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Rescooped by Xiaodong Wang from Plant immunity and legume symbiosis
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A Framework for Lateral Membrane Trafficking and Polar Tethering of the PEN3 ATP-Binding Cassette Transporter

A Framework for Lateral Membrane Trafficking and Polar Tethering of the PEN3 ATP-Binding Cassette Transporter | Cereal and Biotrophic Pathogens | Scoop.it
The outermost cell layer of plants, the epidermis, and its outer (lateral) membrane domain facing the environment are continuously challenged by biotic and abiotic stresses. Therefore, the epidermis and the outer membrane domain provide important selective and protective barriers. However, only a small number of specifically outer membrane-localized proteins are known. Similarly, molecular mechanisms underlying the trafficking and the polar placement of outer membrane domain proteins require further exploration. Here, we demonstrate that ACTIN7 (ACT7) mediates trafficking of the PENETRATION3 (PEN3) outer membrane protein from the trans-Golgi network (TGN) to the plasma membrane in the root epidermis of Arabidopsis (Arabidopsis thaliana) and that actin function contributes to PEN3 endocytic recycling. In contrast to such generic ACT7-dependent trafficking from the TGN, the EXOCYST84b (EXO84b) tethering factor mediates PEN3 outer-membrane polarity. Moreover, precise EXO84b placement at the outer membrane domain itself requires ACT7 function. Hence, our results uncover spatially and mechanistically distinct requirements for ACT7 function during outer lateral membrane cargo trafficking and polarity establishment. They further identify an exocyst tethering complex mediator of outer lateral membrane cargo polarity.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant pathogens and pests
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Frontiers | Engineering Plant Immunity: Using CRISPR/Cas9 to Generate Virus Resistance | Plant Biotechnology

Frontiers | Engineering Plant Immunity: Using CRISPR/Cas9 to Generate Virus Resistance | Plant Biotechnology | Cereal and Biotrophic Pathogens | Scoop.it
Plant viruses infect many economically important crops, including wheat, cotton, maize, cassava, and other vegetables. These viruses pose a serious threat to agriculture worldwide, as decreases in cropland area per capita may cause production to fall short of that required to feed the increasing world population. Under these circumstances, conventional strategies can fail to control rapidly evolving and emerging plant viruses. Genome-engineering strategies have recently emerged as promising tools to introduce desirable traits in many eukaryotic species, including plants. Among these genome engineering technologies, the CRISPR (clustered regularly interspaced palindromic repeats)/CRISPR-associated 9 (CRISPR/Cas9) system has received special interest because of its simplicity, efficiency, and reproducibility. Recent studies have used CRISPR/Cas9 to engineer virus resistance in plants, either by directly targeting and cleaving the viral genome, or by modifying the host plant genome to introduce viral immunity. Here, we briefly describe the biology of the CRISPR/Cas9 system and plant viruses, and how different genome engineering technologies have been used to target these viruses. We further describe the main findings from recent studies of CRISPR/Cas9-mediated viral interference and discuss how these findings can be applied to improve global agriculture. We conclude by pinpointing the gaps in our knowledge and the outstanding questions regarding CRISPR/Cas9-mediated viral immunity.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant immunity and legume symbiosis
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Frontiers | The Mechanisms of Maize Resistance to Fusarium verticillioides by Comprehensive Analysis of RNA-seq Data | Crop Science and Horticulture

Frontiers | The Mechanisms of Maize Resistance to Fusarium verticillioides by Comprehensive Analysis of RNA-seq Data | Crop Science and Horticulture | Cereal and Biotrophic Pathogens | Scoop.it
Fusarium verticillioides is the most commonly reported fungal species responsible for ear rot of maize which substantially reduces grain yield. It also results in a substantial accumulation of mycotoxins that give rise to toxic response when ingested by animals and humans. For inefficient control by chemical and agronomic measures, it thus becomes more desirable to select more resistant varieties. However, the molecular mechanisms underlying the infection process remain poorly understood, which hampers the application of quantitative resistance in breeding programs. Here, we reveal the disease-resistance mechanism of the maize inbred line of BT-1 which displays high resistance to ear rot using RNA high throughput sequencing. By analyzing RNA-seq data from the BT-1 kernels before and after F. verticillioides inoculation, we found that transcript levels of genes associated with key pathways are dramatically changed compared with the control treatment. Differential gene expression in ear rot resistant and susceptible maize was confirmed by RNA microarray and qRT-PCR analyses. Further investigation suggests that the small heat shock protein family, some secondary metabolites, and the signaling pathways of abscisic acid, jasmonic acid, or salicylic acids (SA) may be involved in the pathogen-associated molecular pattern-triggered immunity against F. verticillioides. These data will not only provide new insights into the molecular resistant mechanisms against fungi invading, but may also result in the identification of key molecular factors associated with ear rot resistance in maize.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant pathogens and pests
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Nicotiana benthamiana as a nonhost of Zymoseptoria tritici

