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PLOS Pathogens: Ustilago maydis: Dissecting the Molecular Interface between Pathogen and Plant

PLOS Pathogens: Ustilago maydis: Dissecting the Molecular Interface between Pathogen and Plant | Plant-Microbe Interaction | Scoop.it
Fungal diseases of plants represent one of the most eminent threats to agriculture. Given the food needs of a growing world population and that more and more crops are devoted to fuel production, the necessity to develop crops with better resistance to disease is increasing. To accomplish this, the mechanisms that plant pathogenic fungi use to colonize plants need to be elucidated. As of now, there are only few examples/models in which this can be done on a functional, genome-wide level, taking into account both the pathogen and its host plant [1]. The fungus Ustilago maydis (U. maydis) is one of these examples. It is a member of the smut fungi: a large group of parasites infecting mostly grasses, including several important crop plants such as maize (Figure 1B), wheat, barley, and sugar cane. Smut fungi are biotrophs, i.e., parasites that need the living host plant to complete their sexual life cycle [2], [3]. They do not establish prominent feeding structures like the related, haustoria-forming rust fungi. During penetration, the host plasma membrane invaginates and completely encases the intracellular hyphae (Figure 1A), establishing an extended interaction zone [4] mediating the exchange of molecules between fungus and host. In contrast to most smut fungi that cause a systemic infection, remaining symptomless until the plant flowers, U. maydis can infect all above-ground parts of the maize plant but fails to spread systemically. U. maydis induces local tumors in which spores develop (Figure 1B) – a unique feature that allows detection of symptoms in corn seedlings less than a week after syringe infection with high levels of inoculum. This, together with the toolbox developed for reverse genetics, cell biology, and functional studies, has contributed to its status as a model for biotrophic basidiomycete fungi [5]. Here the current level of our understanding of the elaborate molecular crosstalk between U. maydis and its host plant will be discussed.

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Frontiers | Genome-wide transcriptional profiling of Botrytis cinerea genes targeting plant cell walls during infections of different hosts | Plant-Microbe Interaction

Cell walls are barriers that impair colonization of host tissues, but also are important reservoirs of energy-rich sugars. Growing hyphae of necrotrophic fungal pathogens, such as Botrytis cinerea (Botrytis, henceforth), secrete enzymes that disassemble cell wall polysaccharides. In this work we describe the annotation of 275 putative secreted Carbohydrate-Active enZymes (CAZymes) identified in the Botrytis B05.10 genome. Using RNAseq we determined which Botrytis CAZymes were expressed during infections of lettuce leaves, ripe tomato fruit, and grape berries. On the three hosts, Botrytis expressed a common group of 229 potentially secreted CAZymes, including 28 pectin backbone-modifying enzymes, 21 hemicellulose-modifying proteins, 18 enzymes that might target pectin and hemicellulose side-branches, and 16 enzymes predicted to degrade cellulose. The diversity of the Botrytis CAZymes may be partly responsible for its wide host range. Thirty-six candidate CAZymes with secretion signals were found exclusively when Botrytis interacted with ripe tomato fruit and grape berries. Pectin polysaccharides are notably abundant in grape and tomato cell walls, but lettuce leaf walls have less pectin and are richer in hemicelluloses and cellulose. The results of this study not only suggest that Botrytis targets similar wall polysaccharide networks on fruit and leaves, but also that it may selectively attack host wall polysaccharide substrates depending on the host tissue.

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Infographic: 9 plant diseases that threaten your favorite foods–and how GM can help | Genetic Literacy Project

Infographic: 9 plant diseases that threaten your favorite foods–and how GM can help | Genetic Literacy Project | Plant-Microbe Interaction | Scoop.it

"Nature is relentless, challenging farmers with weeds, insects and diseases. Advances in genetic modification offer some unique tools that can help increase food production despite these challenges."


Via Mary Williams
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Uniting the classification of cultured and uncultured bacteria and archaea using 16S rRNA gene sequences

Publicly available sequence databases of the small subunit ribosomal RNA gene, also known as 16S rRNA in bacteria and archaea, are growing rapidly, and the number of entries currently exceeds 4 million. However, a unified classification and nomenclature framework for all bacteria and archaea does not yet exist. In this Analysis article, we propose rational taxonomic boundaries for high taxa of bacteria and archaea on the basis of 16S rRNA gene sequence identities and suggest a rationale for the circumscription of uncultured taxa that is compatible with the taxonomy of cultured bacteria and archaea. Our analyses show that only nearly complete 16S rRNA sequences give accurate measures of taxonomic diversity. In addition, our analyses suggest that most of the 16S rRNA sequences of the high taxa will be discovered in environmental surveys by the end of the current decade.

