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PLOS Pathogens: Transcription Factor Amr1 Induces Melanin Biosynthesis and Suppresses Virulence in Alternaria brassicicola

PLOS Pathogens: Transcription Factor Amr1 Induces Melanin Biosynthesis and Suppresses Virulence in Alternaria brassicicola | Plant-Microbe Interaction | Scoop.it

Induction of cell wall-degrading enzymes, secretion of toxins, enforcement of fungal cell wall architecture, and detoxification of host defense molecules are important or essential for the fungal infection of plants. Genes important for each of these functions have been identified in various fungal species. Understanding how these genes are coordinately regulated and how many regulators are involved in the process is a challenge. We recently discovered a transcription factor gene, AbVf19, which positively regulates hydrolytic enzyme-coding genes. Here, we report on another transcription factor gene, Amr1, which negatively regulates a subset of these genes during late-stage pathogenesis and positively regulates melanin biosynthesis during conidiogenesis. This study adds another dimension to the complex regulation and overall importance of hydrolytic enzyme genes during plant pathogenesis by necrotrophic fungi. In addition, this study provides an example on the evolutionary implication of virulence in the necrotrophic fungus, A. brassicicola. One transcription factor essential for long-term survival because of its role in melanin biosynthesis is used instead to suppress virulence. We speculate that the suppressive functions of Amr1 contribute to the specialized adaptation of A. brassicicola as an efficient and successful facultative parasite.

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Characteristics and safety assessment of intractable proteins in genetically modified crops

Characteristics and safety assessment of intractable proteins in genetically modified crops | Plant-Microbe Interaction | Scoop.it

“Intractable proteins” in GM crops cannot be isolated or studied by existing methods.

Intractability results from low expression, membrane association, or other factors.

The established tiered weight-of-evidence approach can be used for safety assessment.

No protein is needed for history of safe use (HOSU) and bioinformatics analyses.

Enriched or substitute proteins may offer alternatives to pure protein dose testing.


Via Elsa Ballini
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Chimaeric viruses blur the borders between the major groups of eukaryotic ssDNA viruses

Chimaeric viruses blur the borders between the major groups of eukaryotic ssDNA viruses | Plant-Microbe Interaction | Scoop.it

Metagenomic studies have uncovered an astonishing diversity of ssDNA viruses encoding replication proteins (Reps) related to those of eukaryotic Circoviridae, Geminiviridae orNanoviridae; however, exact evolutionary relationships among these viruses remain obscure. Recently, a unique chimeric virus (CHIV) genome, which has apparently emerged via recombination between ssRNA and ssDNA viruses, has been discovered. Here we report on the assembly of 13 new CHIV genomes recovered from various environments. Our results indicate a single event of capsid protein (CP) gene capture from an RNA virus in the history of this virus group. The domestication of the CP gene was followed by an unprecedented recurrent replacement of the Rep genes in CHIVs with distant counterparts from diverse ssDNA viruses. We suggest that parasitic and symbiotic interactions between unicellular eukaryotes were central for the emergence of CHIVs and that such turbulent evolution was primarily dictated by incongruence between the CP and Rep proteins.

  


Via Ed Rybicki
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Ed Rybicki's curator insight, June 30, 4:41 AM

...and we are about to look for some of these in a big way in seawater

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The Arabidopsis LecRK-VI.2 associates with the pattern-recognition receptor FLS2 and primes Nicotiana benthamiana pattern-triggered immunity - Huang - 2014 - The Plant Journal - Wiley Online Library

The Arabidopsis LecRK-VI.2 associates with the pattern-recognition receptor FLS2 and primes Nicotiana benthamiana pattern-triggered immunity - Huang - 2014 - The Plant Journal - Wiley Online Library | Plant-Microbe Interaction | Scoop.it