Nicotiana benthamiana as a nonhost of Zymoseptoria tritici | Cereal and Biotrophic Pathogens | Scoop.it
In nature, plants are continually being bombarded by microbes. However, actual host–pathogen interactions that negatively affect (result in disease) any given plant species are by far the exception, rather than the rule. The plant protection mechanism effective against this plethora of microbes that lack pathogenicity is classified as nonhost resistance (NHR) and is the most common and effective form of plant resistance in nature. However, compared to actual host–pathogen interactions for which a vast amount of knowledge regarding plant defense, pathogen evasion of host detection, and host manipulation has been developed, interactions involving NHR are much less studied and, therefore, less understood. Knowledge of NHR has the potential to provide novel control strategies for pathogens that are currently difficult to combat. In this issue of New Phytologist, the Rothamsted Research laboratories of Jason Rudd and Kostya Kanyuka (Kettles et al., pp. 338–350) make considerable progress toward the characterization of the NHR response to the important wheat pathogen Zymoseptoria tritici using the model plant Nicotiana benthamiana.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant pathogens and pests
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The appressorium of the rice blast fungus Magnaporthe oryzae remains mitotically active during post-penetration hyphal growth

The appressorium of the rice blast fungus Magnaporthe oryzae remains mitotically active during post-penetration hyphal growth | Cereal and Biotrophic Pathogens | Scoop.it
Highlights • M. oryzae appressoria remain mitotically active during IH proliferation. • Sister chromatids separate within the appressorium. • A mitotic nucleus undergoes extreme constriction and elongation through the penetration peg. Abstract To investigate the mitotic dynamics of an appressorium, we used live-cell confocal imaging of a fluorescence-based mitotic reporter strain of Magnaporthe oryzae. We present evidence that the M. oryzae appressorium remains viable and mitotically active well after host penetration. These results suggest the potential roles of the appressorium during post-penetration proliferation of invasive hyphae. Our studies also revealed that a mitotic appressorial nucleus undergoes extreme constriction and elongation as it migrates through the penetration peg in a manner analogous to mitosis during cell-to-cell movement of invasive hyphae. Understanding the mechanisms underlying these pathogen-specific nuclear dynamics may provide new targets for disease control.

Via Elsa Ballini, Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant immunity and legume symbiosis
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An E3 Ligase Affects the NLR Receptor Stability and Immunity to Powdery Mildew

An E3 Ligase Affects the NLR Receptor Stability and Immunity to Powdery Mildew | Cereal and Biotrophic Pathogens | Scoop.it
Following the detection of pathogen cognate effectors, plant Nod-like receptors (NLRs) trigger isolate-specific immunity that is generally associated with cell death. The regulation of NLR stability is important to ensure effective immunity. In barley (Hordeum vulgare), the allelic Mildew locus A (MLA) receptors mediate isolate-specific disease resistance against powdery mildew fungus (Blumeria graminis f. sp. hordei). Currently, how MLA stability is controlled remains unknown. Here, we identified an MLA-interacting RING-type E3 ligase, MIR1, that interacts with several MLAs. We showed that the carboxyl-terminal TPR domain of MIR1 mediates the interaction with the coiled-coil domain-containing region of functional MLAs, such as MLA1, MLA6, and MLA10, but not with that of the nonfunctional MLA18-1. MIR1 can ubiquitinate the amino-terminal region of MLAs in vitro and promotes the proteasomal degradation of MLAs in vitro and in planta. Both proteasome inhibitor treatment and virus-induced gene silencing-mediated MIR1 silencing significantly increased MLA abundance in barley transgenic lines. Furthermore, overexpression of MIR1 specifically compromised MLA-mediated disease resistance in barley, while coexpression of MIR1 and MLA10 attenuated MLA10-induced cell death signaling in Nicotiana benthamiana. Together, our data reveal a mechanism for the control of the stability of MLA immune receptors and for the attenuation of MLA-triggered defense signaling by a RING-type E3 ligase via the ubiquitin proteasome system.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant immunity and legume symbiosis
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Chitin receptor CERK1 links salt stress and chitin‐triggered innate immunity in Arabidopsis