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A Re-elicitation Assay to Correlate flg22-Signaling Competency with Ligand-Induced Endocytic Degradation of the FLS2 Receptor - Springer

A Re-elicitation Assay to Correlate flg22-Signaling Competency with Ligand-Induced Endocytic Degradation of the FLS2 Receptor - Springer | Plant-Microbe Interaction | Scoop.it

In the model plant Arabidopsis, the best studied Pattern-triggered immunity (PTI) system is perception of the bacterial pathogen-associated molecular pattern (PAMP) flagellin, or its active peptide-derivative flg22, by the plasma membrane-localized receptor FLAGELLIN SENSING 2 (FLS2). Flg22 perception initiates an array of immune responses including the fast and transient production of reactive oxygen species (ROS). In addition, FLS2 undergoes ligand-induced endocytosis and subsequent degradation within 60 min of flg22-treatment.

Luminol-based assays are routinely used to measure extracellular ROS production within minutes after flg22 treatment. Many mutants in flg22-response pathways display defects in flg22-induced ROS production. Here, we describe a luminol-based ROS Re-elicitation Assay that can be utilized to quantitatively assess flg22-signaling competency of FLS2 at times during which FLS2 is internalized, trafficked through endosomal compartments, and degraded in response to flg22. This assay may also be employed to correlate FLS2 signaling competency with receptor accumulation in vesicular trafficking mutants that either affect FLS2 endocytosis or replenishment of FLS2 through the secretory pathway. In addition, this assay can be extended to studies of other PAMP (ligand)–receptor pairs.


Via Christophe Jacquet
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Science: Genomic-scale exchange of mRNA between a parasitic plant and its hosts (2014)

Science: Genomic-scale exchange of mRNA between a parasitic plant and its hosts (2014) | Plant-Microbe Interaction | Scoop.it

Movement of RNAs between cells of a single plant is well documented, but cross-species RNA transfer is largely unexplored. Cuscuta pentagona (dodder) is a parasitic plant that forms symplastic connections with its hosts and takes up host messenger RNAs (mRNAs). We sequenced transcriptomes of Cuscuta growing on Arabidopsis and tomato hosts to characterize mRNA transfer between species and found that mRNAs move in high numbers and in a bidirectional manner. The mobile transcripts represented thousands of different genes, and nearly half the expressed transcriptome of Arabidopsis was identified in Cuscuta. These findings demonstrate that parasitic plants can exchange large proportions of their transcriptomes with hosts, providing potential mechanisms for RNA-based interactions between species and horizontal gene transfer.


Via Kamoun Lab @ TSL
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The role of effectors and host immunity in plant–necrotrophic fungal interactions

The role of effectors and host immunity in plant–necrotrophic fungal interactions | Plant-Microbe Interaction | Scoop.it

Fungal diseases pose constant threats to the global economy and food safety. As the largest group of plant fungal pathogens, necrotrophic fungi cause heavy crop losses worldwide. The molecular mechanisms of the interaction between necrotrophic fungi and plants are complex and involve sophisticated recognition and signaling networks. Here, we review recent findings on the roles of phytotoxin and proteinaceous effectors, pathogen-associated molecular patterns (PAMPs), and small RNAs from necrotrophic fungi. We also consider the functions of damage-associated molecular patterns (DAMPs), the receptor-like protein kinase BIK1, and epigenetic regulation in plant immunity to necrotrophic fungi.


Via Christophe Jacquet
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Evolution and Genomics

Evolution and Genomics | Plant-Microbe Interaction | Scoop.it

immersive training opportunities | The European Workshop on Genomics is being planned for January 2015 and will be held in Cesky Krumlov, Czech Republic. Updates coming soon! Please sign-up for our email list to be notified!


