exquisite and complex regulation of these molecular machines whose proper activation underlines a crucial layer of plant immunity.


Via IPM Lab, CP
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PLOS Pathogens: Functionally Redundant RXLR Effectors from Phytophthora infestans Act at Different Steps to Suppress Early flg22-Triggered Immunity (2014)

PLOS Pathogens: Functionally Redundant RXLR Effectors from Phytophthora infestans Act at Different Steps to Suppress Early flg22-Triggered Immunity (2014) | Plant immunity | Scoop.it

Genome sequences of several economically important phytopathogenic oomycetes have revealed the presence of large families of so-called RXLR effectors. Functional screens have identified RXLR effector repertoires that either compromise or induce plant defense responses. However, limited information is available about the molecular mechanisms underlying the modes of action of these effectors in planta. The perception of highly conserved pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs), such as flg22, triggers converging signaling pathways recruiting MAP kinase cascades and inducing transcriptional re-programming, yielding a generic anti-microbial response. We used a highly synchronizable, pathogen-free protoplast-based assay to identify a set of RXLR effectors from Phytophthora infestans (PiRXLRs), the causal agent of potato and tomato light blight that manipulate early stages of flg22-triggered signaling. Of thirty-three tested PiRXLR effector candidates, eight, called Suppressor of early Flg22-induced Immune response (SFI), significantly suppressed flg22-dependent activation of a reporter gene under control of a typical MAMP-inducible promoter (pFRK1-Luc) in tomato protoplasts. We extended our analysis to Arabidopsis thaliana, a non-host plant species of P. infestans. From the aforementioned eight SFI effectors, three appeared to share similar functions in both Arabidopsis and tomato by suppressing transcriptional activation of flg22-induced marker genes downstream of post-translational MAP kinase activation. A further three effectors interfere with MAMP signaling at, or upstream of, the MAP kinase cascade in tomato, but not in Arabidopsis. Transient expression of the SFI effectors in Nicotiana benthamianaenhances susceptibility to P. infestans and, for the most potent effector, SFI1, nuclear localization is required for both suppression of MAMP signaling and virulence function. The present study provides a framework to decipher the molecular mechanisms underlying the manipulation of host MAMP-triggered immunity (MTI) by P. infestans and to understand the basis of host versus non-host resistance in plants towards P. infestans.


Via Kamoun Lab @ TSL, CP
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RiceWiki: a wiki-based database for community curation of rice genes

RiceWiki: a wiki-based database for community curation of rice genes | Plant immunity | Scoop.it

Via Elsa Ballini
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MPMI: Pseudomonas syringae evades host immunity by degrading flagellin monomers with alkaline protease AprA (2014)

MPMI: Pseudomonas syringae evades host immunity by degrading flagellin monomers with alkaline protease AprA (2014) | Plant immunity | Scoop.it

Bacterial flagellin molecules are strong inducers of innate immune responses in both mammals and plants. The opportunistic pathogenPseudomonas aeruginosa secretes an alkaline protease called AprA that degrades flagellin monomers. Here, we show that AprA is widespread among a wide variety of bacterial species. In addition we investigated the role of AprA in virulence of the bacterial plant pathogen Pseudomonas syringae pv. tomato DC3000 (Pst). The AprA-deficient Pst ∆aprA knockout mutant was significantly less virulent on both tomato and A. thaliana. Moreover, infiltration of A. thaliana Col-0 leaves with Pst ∆aprA evoked a significantly higher level of expression of the defense-related genes FRK1 and PR-1 than did wild-type Pst. In the flagellin receptor mutant fls2, pathogen virulence and defense-related gene activation did not differ between Pst and Pst ∆aprA. Together, these results suggest that AprA of Pst is important for evasion of recognition by the FLS2 receptor, allowing wild-type Pst to be more virulent on its host plant than AprA-deficient Pst ∆aprA. To provide further evidence for the role of Pst AprA in host immune evasion, we overexpressed the AprA inhibitory peptide AprI of Pst in A. thaliana to counteract the immune evasive capacity of Pst AprA. Ectopic expression of aprI in A. thaliana resulted in an enhanced level of resistance against wild-type Pst, while the already elevated level of resistance against Pst ∆aprA remained unchanged. Together, these results indicate that evasion of host immunity by the alkaline protease AprA is important for full virulence of Pst and likely acts by preventing flagellin monomers from being recognized by its cognate immune receptor.


Via Kamoun Lab @ TSL, Suayib Üstün, Christophe Jacquet
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Paleo-evolutionary plasticity of plant disease resistance genes

Paleo-evolutionary plasticity of plant disease resistance genes | Plant immunity | Scoop.it
The recent access to a large set of genome sequences, combined with a robust evolutionary scenario of modern monocot (i.e. grasses) and eudicot (i.e. rosids) species from their founder ancestors, offered the opportunity to gain insights into disease resistance genes (R-genes) evolutionary plasticity.

Via Elsa Ballini
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