Chitin receptor CERK1 links salt stress and chitin‐triggered innate immunity in Arabidopsis | Cereal and Biotrophic Pathogens | Scoop.it
In nature, plants need to respond to multiple environmental stresses that require involvement and fine-tuning of different stress signaling pathways. Cross-tolerance in which plants pre-treated with chitin (a fungal microbe-associated molecular pattern) have improved salt tolerance was observed in Arabidopsis but is not well understood. Here, we show a unique link between chitin and salt signaling mediated by the chitin receptor CHITIN ELICITOR RECEPTOR KINASE 1 (CERK1). Transcriptome analysis revealed that salt stress-induced genes are highly correlated with chitin-induced genes, while this was not observed with other microbe-associated molecular patterns (MAMP) or with other abiotic stresses. The cerk1 mutant was more susceptible to NaCl than wild type. cerk1 plants had an irregular increase of cytosolic calcium ([Ca2+]cyt) after NaCl treatment. Bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation experiments indicated that CERK1 physically interacts with ANNEXIN 1 (ANN1), which was reported to form a calcium-permeable channel that contributes to the NaCl-induced [Ca2+]cyt signal. In turn, ann1 mutants showed elevated chitin-induced rapid responses. In short, molecular components previously shown to function in chitin or salt signaling physically interact and intimately link the downstream responses to fungal attack and salt stress.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant immunity and legume symbiosis
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Should I fight or should I grow now? The role of cytokinins in plant growth and immunity and in the growth–defence trade-off

Should I fight or should I grow now? The role of cytokinins in plant growth and immunity and in the growth–defence trade-off | Cereal and Biotrophic Pathogens | Scoop.it
Background Perception and activation of plant immunity require a remarkable level of signalling plasticity and control. In Arabidopsis and other plant species, constitutive defence activation leads to resistance to a broad spectrum of biotrophic pathogens, but also frequently to stunted growth and reduced seed set. Plant hormones are important integrators of the physiological responses that influence the outcome of plant–pathogen interactions.

Scope We review the mechanisms by which the plant hormone cytokinin regulates both plant growth and response to pathogens, and how cytokinins may connect these two processes, ultimately affecting the growth trade-offs observed in plant immunity.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant Pathogenomics
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BMC Genomics: Diversity, evolution and expression profiles of histone acetyltransferases and deacetylases in oomycetes (2016)

BMC Genomics: Diversity, evolution and expression profiles of histone acetyltransferases and deacetylases in oomycetes (2016) | Cereal and Biotrophic Pathogens | Scoop.it

Background - Oomycetes are a group of fungus-like eukaryotes with diverse microorganisms living in marine, freshwater and terrestrial environments. Many of them are important pathogens of plants and animals, causing severe economic losses. Based on previous study, gene expression in eukaryotic cells is regulated by epigenetic mechanisms such as DNA methylation and histone modification. However, little is known about epigenetic mechanisms of oomycetes.

 

Results - In this study, we investigated the candidate genes in regulating histone acetylation in oomycetes genomes through bioinformatics approaches and identified a group of diverse histone acetyltransferases (HATs) and histone deacetylases (HDACs), along with three putative novel HATs. Phylogenetic analyses suggested that most of these oomycetes HATs and HDACs derived from distinct evolutionary ancestors. Phylogenetic based analysis revealed the complex and distinct patterns of duplications and losses of HATs and HDACs in oomycetes. Moreover, gene expression analysis unveiled the specific expression patterns of the 33 HATs and 11 HDACs of Phytophthora infestans during the stages of development, infection and stress response.