Via Chris Upton + helpers
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Lectin domains at the frontiers of plant defense

Lectin domains at the frontiers of plant defense | Plant-Microbe Interaction | Scoop.it
Plants are under constant attack from pathogens and herbivorous insects. To protect and defend themselves, plants evolved a multi-layered surveillance system, known as the innate immune system. Plants sense their encounters upon perception of conserved microbial structures and damage-associated patterns using cell-surface and intracellular immune receptors. Plant lectins and proteins with one or more lectin domains represent a major part of these receptors. The whole group of plant lectins comprises an elaborate collection of proteins capable of recognizing and interacting with specific carbohydrate structures, either originating from the invading organisms or from damaged plant cell wall structures. Due to the vast diversity in protein structures, carbohydrate recognition domains and glycan binding specificities, plant lectins constitute a very diverse protein superfamily. In the last decade, new types of nucleocytoplasmic plant lectins have been identified and characterized, in particular lectins expressed inside the nucleus and the cytoplasm of plant cells often as part of a specific plant response upon exposure to different stress factors or changing environmental conditions. In this review, we provide an overview on plant lectin motifs used in the constant battle against pathogens and predators during plant defenses.

Via Francis Martin, Christophe Jacquet
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A nonRD receptor-like kinase prevents nodule early senescence and defense-like reactions during symbiosis -

A nonRD receptor-like kinase prevents nodule early senescence and defense-like reactions during symbiosis - | Plant-Microbe Interaction | Scoop.it

Rhizobia and legumes establish symbiotic interactions leading to the production of root nodules, in which bacteria fix atmospheric nitrogen for the plant's benefit. This symbiosis is efficient because of the high rhizobia population within nodules. Here, we investigated how legumes accommodate such bacterial colonization.We used a reverse genetic approach to identify a Medicago truncatula gene, SymCRK, which encodes a cysteine-rich receptor-like kinase that is required for rhizobia maintenance within the plant cells, and performed detailed phenotypic analyses of the corresponding mutant.The Medicago truncatula symCRK mutant developed nonfunctional and necrotic nodules. A nonarginine asparate (nonRD) motif, typical of receptors involved in innate immunity, is present in the SymCRK kinase domain. Similar to the dnf2 mutant, bacteroid differentiation defect, defense-like reactions and early senescence were observed in the symCRK nodules. However, the dnf2 and symCRK nodules differ by their degree of colonization, which is higher in symCRK. Furthermore, in contrast to dnf2, symCRK is not a conditional mutant.These results suggest that in M. truncatula at least two genes are involved in the symbiotic control of immunity. Furthermore, phenotype differences between the two mutants suggest that two distinct molecular mechanisms control suppression of plant immunity during nodulation.


Via Christophe Jacquet
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Apoplastic peroxidases are required for salicylic acid-mediated defense against Pseudomonas syringae

Apoplastic peroxidases are required for salicylic acid-mediated defense against Pseudomonas syringae | Plant-Microbe Interaction | Scoop.it

Reactive oxygen species (ROS) generated by NADPH oxidases or apoplastic peroxidases play an important role in the plant defense response. Diminished expression of at least two Arabidopsis thaliana peroxidase encoding genes, PRX33 (At3g49110) and PRX34 (At3g49120), as a consequence of anti-sense expression of a heterologous French bean peroxidase gene (asFBP1.1), were previously shown to result in reduced levels of ROS following pathogen attack, enhanced susceptibility to a variety of bacterial and fungal pathogens, and reduced levels of callose production and defense-related gene expression in response to the microbe associated molecular pattern (MAMP) molecules flg22 and elf26. These data demonstrated that the peroxidase-dependent oxidative burst plays an important role in the elicitation of pattern-triggered immunity (PTI). Further work reported in this paper, however, shows that asFBP1.1 antisense plants are not impaired in all PTI-associated responses. For example, some but not all flg22-elicited genes are induced to lower levels by flg22 in asFPB1.1, and callose deposition in asFPB1.1 is similar to wild-type following infiltration with a Pseudomonas syringae hrcC mutant or with non-host P. syringae pathovars. Moreover, asFPB1.1 plants did not exhibit any apparent defect in their ability to mount a hypersensitive response (HR). On the other hand, salicylic acid (SA)-mediated activation of PR1 was dramatically impaired in asFPB1.1 plants. In addition, P. syringae-elicited expression of many genes known to be SA-dependent was significantly reduced in asFBP1.1 plants. Consistent with this latter result, in asFBP1.1 plants the key regulator of SA-mediated responses, NPR1, showed both dramatically decreased total protein abundance and a failure to monomerize, which is required for its translocation into the nucleus.