Pattern-triggered immunity (PTI) is broad spectrum and manipulation of PTI is believed to represent an attractive way to engineer plants with broad-spectrum disease resistance. PTI is activated upon perception of microbe-associated molecular patterns (MAMPs) by pattern-recognition receptors (PRRs). We have recently demonstrated that the L-type lectin receptor kinase-VI.2 (LecRK-VI.2) positively regulates Arabidopsis thaliana PTI. Here we show through in vitro pull-down, bimolecular fluorescence complementation and co-immunoprecipitation analyses that LecRK-VI.2 associates with the PRR FLS2. We also demonstrated that LecRK-VI.2 from the cruciferous plant Arabidopsis remains functional after interfamily transfer to the Solanaceous plant Nicotiana benthamiana. Wild tobacco plants ectopically expressing LecRK-VI.2 were indeed more resistant to virulent hemi-biotrophic and necrotrophic bacteria, but not to the fungal pathogen Botrytis cinerea suggesting that, as with Arabidopsis, the LecRK-VI.2 protective effect in N. benthamiana is bacteria specific. Ectopic expression of LecRK-VI.2 in N. benthamiana primed PTI-mediated reactive oxygen species production, mitogen-activated protein kinase (MAPK) activity, callose deposition and gene expression upon treatment with the MAMP flagellin. Our findings identified LecRK-VI.2 as a member of the FLS2 receptor complex and suggest that heterologous expression of components of PRR complexes can be used as tools to engineer plant disease resistance to bacteria.


Via Suayib Üstün
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New Phytol.: Engaging students with plant science: the Plant Science TREE (2014)

New Phytol.: Engaging students with plant science: the Plant Science TREE (2014) | Plant-Microbe Interaction | Scoop.it

In this paper, we show how a single web resource can engage a wide student audience with plant science. Developed by the University of Leeds, UK, the Plant Science TREE (Tool for Research Engaged Education (www.tree.leeds.ac.uk)) is an online teaching tool giving access to online research lectures, downloadable lecture slides, practicals, movies and other material on topical plant science to support lecturers in their teaching. The Plant Science TREE complements the annual Gatsby Plant Science Summer School, which has already succeeded in engaging undergraduates with plant science (Levesley et al., 2012). Both initiatives were instigated to address the decline in student numbers in plant science (Sundberg, 2004; Stagg et al., 2009; Jones, 2010; Drea, 2011) at a time when there is concern that future demand for plant scientists will not be met (The Royal Society, 2009). The causes of this decline are unproven but may be the result of a combination of factors including, greater preference by students for animal and medically-based degrees, disengagement from plant science at school, and narrowing of plant-based undergraduate curricula. Where the summer school aims, by face-to-face contact, to inspire relatively small numbers of high-achieving students to consider plant science as a career option, the Plant Science TREE aims to reach a much larger, more diverse global audience through the use of web technologies.

 

Aurora Levesley, Steve Paxton, Richard Collins, Alison Baker and Celia Knight


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The bacterial lipopeptide iturins induce Verticillium dahliae cell death by affecting fungal signaling pathways and mediate plant defense responses involved in PAMP-triggered immunity

The bacterial lipopeptide iturins induce Verticillium dahliae cell death by affecting fungal signaling pathways and mediate plant defense responses involved in PAMP-triggered immunity | Plant-Microbe Interaction | Scoop.it

Verticillium wilt in cotton caused by Verticillium dahliae is one of the most serious plant diseases worldwide. Because no known fungicides or cotton cultivars provide sufficient protection against this pathogen, V. dahliae causes major crop yield losses. Here, an isolated cotton endophytic bacterium, designated Bacillus amyloliquefaciens 41B-1, exhibited greater than 50% biocontrol efficacy against V. dahliae in cotton plants under greenhouse conditions. Through HPLC and mass analysis of the filtrate, we found that the antifungal compounds present in the strain 41B-1 culture filtrate were a series of isoforms of iturins. The purified iturins suppressed V. dahliae microsclerotial germination in the absence or presence of cotton. Treatment with the iturins induced ROS bursts, Hog1 MAPK activation and defects in cell wall integrity. The oxidative stress response and high-osmolarity glycerol pathway contribute to iturins resistance in V. dahliae. In contrast, the Slt2 MAPK pathway may be involved in iturins sensitivity in this fungus. In addition to antagonism, iturins could induce plant defense responses as activators and mediate PAMP-triggered immunity. These findings suggest that iturins may affect fungal signaling pathways and mediate plant defense responses against V. dahliae.