 

Conclusions - In this study, we reveal the structure, diversity and the phylogeny of HATs and HDACs of oomycetes. By analyzing the expression data, we provide an overview of the specific biological stages of these genes involved. Our datasets provide useful inputs to help explore the epigenetic mechanisms and the relationship between genomes and phenotypes of oomycetes.


Via Kamoun Lab @ TSL
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Equiseticola gen. nov . ( Phaeosphaeriaceae ), from Equisetum sp. in Italy | ABD-ELSALAM | Phytotaxa

Equiseticola gen. nov . ( Phaeosphaeriaceae ), from Equisetum sp. in Italy | ABD-ELSALAM | Phytotaxa | Cereal and Biotrophic Pathogens | Scoop.it

This paper reports an interesting saprobic ascomycete which was collected and isolated from Equisetum sp. in Italy. The phylogeny of this taxon and genera of Phaeosphaeriaceae are constructed based on analyses of combined LSU, SSU and ITS sequence data. The species has exclusive characters such as ovoid ascomata with minute papilla, cylindrical asci with long acute or knob-like pedicel and fusiform, 4–5-septate, yellowish to pale brown ascospores. Based on phylogeny and morphology we introduce the taxon as a new genus and species within Phaeosphaeriaceae. The new genus and species are introduced with an illustrated account and compared with other taxa in Phaeosphaeriaceae.


Via Steve Marek
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Arabidopsis miR827 mediates post-transcriptional gene silencing of its ubiquitin E3 ligase target gene in the syncytium of the cyst nematode Heterodera schachtii to enhance susceptibility - Hewezi ...

Arabidopsis miR827 mediates post-transcriptional gene silencing of its ubiquitin E3 ligase target gene in the syncytium of the cyst nematode Heterodera schachtii to enhance susceptibility - Hewezi ... | Cereal and Biotrophic Pathogens | Scoop.it
MicroRNAs (miRNAs) are a major class of small non-coding RNAs with emerging functions in biotic and abiotic interactions. Here, we report on a new functional role of Arabidopsis miR827 and its NITROGEN LIMITATION ADAPTATION (NLA) target gene in mediating plant susceptibility to the beet cyst nematode Heterodera schachtii. Cyst nematodes are sedentary endoparasites that induce the formation of multinucleated feeding structures termed syncytia in the roots of host plants. Using promoter:GUS fusion assays we established that miR827 was activated in the initial feeding cells and this activation was maintained in the syncytium during all sedentary stages of nematode development. Meanwhile, the NLA target gene, which encodes an ubiquitin E3 ligase enzyme, was post-transcriptionally silenced in the syncytium to permanently suppress its activity during all nematode parasitic stages. Overexpression of miR827 in Arabidopsis resulted in hyper-susceptibility to H. schachtii. In contrast, inactivation of miR827 activity through target mimicry or by overexpression a miR827-resistant cDNA of NLA produced the opposite phenotype of reduced plant susceptibility to H. schachtii. Gene expression analysis of several pathogenesis-related genes together with Agrobacterium-mediated transient expression in Nicotiana benthamiana provided strong evidence that miR827-mediated downregulation of NLA to suppress basal defense pathways. In addition, using yeast two-hybrid screens we identified several candidates of NLA-interacting proteins that are involved in a wide range of biological processes and molecular functions, including three pathogenesis-related proteins. Taken together, we conclude that nematode-activated miR827 in the syncytium is necessary to suppress immune responses in order to establish infection and cause disease.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant pathogens and pests
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Resurgence of Less-Studied Smut Fungi as Models of Phytopathogenesis in the Omics Age | Phytopathology

Resurgence of Less-Studied Smut Fungi as Models of Phytopathogenesis in the Omics Age | Phytopathology | Cereal and Biotrophic Pathogens | Scoop.it
The smut fungi form a large, diverse, and nonmonophyletic group of plant pathogens that have long served as both important pests of human agriculture and, also, as fertile organisms of scientific investigation. As modern techniques of molecular genetic analysis became available, many previously studied species that proved refractive to these techniques fell by the wayside and were neglected. Now, as the advent of rapid and affordable next-generation sequencing provides genomic and transcriptomic resources for even these “forgotten” fungi, several species are making a comeback and retaking prominent places in phytopathogenic research. In this review, we highlight several of these smut fungi, with special emphasis on Microbotryum lychnidis-dioicae, an anther smut whose molecular genetic tools have finally begun to catch up with its historical importance in classical genetics and now provide mechanistic insights for ecological studies, evolution of host-pathogen interaction, and investigations of emerging infectious disease.