Via Christophe Jacquet
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Facility-Specific “House” Microbiome Drives Microbial Landscapes of Artisan Cheesemaking Plants

Facility-Specific “House” Microbiome Drives Microbial Landscapes of Artisan Cheesemaking Plants | Plant-Microbe Interaction | Scoop.it

Cheese fermentations involve the growth of complex microbial consortia, which often originate in the processing environment and drive the development of regional product qualities. However, the microbial milieus of cheesemaking facilities are largely unexplored and the true nature of the fermentation-facility relationship remains nebulous. Thus, a high-throughput sequencing approach was employed to investigate the microbial ecosystems of two artisanal cheesemaking plants, with the goal of elucidating how the processing environment influences microbial community assemblages. Results demonstrate that fermentation-associated microbes dominated most surfaces, primarilyDebaryomyces and Lactococcus, indicating that establishment of these organisms on processing surfaces may play an important role in microbial transfer, beneficially directing the course of sequential fermentations. Environmental organisms detected in processing environments dominated the surface microbiota of washed-rind cheeses maturing in both facilities, demonstrating the importance of the processing environment for populating cheese microbial communities, even in inoculated cheeses. Spatial diversification within both facilities reflects the functional adaptations of microbial communities inhabiting different surfaces and the existence of facility-specific “house” microbiota, which may play a role in shaping site-specific product characteristics.


Via Francis Martin
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Long-Term Evolution of Nucleotide-Binding Site-Leucine-Rich Repeat (NBS-LRR) Genes: Understandings Gained From and Beyond the Legume Family

Long-Term Evolution of Nucleotide-Binding Site-Leucine-Rich Repeat (NBS-LRR) Genes: Understandings Gained From and Beyond the Legume Family | Plant-Microbe Interaction | Scoop.it

Proper utilization of plant disease resistance genes requires a good understanding of their short and long-term evolution. Here, we present a comprehensive study on the long-term evolutionary history of Nucleotide-Binding Site-Leucine-Rich Repeat (NBS-LRR) genes within and beyond the legume family. The small group of NBS-LRR genes with N-terminal RPW8-like domain (referred to as RNL) was first revealed as a basal clade sister to both CC-NBS-LRR (CNL) and TIR-NBS-LRR (TNL) clades. Using Arabidopsis as an “outgroup”, this study explicitly recovered 31 ancestral NBS lineages (2 RNL, 21 CNL, and 8 TNL) that had existed in the Rosid common ancestor and 119 ancestral lineages (9 RNL, 55 CNL, and 55 TNL) that had diverged in the legume common ancestor. It was shown that, during their evolution in the past 54 million years, approximately 94% (112/119) of the ancestral legume NBS lineages experienced deletions or significant expansions while seven original lineages were maintained in a conservative manner. The NBS gene duplication pattern was further examined. The local tandem duplications dominated NBS gene gains in the total number of genes (more than 75%), which was not surprising. However, it was interesting to note from our study that ectopic duplications had created many novel NBS gene loci in individual legume genomes, which occurred at a significant frequency of 8 to 20% in different legume lineages. Finally, by surveying the legume microRNAs that can potentially regulate NBS genes, we found that the microRNA-NBS gene interaction also exhibited a “gain and loss” pattern during the legume evolution.


Via Christophe Jacquet
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AvrXa7-Xa7 Mediated Defense in Rice Can Be Suppressed by Transcriptional Activator-Like Effectors TAL6 and TAL11a from Xanthomonas oryzae pv. oryzicola - Mol. Plant-Microbe Interact.