Via Christophe Jacquet
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Atlas of nonribosomal peptide and polyketide biosynthetic pathways reveals common occurrence of nonmodular enzymes

Atlas of nonribosomal peptide and polyketide biosynthetic pathways reveals common occurrence of nonmodular enzymes | Plant-Microbe Interaction | Scoop.it
Nonribosomal peptides and polyketides are a diverse group of natural products with complex chemical structures and enormous pharmaceutical potential. They are synthesized on modular nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) enzyme complexes by a conserved thiotemplate mechanism. Here, we report the widespread occurrence of NRPS and PKS genetic machinery across the three domains of life with the discovery of 3,339 gene clusters from 991 organisms, by examining a total of 2,699 genomes. These gene clusters display extraordinarily diverse organizations, and a total of 1,147 hybrid NRPS/PKS clusters were found. Surprisingly, 10% of bacterial gene clusters lacked modular organization, and instead catalytic domains were mostly encoded as separate proteins. The finding of common occurrence of nonmodular NRPS differs substantially from the current classification. Sequence analysis indicates that the evolution of NRPS machineries was driven by a combination of common descent and horizontal gene transfer. We identified related siderophore NRPS gene clusters that encoded modular and nonmodular NRPS enzymes organized in a gradient. A higher frequency of the NRPS and PKS gene clusters was detected from bacteria compared with archaea or eukarya. They commonly occurred in the phyla of Proteobacteria, Actinobacteria, Firmicutes, and Cyanobacteria in bacteria and the phylum of Ascomycota in fungi. The majority of these NRPS and PKS gene clusters have unknown end products highlighting the power of genome mining in identifying novel genetic machinery for the biosynthesis of secondary metabolites.
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Natural loss-of-function mutation of EDR1 conferring resistance to tomato powdery mildew in Arabidopsis thaliana accession C24

Natural loss-of-function mutation of EDR1 conferring resistance to tomato powdery mildew in Arabidopsis thaliana accession C24 | Plant-Microbe Interaction | Scoop.it

To screen for potentially novel types of resistance to tomato powdery mildew Oidium neolycopersici, a disease assay was performed on 123 Arabidopsis thaliana accessions. Forty accessions were fully resistant, and one of them, C24, was analysed in detail. By quantitative trait locus (QTL) analysis of an F2 population derived from C24 X Sha (susceptible accession), two QTL associated with resistance were identified in C24. Fine-mapping of QTL-1 on chromosome 1 delimited the region to an interval of 58 kb encompassing 15 candidate genes. One of these was Enhanced Disease Resistance 1 (EDR1). Evaluation of the previously obtained edr1 mutant of Arabidopsis accession Col-0, which was identified because of its resistance to powdery mildew G. cichoracearum, showed that it also displayed resistance to O. neolycopersici. Sequencing of EDR1 in our C24 germplasm (referred to as C24-W) revealed two missing nucleotides in the second exon of EDR1 resulting in a premature stop codon. Remarkably, C24 obtained from other laboratories do not contain the EDR1 mutation. To verify the identity of C24-W, a DNA region containing a SNP unique to C24 was sequenced showing that C24-W contains the C24-specific nucleotide. C24-W showed enhanced resistance to O. neolycopersici compared with the C24 not containing edr1 mutation. Furthermore, C24-W displayed a dwarf phenotype, which was not associated with the mutation in EDR1 nor caused by differential accumulation of pathogenesis-related genes. In conclusion we identified a natural edr1 mutant in the background of C24.

 

 


Via Christophe Jacquet
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Curr. Op. Plant Biol.: Special issue on biotic interactions (2014)

From local to global: CDPKs in systemic defense signaling upon microbial and herbivore attack

    Tina Romeis, Marco Herde

 

Actinorhizal root nodule symbioses: what is signalling telling on the origins of nodulation?

    Sergio Svistoonoff, Valérie Hocher, Hassen Gherbi

 

Inside plant: biotrophic strategies to modulate host immunity and metabolism

    Bilal Ökmen, Gunther Doehlemann

 

Phytohormone signaling in arbuscular mycorhiza development

    Caroline Gutjahr

 

Transcriptional control of plant defence responses

    Pierre Buscaill, Susana Rivas

 

Immune receptor complexes at the plant cell surface

    Hannah Böhm, Isabell Albert, Li Fan, André Reinhard, Thorsten Nürnberger

 

Structural insight into the activation of plant receptor kinases

    Zhifu Han, Yadong Sun, Jijie Chai

 

Perception of the plant immune signal salicylic acid

    Shunping Yan, Xinnian Dong

 

The changing of the guard: the Pto/Prf receptor complex of tomato and pathogen recognition

    Vardis Ntoukakis, Isabel ML Saur, Brendon Conlan, John P Rathjen

 