Via Steve Marek, Christophe Jacquet
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Dying two deaths — programmed cell death regulation in development and disease

Dying two deaths — programmed cell death regulation in development and disease | Cereal and Biotrophic Pathogens | Scoop.it
Programmed cell death (PCD) is a fundamental cellular process that has adopted a plethora of vital functions in multicellular organisms. In plants, PCD processes are elicited as an inherent part of regular development in specific cell types or tissues, but can also be triggered by biotic and abiotic stresses. Although over the last years we have seen progress in our understanding of the molecular regulation of different plant PCD processes, it is still unclear whether a common core machinery exists that controls cell death in development and disease. In this review, we discuss recent advances in the field, comparing some aspects of the molecular regulation controlling developmental and pathogen-triggered PCD in plants.

Via Tatsuya Nobori, Suayib Üstün
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Yr58: A New Stripe Rust Resistance Gene and Its Interaction with Yr46 for Enhanced Resistance | Phytopathology

Yr58: A New Stripe Rust Resistance Gene and Its Interaction with Yr46 for Enhanced Resistance | Phytopathology | Cereal and Biotrophic Pathogens | Scoop.it
The quantitative trait loci QYr.sun-3BS and QYr.sun-4DL were identified in the W195/BTSS recombinant inbred line (RIL) population in a previous study. QYr.sun-3BS explained 34 to 59% phenotypic variation in stripe rust response. We evaluated parental genotypes at different growth stages and temperature regimes to detect the critical stage for expression of QYr.sun-3BS. W195 expressed low infection type (IT) ;1C at the fourth leaf stage, when incubated at 21 ± 2°C and the alternate parent BTSS was susceptible (IT 3+). Monogenic segregation for stripe rust response was observed among the RIL population at the fourth leaf stage and the underlying locus was temporarily named YrW195. YrW195 corresponded to QYr.sun-3BS. Since no previously designated stripe rust resistance genes that expresses at and after the fourth leaf stage was mapped in this region, YrW195 was formally named Yr58. Genotyping with Yr46-linked markers indicated the presence of Yr46 in W195, which corresponded to QYr.sun-4DL. The RILs carrying Yr58 and Yr46 singly produced IT 23C and IT 3+, respectively, and those carrying both genes produced IT ;1C indicating the enhancement of Yr58 expression by Yr46. The absence of Yr58-linked alleles of markers sun533 and sun476 in 74 of the 76 wheat cultivars demonstrated their usefulness for marker-assisted selection.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant immunity and legume symbiosis
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Plasmodesmata enable multicellularity: new insights into their evolution, biogenesis, and functions in development and immunity

Plasmodesmata enable multicellularity: new insights into their evolution, biogenesis, and functions in development and immunity | Cereal and Biotrophic Pathogens | Scoop.it
Highlights 
• Recent phylogenies reveal that plasmodesmata evolved independently in land plants. 
• Plasmodesmatal biogenesis is controlled by several cellular signaling pathways. 
• Spatiotemporal control of PD coordinates signals that impact immunity. 

Plant cells are connected by plasmodesmata (PD), cytosolic bridges that allow molecules to freely move across the cell wall. Recently resolved relationships among land plants and their algal relatives reveal that land plants evolved PD independently from algae. Proteomic and genetic screens illuminate new dimensions of the structural and regulatory pathways that control PD biogenesis. Biochemical studies demonstrate that immunological signals induce systemic defenses by moving from diseased cells through PD; subsequently, PD transport is restricted to quarantine diseased cells. Here, we review our expanding knowledge of the roles of PD in plant development, physiology, and immunity.