AvrXa7-Xa7 Mediated Defense in Rice Can Be Suppressed by Transcriptional Activator-Like Effectors TAL6 and TAL11a from Xanthomonas oryzae pv. oryzicola - Mol. Plant-Microbe Interact. | Plant-Microbe Interaction | Scoop.it

(via T. Lahaye, thx)

Ji et al, 2014

The closely related plant pathogens Xanthomonas oryzae pv. oryzicola and X. oryzae pv. oryzae cause bacterial leaf streak (BLS) and bacterial leaf blight (BLB), respectively, in rice. Unlike X. oryzae pv. oryzae, endogenous avirulence-resistance (avr-R) gene interactions have not been identified in the X. oryzae pv. oryzicola–rice pathosystem, though both X. oryzae pv. oryzicola and X. oryzae pv. oryzae possess transcriptional activator-like effectors (TALE), which are known to modulate R or S genes in rice. In this report, avrXa7, avrXa10, and avrXa27 from X. oryzae pv. oryzae were transferred into YNB0-17 and RS105, hypovirulent and hypervirulent strains, respectively, of X. oryzae pv. oryzicola. When YNB0-17 containing avrXa7, avrXa10, or avrXa27 was inoculated to rice, hypersensitive responses (HR) were elicited in rice cultivars containing the R genes Xa7, Xa10, and Xa27, respectively. By contrast, RS105 expressing avrXa27 elicited an HR in a rice cultivar containing Xa27 but the expression of avrXa7 and avrXa10 in RS105 did not result in HR in rice cultivars containing Xa7 and Xa10, correspondingly. Southern blot analysis demonstrated that YNB0-17 possesses only approximately nine putative tale genes, whereas the hypervirulent RS105 contains at least 20. Although YNB0-17 contains an intact type III secretion system (T3SS), its genome is lacking the T3SS effector genes avrRxo1 and xopO, which are present in RS105. The introduction of avrRxo1 and xopO into YNB0-17 did not suppress avrXa7- or avrXa10-triggered immunity in rice. However, the transference of individual tale genes from RS105 into YNB0-17 led to the identification of tal6 and tal11a that suppressed avrXa7-Xa7-mediated defense. Thus, YNB0-17 may be a useful recipient for discovering such suppressors. This is the first report that co-evolutionally generated tale genes in X. oryzae pv. oryzicola suppress gene-for-gene defense against BLB, which may explain the lack of BLS-resistant cultivars.


Via dromius
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C-Sibelia: an easy-to-use and highly accurate tool for bacterial genome comparison

C-Sibelia: an easy-to-use and highly accurate tool for bacterial genome comparison | Plant-Microbe Interaction | Scoop.it

We present C-Sibelia, a highly accurate and easy-to-use software tool for comparing two closely related bacterial genomes, which can be presented as either finished sequences or fragmented assemblies. C-Sibelia takes as input two FASTA files and produces: (1) a VCF file containing all identified single nucleotide variations and indels; (2) an XMFA file containing alignment information. The software also produces Circos diagrams visualizing high level genomic architecture for rearrangement analyses. C-Sibelia is a part of the Sibelia comparative genomics suite, which is freely available under the GNU GPL v.2 license at http://sourceforge.net/projects/sibelia-bio. C-Sibelia is compatible with Unix-like operating systems. A web-based version of the software is available at http://etool.me/software/csibelia.


Via Niklaus Grunwald
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RAB11-mediated trafficking in host–pathogen interactions

Many bacterial and viral pathogens block or subvert host cellular processes to promote successful infection. One host protein that is targeted by invading pathogens is the small GTPase RAB11, which functions in vesicular trafficking. RAB11 functions in conjunction with a protein complex known as the exocyst to mediate terminal steps in cargo transport via the recycling endosome to cell–cell junctions, phagosomes and cellular protrusions. These processes contribute to host innate immunity by promoting epithelial and endothelial barrier integrity, sensing and immobilizing pathogens and repairing pathogen-induced cellular damage. In this Review, we discuss the various mechanisms that pathogens have evolved to disrupt or subvert RAB11-dependent pathways as part of their infection strategy.