Microbe–microbe interactions determine oomycete and fungal host colonization

    Eric Kemen

 

Extracellular ATP is a central signaling molecule in plant stress responses

    Yangrong Cao, Kiwamu Tanaka, Cuong T Nguyen, Gary Stacey

 

Interaction between viral RNA silencing suppressors and host factors in plant immunity

    Kenji S Nakahara, Chikara Masuta

 

Filamentous pathogen effector functions: of pathogens, hosts and microbiomes

    Hanna Rovenich, Jordi C Boshoven, Bart PHJ Thomma

 

Staying in touch: mechanical signals in plant–microbe interactions

    Dhileepkumar Jayaraman, Simon Gilroy, Jean-Michel Ané

 

Opening the Ralstonia solanacearum type III effector tool box: insights into host cell subversion mechanisms

    Laurent Deslandes, Stephane Genin

 

Cross-interference of plant development and plant–microbe interactions

    Edouard Evangelisti, Thomas Rey, Sebastian Schornack


Via Nicolas Denancé
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Cross-interference of plant development and plant–microbe interactions

Cross-interference of plant development and plant–microbe interactions | Plant-Microbe Interaction | Scoop.it

Plant roots are host to a multitude of filamentous microorganisms. Among these, arbuscular mycorrhizal fungi provide benefits to plants, while pathogens trigger diseases resulting in significant crop yield losses. It is therefore imperative to study processes which allow plants to discriminate detrimental and beneficial interactions in order to protect crops from diseases while retaining the ability for sustainable bio-fertilisation strategies. Accumulating evidence suggests that some symbiosis processes also affect plant–pathogen interactions. A large part of this overlap likely constitutes plant developmental processes. Moreover, microbes utilise effector proteins to interfere with plant development. Here we list relevant recent findings on how plant–microbe interactions intersect with plant development and highlight future research leads.


Via Christophe Jacquet
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Rescooped by Guogen Yang from Fungal|Oomycete Biology
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Speciation in Fungal and Oomycete Plant Pathogens

Speciation in Fungal and Oomycete Plant Pathogens | Plant-Microbe Interaction | Scoop.it

The process of speciation, by definition, involves evolution of one or more reproductive isolating mechanisms that split a single species into two that can no longer interbreed. Determination of which processes are responsible for speciation is important yet challenging. Several studies have proposed that speciation in pathogens is heavily influenced by host-pathogen dynamics and that traits that mediate such interactions (e.g., host mobility, reproductive mode of the pathogen, complexity of the life cycle, and host specificity) must lead to reproductive isolation and ultimately affect speciation rates. In this review, we summarize the main evolutionary processes that lead to speciation of fungal and oomycete plant pathogens and provide an outline of how speciation can be studied rigorously, including novel genetic/genomic developments.


Via Alejandro Rojas
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The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes

The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes | Plant-Microbe Interaction | Scoop.it

Phytophthora infestans is a destructive plant pathogen best known for causing the disease that triggered the Irish potato famine and remains the most costly potato pathogen to manage worldwide. Identification of P. infestan’s elusive center of origin is critical to understanding the mechanisms of repeated global emergence of this pathogen. There are two competing theories, placing the origin in either South America or in central Mexico, both of which are centers of diversity of Solanum host plants. To test these competing hypotheses, we conducted detailed phylogeographic and approximate Bayesian computation analyses, which are suitable approaches to unraveling complex demographic histories. Our analyses used microsatellite markers and sequences of four nuclear genes sampled from populations in the Andes, Mexico, and elsewhere. To infer the ancestral state, we included the closest known relatives Phytophthora phaseoli, Phytophthora mirabilis, and Phytophthora ipomoeae, as well as the interspecific hybrid Phytophthora andina. We did not find support for an Andean origin of P. infestans; rather, the sequence data suggest a Mexican origin. Our findings support the hypothesis that populations found in the Andes are descendants of the Mexican populations and reconcile previous findings of ancestral variation in the Andes. Although centers of origin are well documented as centers of evolution and diversity for numerous crop plants, the number of plant pathogens with a known geographic origin are limited. This work has important implications for our understanding of the coevolution of hosts and pathogens, as well as the harnessing of plant disease resistance to manage late blight.