Via Pierre-Marc Delaux, Christophe Jacquet
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Plant Virus Infection and the Ubiquitin Proteasome Machinery: Arms Race along the Endoplasmic Reticulum

Plant Virus Infection and the Ubiquitin Proteasome Machinery: Arms Race along the Endoplasmic Reticulum | Cereal and Biotrophic Pathogens | Scoop.it
The endoplasmic reticulum (ER) is central to plant virus replication, translation, maturation, and egress. Ubiquitin modification of ER associated cellular and viral proteins, alongside the actions of the 26S proteasome, are vital for the regulation of infection. Viruses can arrogate ER associated ubiquitination as well as cytosolic ubiquitin ligases with the purpose of directing the ubiquitin proteasome system (UPS) to new targets. Such targets include necessary modification of viral proteins which may stabilize certain complexes, or modification of Argonaute to suppress gene silencing. The UPS machinery also contributes to the regulation of effector triggered immunity pattern recognition receptor immunity. Combining the results of unrelated studies, many positive strand RNA plant viruses appear to interact with cytosolic Ub-ligases to provide novel avenues for controlling the deleterious consequences of disease. Viral interactions with the UPS serve to regulate virus infection in a manner that promotes replication and movement, but also modulates the levels of RNA accumulation to ensure successful biotrophic interactions. In other instances, the UPS plays a central role in cellular immunity. These opposing roles are made evident by contrasting studies where knockout mutations in the UPS can either hamper viruses or lead to more aggressive diseases. Understanding how viruses manipulate ER associated post-translational machineries to better manage virus–host interactions will provide new targets for crop improvement.

Via Christophe Jacquet
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Apoplastic recognition of multiple candidate effectors from the wheat pathogen Zymoseptoria tritici in the nonhost plant Nicotiana benthamiana

Apoplastic recognition of multiple candidate effectors from the wheat pathogen Zymoseptoria tritici in the nonhost plant Nicotiana benthamiana | Cereal and Biotrophic Pathogens | Scoop.it
The fungus Zymoseptoria tritici is a strictly apoplastic, host-specific pathogen of wheat leaves and causal agent of septoria tritici blotch (STB) disease. All other plants are considered nonhosts, but the mechanism of nonhost resistance (NHR) to Z. tritici has not been addressed previously. We sought to develop Nicotiana benthamiana as a system to study NHR against Z. tritici.
Fluorescence microscopy and quantitative reverse transcription polymerase chain reactions were used to establish the interaction between Z. tritici and N. benthamiana. Agrobacterium-mediated transient expression was used to screen putative Z. tritici effector genes for recognition in N. benthamiana, and virus-induced gene silencing (VIGS) was employed to determine the role of two receptor-like kinases (RLKs), NbBAK1 and NbSOBIR1, in Z. tritici effector recognition.
Numerous Z. tritici putative effectors (14 of 63 tested) induced cell death or chlorosis in N. benthamiana. For most, phenotypes were light-dependent and required effector secretion to the leaf apoplastic space. Moreover, effector-induced host cell death was dependent on NbBAK1 and NbSOBIR1.
Our results indicate widespread recognition of apoplastic effectors from a wheat-infecting fungal pathogen in a taxonomically distant nonhost plant species presumably by cell surface immune receptors. This suggests that apoplastic recognition of multiple nonadapted pathogen effectors may contribute to NHR.

Via Christophe Jacquet
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bioRxiv: NLR signaling network mediates immunity to diverse plant pathogens (2016)

bioRxiv: NLR signaling network mediates immunity to diverse plant pathogens (2016) | Cereal and Biotrophic Pathogens | Scoop.it

Plant and animal nucleotide-binding domain and leucine-rich repeat-containing (NLR) proteins often function in pairs to mediate innate immunity to pathogens. However, the degree to which NLR proteins form signaling networks beyond genetically linked pairs is poorly understood. In this study, we discovered that a large NLR immune signaling network with a complex genetic architecture confers immunity to oomycetes, bacteria, viruses, nematodes, and insects. The network emerged over 100 million years ago from a linked NLR pair that diversified into up to one half of the NLR of asterid plants. We propose that this NLR network increases robustness of immune signaling to counteract rapidly evolving plant pathogens.