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Arabidopsis ENHANCED DISEASE SUSCEPTIBILITY1 promotes systemic acquired resistance via azelaic acid and its precursor 9-oxo nonanoic acid

Arabidopsis ENHANCED DISEASE SUSCEPTIBILITY1 promotes systemic acquired resistance via azelaic acid and its precursor 9-oxo nonanoic acid | Plant-Microbe Interaction | Scoop.it

Systemic acquired resistance (SAR) is a form of inducible disease resistance that depends on salicylic acid and its upstream regulator ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1). Although local Arabidopsis thaliana defence responses activated by the Pseudomonas syringae effector protein AvrRpm1 are intact in eds1 mutant plants, SAR signal generation is abolished. Here, the SAR-specific phenotype of the eds1 mutant is utilized to identify metabolites that contribute to SAR. To this end, SAR bioassay-assisted fractionation of extracts from the wild type compared with eds1 mutant plants that conditionally express AvrRpm1 was performed. Using high-performance liquid chromatography followed by mass spectrometry, systemic immunity was associated with the accumulation of 60 metabolites, including the putative SAR signal azelaic acid (AzA) and its precursors 9-hydroperoxy octadecadienoic acid (9-HPOD) and 9-oxo nonanoic acid (ONA). Exogenous ONA induced SAR in systemic untreated leaves when applied at a 4-fold lower concentration than AzA. The data suggest that in planta oxidation of ONA to AzA might be partially responsible for this response and provide further evidence that AzA mobilizes Arabidopsis immunity in a concentration-dependent manner. The AzA fragmentation product pimelic acid did not induce SAR. The results link the C9 lipid peroxidation products ONA and AzA with systemic rather than local resistance and suggest that EDS1 directly or indirectly promotes the accumulation of ONA, AzA, or one or more of their common precursors possibly by activating one or more pathways that either result in the release of these compounds from galactolipids or promote lipid peroxidation.


Via Christophe Jacquet
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Structural basis for the recruitment and activation of the Legionella phospholipase VipD by the host GTPase Rab5

Structural basis for the recruitment and activation of the Legionella phospholipase VipD by the host GTPase Rab5 | Plant-Microbe Interaction | Scoop.it

A challenge for microbial pathogens is to assure that their translocated effector proteins target only the correct host cell compartment during infection. The Legionella pneumophila effector vacuolar protein sorting inhibitor protein D (VipD) localizes to early endosomal membranes and alters their lipid and protein composition, thereby protecting the pathogen from endosomal fusion. This process requires the phospholipase A1 (PLA1) activity of VipD that is triggered specifically on VipD binding to the host cell GTPase Rab5, a key regulator of endosomes. Here, we present the crystal structure of VipD in complex with constitutively active Rab5 and reveal the molecular mechanism underlying PLA1 activation. An active site-obstructing loop that originates from the C-terminal domain of VipD is repositioned on Rab5 binding, thereby exposing the catalytic pocket within the N-terminal PLA1 domain. Substitution of amino acid residues located within the VipD–Rab5 interface prevented Rab5 binding and PLA1 activation and caused a failure of VipD mutant proteins to target to Rab5-enriched endosomal structures within cells. Experimental and computational analyses confirmed an extended VipD-binding interface on Rab5, explaining why this L. pneumophila effector can compete with cellular ligands for Rab5 binding. Together, our data explain how the catalytic activity of a microbial effector can be precisely linked to its subcellular localization.

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Go in for the kill: How plants deploy effector-triggered immunity to combat pathogens

Go in for the kill: How plants deploy effector-triggered immunity to combat pathogens | Plant-Microbe Interaction | Scoop.it

Plant resistance (R) proteins perceive specific pathogen effectors from diverse plant pathogens to initiate defense responses, designated effector-triggered immunity (ETI). Plant R proteins are mostly nucleotide binding-leucine rich repeat (NB-LRR) proteins, which recognize pathogen effectors directly or indirectly through sophisticated mechanisms. Upon activation by effector proteins, R proteins elicit robust defense responses, including a rapid burst of reactive oxygen species (ROS), induced biosynthesis and accumulation of salicylic acid (SA), a rapid programmed cell death (PCD) called hypersensitive response (HR) at the infection sites, and increased expression of pathogenesis-related (PR) genes. Initiation of ETI is correlated with a complex network of defense signaling pathways, resulting in defensive cellular responses and large-scale transcriptional reprogramming events. In this review, we highlight important recent advances on the recognition of effectors, regulation and activation of plant R proteins, dynamic intracellular trafficking of R proteins, induction of cell death, and transcriptional reprogramming associated with ETI. Current knowledge gaps and future research directions are also discussed in this review.