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Overexpression of Phosphomimic Mutated OsWRKY53 Leads to Enhanced Blast Resistance in Rice

Overexpression of Phosphomimic Mutated OsWRKY53 Leads to Enhanced Blast Resistance in Rice | Plant-Microbe Interaction | Scoop.it

We previously reported that OsWRKY53-overexpressing rice plants showed enhanced resistance to the rice blast fungus. In this study, we identified OsWRKY53 as a substrate of OsMPK3/OsMPK6, components of a fungal PAMP-responsive MAPK cascade in rice, and analyzed the effect of OsWRKY53 phosphorylation on the regulation of basal defense responses to Magnaporthe oryzae .


Via Elsa Ballini
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Functional diversity of five homologous Cu+-ATPases present in Sinorhizobium meliloti

Copper is an important element in host–microbe interactions, acting both as a catalyst in enzymes and as a potential toxin. Cu+-ATPases drive cytoplasmic Cu+ efflux and protect bacteria against metal overload. Many pathogenic and symbiotic bacteria contain multiple Cu+-ATPase genes within particular genetic environments, suggesting alternative roles for each resulting protein. This hypothesis was tested by characterizing five homologous Cu+-ATPases present in the symbiotic organism Sinorhizobium meliloti. Mutation of each gene led to different phenotypes and abnormal nodule development in the alfalfa host. Distinct responses were detected in free-living S. meliloti mutant strains exposed to metal and redox stresses. Differential gene expression was detected under Cu+, oxygen or nitrosative stress. These observations suggest that CopA1a maintains the cytoplasmic Cu+ quota and its expression is controlled by Cu+ levels. CopA1b is also regulated by Cu+ concentrations and is required during symbiosis for bacteroid maturation. CopA2-like proteins, FixI1 and FixI2, are necessary for the assembly of two different cytochrome c oxidases at different stages of bacterial life. CopA3 is a phylogenetically distinct Cu+-ATPase that does not contribute to Cu+ tolerance. It is regulated by redox stress and required during symbiosis. We postulated a model where non-redundant homologous Cu+-ATPases, operating under distinct regulation, transport Cu+ to different target proteins.


Via Jean-Michel Ané
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Fungi borrowed bacterial gene again and again

Fungi borrowed bacterial gene again and again | Plant-Microbe Interaction | Scoop.it
Multiple independent gene transfers gave fungi ability to colonize plant roots.

Muller and his colleagues scanned the genomes of 149 eukaryotes, and found acdS-like genes in 65 of them — 61 in fungi and 4 in parasitic microorganisms called oomycetes, including Phytophthora infestans, the microbe responsible for the Irish potato famine. After analysing the organisms' genetic family trees, the researchers determined that the most likely explanation was that three different kinds of bacterium had donated the gene to the fungi and oomycetes in a total of 15 different horizontal-gene-transfer events.


Via Francis Martin
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A field guide to whole-genome sequencing, assembly and annotation

A field guide to whole-genome sequencing, assembly and annotation | Plant-Microbe Interaction | Scoop.it

Genome sequencing projects were long confined to biomedical model organisms and required the concerted effort of large consortia. Rapid progress in high-throughput sequencing technology and the simultaneous development of bioinformatic tools have democratized the field. It is now within reach for individual research groups in the eco-evolutionary and conservation community to generate de novo draft genome sequences for any organism of choice. Because of the cost and considerable effort involved in such an endeavour, the important first step is to thoroughly consider whether a genome sequence is necessary for addressing the biological question at hand. Once this decision is taken, a genome project requires careful planning with respect to the organism involved and the intended quality of the genome draft. Here, we briefly review the state of the art within this field and provide a step-by-step introduction to the workflow involved in genome sequencing, assembly and annotation with particular reference to large and complex genomes. This tutorial is targeted at scientists with a background in conservation genetics, but more generally, provides useful practical guidance for researchers engaging in whole-genome sequencing projects.


Via Francis Martin
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Rescooped by Guogen Yang from Plants&Bacteria
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Elucidation of a pH-folding switch in the Pseudomonas syringae effector protein AvrPto

Elucidation of a pH-folding switch in the Pseudomonas syringae effector protein AvrPto | Plant-Microbe Interaction | Scoop.it

Scooped from: PNAS, 2009.

Authors: Jennifer E. Dawson, Jolita Šečkutė, Soumya De, Samuel A. Schueler, Aaron B. Oswald and Linda K. Nicholson.