Via Christophe Jacquet
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The perplexing role of autophagy in plant innate immune responses

The perplexing role of autophagy in plant innate immune responses | Plant-Microbe Interaction | Scoop.it

Autophagy is a major intracellular process for the degradation of cytosolic macromolecules and organelles in the lysosomes or vacuoles for the purposes of regulating cellular homeostasis and protein and organelle quality control. In complex metazoan organisms, autophagy is highly engaged during the immune responses through interfaces either directly with intracellular pathogens or indirectly with immune signalling molecules. Studies over the last decade or so have also revealed a number of important ways in which autophagy shapes plant innate immune responses. First, autophagy promotes defence-associated hypersensitive cell death induced by avirulent or related pathogens, but restricts unnecessary or disease-associated spread of cell death. This elaborate regulation of plant host cell death by autophagy is critical during plant immune responses to the types of plant pathogens that induce cell death, which include avirulent biotrophic pathogens and necrotrophic pathogens. Second, autophagy modulates defence responses regulated by salicylic acid and jasmonic acid, thereby influencing plant basal resistance to both biotrophic and necrotrophic pathogens. Third, there is an emerging role of autophagy in virus-induced RNA silencing, either as an antiviral collaborator for targeted degradation of viral RNA silencing suppressors or an accomplice of viral RNA silencing suppressors for targeted degradation of key components of plant cellular RNA silencing machinery. In this review, we summarize this important progress and discuss the potential significance of the perplexing role of autophagy in plant innate immunity.


Via Christophe Jacquet
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Special Issue: Small molecules: from structural diversity to signalling and regulatory roles - The Plant Journal

Special Issue: Small molecules: from structural diversity to signalling and regulatory roles - The Plant Journal | Plant-Microbe Interaction | Scoop.it

Despite the many challenges in detecting and functionally characterizing small molecules, genomics advances paired with increasingly sophisticated metabolomics approaches have led to a steady increase in the discovery of metabolites of diverse structure and roles in signaling and regulatory processes. This special issue will highlight recent advances and discoveries in the field of small molecule research ranging from signaling metabolites in primary metabolism to molecules with roles in inter- or intra-specific interactions in plants and algae. The reader will find traditional functional classifications of small molecules to become increasingly blurred since many chemicals act as exogenous signals and simultaneously serve important endogenous functions in plant physiology and development.


Via Francis Martin, Mary Williams
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Rice SAPs are responsive to multiple biotic stresses and overexpression of OsSAP1, an A20/AN1 zinc-finger protein, enhances the basal resistance against pathogen infection in tobacco

Rice SAPs are responsive to multiple biotic stresses and overexpression of OsSAP1, an A20/AN1 zinc-finger protein, enhances the basal resistance against pathogen infection in tobacco | Plant-Microbe Interaction | Scoop.it

Highlights•

Expression patterns of 18 OsSAPs analysed in response to biotic stress simulators.

OsSAP1 enhanced the basal resistance against pathogen in tobacco plants.

OsSAP1 modulated the expression of biotic stress related genes.

Rice SAPs may be involved in host defence response and biotic stress tolerance.

Abstract

Eukaryotic A20/AN1 zinc-finger proteins (ZFPs) play an important role in the regulation of immune and stress response. After elucidation of the role of first such protein, OsSAP1, in abiotic stress tolerance, 18 rice stress associated protein (SAP) genes have been shown to be regulated by multiple abiotic stresses. In the present study, expression pattern of all the 18 OsSAP genes have been analysed in response to different biotic stress simulators, in order to get insights into their possible involvement in biotic stress tolerance. Our results showed the upregulation of OsSAP1 and OsSAP11 by all biotic stress simulator treatments. Furthermore, the functional role of OsSAP1 in plant defence responses has been explored through overexpression in transgenic plants. Constitutive expression of OsSAP1 in transgenic tobacco resulted into enhanced disease resistance against virulent bacterial pathogen, together with the upregulation of known defence-related genes. Present investigation suggests that rice SAPs are responsive to multiple biotic stresses and OsSAP1 plays a key role in basal resistance against pathogen infection. This strongly supports the involvement of rice SAPs in cross-talk between biotic and abiotic stress signalling pathways, which makes them ideal candidate to design strategies for protecting crop plants against multiple stresses.