 

Abstract:

Pathogenic bacteria have developed extraordinary strategies for invading host cells. The highly conserved type III secretion system (T3SS) provides a regulated conduit between the bacterial and host cytoplasm for delivery of a specific set of bacterial effector proteins that serve to disrupt host signaling and metabolism for the benefit of the bacterium. Remarkably, the inner diameter of the T3SS apparatus requires that effector proteins pass through in at least a partially unfolded form. AvrPto, an effector protein of the plant pathogen Pseudomonas syringae, adopts a helical bundle fold of low stability (ΔGF→U = 2 kcal/mol at pH 7, 26.6 °C) and offers a model system for chaperone-independent secretion. P. syringae effector proteins encounter a pH gradient as they translocate from the bacterial cytoplasm (mildly acidic) into the host cell (neutral). Here, we demonstrate that AvrPto possesses a pH-sensitive folding switch controlled by conserved residue H87 that operates precisely in the pH range expected between the bacterial and host cytoplasm environments. These results provide a mechanism for how a bacterial effector protein employs an intrinsic pH sensor to unfold for translocation via the T3SS and refold once in the host cytoplasm and provide fundamental insights for developing strategies for delivery of engineered therapeutic proteins to target tissues.


 


Via Freddy Monteiro
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Lipochitooligosaccharide recognition: an ancient story

Lipochitooligosaccharide recognition: an ancient story | Plant-Microbe Interaction | Scoop.it

Chitin is the second most abundant polysaccharide in nature, found in crustacean shells, insect exoskeletons and fungal cell walls. The action of chitin and chitin derivatives on plants has become a very interesting story of late. Chitin is a β1-4-linked polymer of N-acetyl-d-glucosamine (GlcNAc). In this unmodified form, chitooligosaccharides (degree of polymerization (dp) = 6–8)) are strong inducers of plant innate immunity. By contrast, when these chitooligosaccharides are acylated (so-called lipochitooligosaccharides, LCOs) and further modified, they can act as Nod factors, the key signaling molecules that play an important role in the initiation of the legume–rhizobium symbiosis. In a similar form, these molecules can also act as Myc factors, the key signaling molecules involved in the arbuscular mycorrhizal (AM) symbiosis. It has been proposed that Nod factor perception might have evolved from the more ancient AM symbiosis. Increasing evidence now suggests that LCO perception might have evolved from plant innate immunity signaling. In this review, we will discuss the evolutionary origin of symbiotic LCO recognition.


Via Francis Martin
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Plant & Cell Physiol: Ectopic Expression of RESISTANCE TO POWDERY MILDEW8.1 Confers Resistance to Fungal and Oomycete Pathogens in Arabidopsis (2014)

Plant & Cell Physiol: Ectopic Expression of RESISTANCE TO POWDERY MILDEW8.1 Confers Resistance to Fungal and Oomycete Pathogens in Arabidopsis (2014) | Plant-Microbe Interaction | Scoop.it

Broad-spectrum disease resistance is a highly valuable trait in plant breeding and attracts special attention in research. The Arabidopsis gene locus RESISTANCE TO POWDERY MILDEW 8 (RPW8) contains two adjacent homologous genes, RPW8.1 and RPW8.2, and confers broad-spectrum resistance to powdery mildew. Remarkably, the RPW8.2 protein is specifically localized to the extrahaustorial membrane (EHM) encasing the feeding structure of powdery mildew whereby RPW8.2 activates haustorium-targeted defenses. Here, we show that ectopic expression of the yellow fluorescent protein (YFP)-tagged RPW8.1 from the native promoter leads to unique cell death lesions and enhances resistance to virulent fungal and oomycete pathogens that cause powdery mildew and downy mildew diseases, respectively. In powdery mildew infected plants, RPW8.1-YFP accumulates at higher levels in the mesophyll cells underneath the infected epidermal cells where RPW8.2-YFP is mainly expressed. This cell-type-preferential protein accumulation pattern largely correlates with that of H2O2 accumulation, suggesting that RPW8.1 may spatially collaborate with RPW8.2 in activation of resistance to powdery mildew. Interestingly, when ectopically expressed from theRPW8.2 promoter, RPW8.1-YFP is also targeted to the EHM of powdery mildew and the transgenic plants display resistance to both powdery mildew and downy mildew. Using YFP as a reporter, we further reveal that the RPW8.1 promoter is constitutively active but induced to higher levels in cells at the infection site, whereas the RPW8.2 promoter is activated specifically in cells at the infection site. Taken together, our results suggest that RPW8.1 (and its promoter) is functionally distinct fromRPW8.2 and may have a higher potential in engineering broad-spectrum resistance in plants.


Via Kamoun Lab @ TSL
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PLOS One: Mutational Analysis of the Ve1 Immune Receptor That Mediates Verticillium Resistance in Tomato (2014)

PLOS One: Mutational Analysis of the Ve1 Immune Receptor That Mediates Verticillium Resistance in Tomato (2014) | Plant-Microbe Interaction | Scoop.it

Pathogenic Verticillium species are economically important plant pathogens that cause vascular wilt diseases in hundreds of plant species. The Ve1 gene of tomato confers resistance against race 1 strains of Verticillium dahliae and V. albo-atrum. Ve1 encodes an extracellular leucine-rich repeat (eLRR) receptor-like protein (RLP) that serves as a cell surface receptor for recognition of the recently identified secreted Verticillium effector Ave1. To investigate recognition of Ave1 by Ve1, alanine scanning was performed on the solvent exposed β-strand/β-turn residues across the eLRR domain of Ve1. In addition, alanine scanning was also employed to functionally characterize motifs that putatively mediate protein-protein interactions and endocytosis in the transmembrane domain and the cytoplasmic tail of the Ve1 protein. Functionality of the mutant proteins was assessed by screening for the occurrence of a hypersensitive response upon co-expression with Ave1 upon Agrobacterium tumefaciens-mediated transient expression (agroinfiltration). In order to confirm the agroinfiltration results, constructs encoding Ve1 mutants were transformed into Arabidopsis and the transgenes were challenged with race 1 Verticillium. Our analyses identified several regions of the Ve1 protein that are required for functionality.


Via Kamoun Lab @ TSL
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Plant Cell (review): Intervention of Phytohormone Pathways by Pathogen Effectors

Plant Cell (review): Intervention of Phytohormone Pathways by Pathogen Effectors | Plant-Microbe Interaction | Scoop.it

"The constant struggle between plants and microbes has driven the evolution of multiple defense strategies in the host as well as offense strategies in the pathogen. To defend themselves from pathogen attack, plants often rely on elaborate signaling networks regulated by phytohormones. In turn, pathogens have adopted innovative strategies to manipulate phytohormone-regulated defenses. "


Via Mary Williams
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The genome of Eucalyptus grandis : Nature

The genome of Eucalyptus grandis : Nature | Plant-Microbe Interaction | Scoop.it

Eucalypts are the world’s most widely planted hardwood trees. Their outstanding diversity, adaptability and growth have made them a global renewable resource of fibre and energy. We sequenced and assembled >94% of the 640-megabase genome of Eucalyptus grandis. Of 36,376 predicted protein-coding genes, 34% occur in tandem duplications, the largest proportion thus far in plant genomes. Eucalyptus also shows the highest diversity of genes for specialized metabolites such as terpenes that act as chemical defence and provide unique pharmaceutical oils. Genome sequencing of the E. grandis sister species E. globulus and a set of inbred E. grandis tree genomes reveals dynamic genome evolution and hotspots of inbreeding depression. The E. grandis genome is the first reference for the eudicot order Myrtales and is placed here sister to the eurosids. This resource expands our understanding of the unique biology of large woody perennials and provides a powerful tool to accelerate comparative biology, breeding and biotechnology.


Via Francis Martin
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A reference genome for common bean and genome-wide analysis of dual domestications : Nature Genetics : Nature Publishing Group

A reference genome for common bean and genome-wide analysis of dual domestications : Nature Genetics : Nature Publishing Group | Plant-Microbe Interaction | Scoop.it
Scott Jackson, Jeremy Schmutz, Phillip McClean and colleagues report the genome sequence of the common bean (Phaseolus vulgaris) and resequenced wild individuals and landraces from Mesoamerican and Andean gene pools, showing that common bean underwent two independent domestications.