Via Christophe Jacquet
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Frontiers | Killing two birds with one stone: trans-kingdom suppression of PAMP/MAMP-induced immunity by T3E from enteropathogenic bacteria | Plant-Microbe Interaction

Frontiers | Killing two birds with one stone: trans-kingdom suppression of PAMP/MAMP-induced immunity by T3E from enteropathogenic bacteria | Plant-Microbe Interaction | Plant-Microbe Interaction | Scoop.it
Within the past decade, remarkable similarities between the molecular organization of animal and plant systems for non-self discrimination were revealed. Obvious parallels exist between the molecular structures of the receptors mediating the recognition of pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs) with plant pattern recognition receptors (PRRs) strikingly resembling mammalian Toll-like receptors. Mitogen-activated protein (MAP) kinase cascades, leading to the transcriptional activation of immunity-associated genes, illustrate the conservation of whole molecular building blocks of PAMP/MAMP-induced signaling. Enteropathogenic Salmonella and Escherichia coli use a type three secretion system (T3SS) to inject effector proteins into the mammalian host cell to subvert defense mechanisms and promote gut infection. Lately, disease occurrence was increasingly associated with bacteria-contaminated fruits and vegetables and common themes have emerged with regard to whether and how effectors target innate immune responses in a trans-kingdom manner. We propose that numerous Salmonella or E. coli effectors may be active in planta and tend to target central components (hubs) of immune signaling pathways.

Via Christophe Jacquet
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Rescooped by Guogen Yang from MycorWeb Plant-Microbe Interactions
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A Distinct Role of Pectate Lyases in the Formation of Feeding Structures Induced by Cyst and Root-Knot Nematodes

A Distinct Role of Pectate Lyases in the Formation of Feeding Structures Induced by Cyst and Root-Knot Nematodes | Plant-Microbe Interaction | Scoop.it

Pectin in the primary plant cell wall is thought to be responsible for its porosity, charge density, and microfibril spacing and is the main component of the middle lamella. Plant-parasitic nematodes secrete cell wall–degrading enzymes that macerate the plant tissue, facilitating the penetration and migration within the roots. In sedentary endoparasitic nematodes, these enzymes are released only during the migration of infective juveniles through the root. Later, nematodes manipulate the expression of host plant genes, including various cell wall enzymes, in order to induce specific feeding sites. In this study, we investigated expression of two Arabidopsis pectate lyase-like genes (PLL), PLL18(At3g27400) and PLL19 (At4g24780), together with pectic epitopes with different degrees of methylesterification in both syncytia induced by the cyst nematode Heterodera schachtii and giant cells induced by the root-knot nematode Meloidogyne incognita. We confirmed upregulation ofPLL18 and PLL19 in both types of feeding sites with quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) and in situ RT-PCR. Furthermore, the functional analysis of mutants demonstrated the important role of both PLL genes in the development and maintenance of syncytia but not giant cells. Our results show that both enzymes play distinct roles in different infected root tissues as well as during parasitism of different nematodes.


Via Francis Martin
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Rescooped by Guogen Yang from Plants and Microbes
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Annu Rev Phytopathology: Horizontal Gene Transfer in Eukaryotic Plant Pathogens (2014)

Annu Rev Phytopathology: Horizontal Gene Transfer in Eukaryotic Plant Pathogens (2014) | Plant-Microbe Interaction | Scoop.it

Gene transfer has been identified as a prevalent and pervasive phenomenon and an important source of genomic innovation in bacteria. The role of gene transfer in microbial eukaryotes seems to be of a reduced magnitude but in some cases can drive important evolutionary innovations, such as new functions that underpin the colonization of different niches. The aim of this review is to summarize published cases that support the hypothesis that horizontal gene transfer (HGT) has played a role in the evolution of phytopathogenic traits in fungi and oomycetes. Our survey of the literature identifies 46 proposed cases of transfer of genes that have a putative or experimentally demonstrable phytopathogenic function. When considering the life-cycle steps through which a pathogen must progress, the majority of the HGTs identified are associated with invading, degrading, and manipulating the host. Taken together, these data suggest HGT has played a role in shaping how fungi and oomycetes colonize plant hosts.


Via Francis Martin, Kamoun Lab @ TSL
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Rescooped by Guogen Yang from Plant-microbe interactions (on the plant's side)
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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-Microbe Interaction | 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 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. Green fluorescent protein-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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