Via Mary Williams
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Mary Williams's curator insight, June 10, 1:59 AM

Quite an intersting study on the origin of Phaseolus vulgaris based on genome sequences. You can see one of the lead authors talking about this work at this link

http://phys.org/news/2014-06-hill-beans-phaseolus-genome-insights.html

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A Novel Botrytis Species Is Associated with a Newly Emergent Foliar Disease in Cultivated Hemerocallis

A Novel Botrytis Species Is Associated with a Newly Emergent Foliar Disease in Cultivated Hemerocallis | Plant-Microbe Interaction | Scoop.it
Foliar tissue samples of cultivated daylilies (Hemerocallis hybrids) showing the symptoms of a newly emergent foliar disease known as ‘spring sickness’ were investigated for associated fungi. The cause(s) of this disease remain obscure. We isolated repeatedly a fungal species which proved to be member of the genus Botrytis, based on immunological tests. DNA sequence analysis of these isolates, using several different phyogenetically informative genes, indicated that they represent a new Botrytis species, most closely related to B. elliptica (lily blight, fire blight) which is a major pathogen of cultivated Lilium. The distinction of the isolates was confirmed by morphological analysis of asexual sporulating cultures. Pathogenicity tests on Hemerocallis tissues in vitro demonstrated that this new species was able to induce lesions and rapid tissue necrosis. Based on this data, we infer that this new species, described here as B. deweyae, is likely to be an important contributor to the development of ‘spring sickness’ symptoms. Pathogenesis may be promoted by developmental and environmental factors that favour assault by this necrotrophic pathogen. The emergence of this disease is suggested to have been triggered by breeding-related changes in cultivated hybrids, particularly the erosion of genetic diversity. Our investigation confirms that emergent plant diseases are important and deserve close monitoring, especially in intensively in-bred plants.
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Salicylic acid signaling inhibits apoplastic reactive oxygen species signaling

Salicylic acid signaling inhibits apoplastic reactive oxygen species signaling | Plant-Microbe Interaction | Scoop.it

Background

Reactive oxygen species (ROS) are used by plants as signaling molecules during stress and development. Given the amount of possible challenges a plant face from their environment, plants need to activate and prioritize between potentially conflicting defense signaling pathways. Until recently, most studies on signal interactions have focused on phytohormone interaction, such as the antagonistic relationship between salicylic acid (SA)-jasmonic acid and cytokinin-auxin.

Results

In this study, we report an antagonistic interaction between SA signaling and apoplastic ROS signaling. Treatment with ozone (O3) leads to a ROS burst in the apoplast and induces extensive changes in gene expression and elevation of defense hormones. However, Arabidopsis thaliana dnd1 (defense no death1) exhibited an attenuated response to O3. In addition, the dnd1 mutant displayed constitutive expression of defense genes and spontaneous cell death. To determine the exact process which blocks the apoplastic ROS signaling, double and triple mutants involved in various signaling pathway were generated in dnd1 background. Simultaneous elimination of SA-dependent and SA-independent signaling components from dnd1 restored its responsiveness to O3. Conversely, pre-treatment of plants with SA or using mutants that constitutively activate SA signaling led to an attenuation of changes in gene expression elicited by O3.

Conclusions

Based upon these findings, we conclude that plants are able to prioritize the response between ROS and SA via an antagonistic action of SA and SA signaling on apoplastic ROS signaling.

 

 


Via Christophe Jacquet
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Multiple recognition of RXLR effectors is associated with nonhost resistance of pepper against Phytophthora infestans

Multiple recognition of RXLR effectors is associated with nonhost resistance of pepper against Phytophthora infestans | Plant-Microbe Interaction | Scoop.it

Nonhost resistance (NHR) is a plant immune response to resist most pathogens. The molecular basis of NHR is poorly understood, but recognition of pathogen effectors by immune receptors, a response known as effector-triggered immunity, has been proposed as a component of NHR.We performed transient expression of 54 Phytophthora infestansRXLR effectors in pepper (Capsicum annuum) accessions. We used optimized heterologous expression methods and analyzed the inheritance of effector-induced cell death in an F2 population derived from a cross between two pepper accessions.Pepper showed a localized cell death response upon inoculation with P. infestans, suggesting that recognition of effectors may contribute to NHR in this system. Pepper accessions recognized as many as 36 effectors. Among the effectors, PexRD8 and Avrblb2 induced cell death in a broad range of pepper accessions. Segregation of effector-induced cell death in an F2 population derived from a cross between two pepper accessions fit 15 : 1, 9 : 7 or 3 : 1 ratios, depending on the effector.Our genetic data suggest that a single or two independent/complementary dominant genes are involved in the recognition of RXLR effectors. Multiple loci recognizing a series of effectors may underpin NHR of pepper to P. infestans and confer resistance durability.


Via Christophe Jacquet
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