Via Kamoun Lab @ TSL, Suayib Üstün
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MPMI: A Conserved Puccinia striiformis Protein Interacts with Wheat NPR1 and Reduces Induction of Pathogenesis-Related Genes in Response to Pathogens

MPMI: A Conserved Puccinia striiformis Protein Interacts with Wheat NPR1 and Reduces Induction of Pathogenesis-Related Genes in Response to Pathogens | Cereal and Biotrophic Pathogens | Scoop.it
In Arabidopsis, NPR1 is a key transcriptional co-regulator of systemic acquired resistance. Upon pathogen challenge, NPR1 translocates from the cytoplasm to the nucleus, where it interacts with TGA-bZIP transcription factors to activate the expression of several Pathogenesis-Related (PR) genes. In a screen of a yeast two-hybrid library from wheat leaves infected with Puccinia striiformis f. sp. tritici, we identified a conserved rust protein that interacts with wheat NPR1 and named it Puccinia NPR1 interactor (PNPi). PNPi interacts with the NPR1/NIM1-like domain of NPR1 via its C-terminal DPBB_1 domain. Using bimolecular fluorescence complementation assays, we detected the interaction between PNPi and wheat NPR1 in the nucleus of Nicotiana benthamiana protoplasts. A yeast three-hybrid assay showed that PNPi interaction with NPR1 competes with the interaction between wheat NPR1 and TGA2.2. In barley transgenic lines over expressing PNPi, we observed reduced induction of multiple PR genes in the region adjacent to Pseudomonas syringae pv. tomato DC3000 infection. Based on these results, we hypothesize that PNPi has a role in manipulating wheat defense response via its interactions with NPR1.
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Scientific Reports: CRISPR/Cas9-Mediated Immunity to Geminiviruses: Differential Interference and Evasion (2016)

Scientific Reports: CRISPR/Cas9-Mediated Immunity to Geminiviruses: Differential Interference and Evasion (2016) | Cereal and Biotrophic Pathogens | Scoop.it

The CRISPR/Cas9 system has recently been used to confer molecular immunity against several eukaryotic viruses, including plant DNA geminiviruses. Here, we provide a detailed analysis of the efficiencies of targeting different coding and non-coding sequences in the genomes of multiple geminiviruses. Moreover, we analyze the ability of geminiviruses to evade the CRISPR/Cas9 machinery. Our results demonstrate that the CRISPR/Cas9 machinery can efficiently target coding and non-coding sequences and interfere with various geminiviruses. Furthermore, targeting the coding sequences of different geminiviruses resulted in the generation of viral variants capable of replication and systemic movement. By contrast, targeting the noncoding intergenic region sequences of geminiviruses resulted in interference, but with inefficient recovery of mutated viral variants, which thus limited the generation of variants capable of replication and movement. Taken together, our results indicate that targeting noncoding, intergenic sequences provides viral interference activity and significantly limits the generation of viral variants capable of replication and systemic infection, which is essential for developing durable resistance strategies for long-term virus control.


Via Kamoun Lab @ TSL
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Regulation of sugar transporter activity for antibacterial defense in Arabidopsis

Regulation of sugar transporter activity for antibacterial defense in Arabidopsis | Cereal and Biotrophic Pathogens | Scoop.it
Microbial pathogens strategically acquire metabolites from their hosts during infection. Here we show that the host can intervene to prevent such metabolite loss to pathogens. Phosphorylation-dependent regulation of sugar transporter 13 (STP13) is required for antibacterial defense in the plant Arabidopsis thaliana . STP13 physically associates with the flagellin receptor flagellin-sensitive 2 (FLS2) and its co-receptor BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 (BAK1). BAK1 phosphorylates STP13 at threonine 485, which enhances its monosaccharide uptake activity to compete with bacteria for extracellular sugars. Limiting the availability of extracellular sugar deprives bacteria of an energy source and restricts virulence factor delivery. Our results reveal that control of sugar uptake, managed by regulation of a host sugar transporter, is a defense strategy deployed against microbial infection. Competition for sugar thus shapes host-pathogen interactions.

Via Tatsuya Nobori, Francis Martin
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Infection assays in Arabidopsis reveal candidate effectors from the poplar rust fungus that promote susceptibility to bacteria and oomycete pathogens - Germain - 2016 - Molecular Plant Pathology - ...

Infection assays in Arabidopsis reveal candidate effectors from the poplar rust fungus that promote susceptibility to bacteria and oomycete pathogens - Germain - 2016 - Molecular Plant Pathology - ... | Cereal and Biotrophic Pathogens | Scoop.it

Fungi of the Pucciniales order cause rust diseases, which altogether affect thousands of plant species worldwide and pose major threat to several crops. How rust effectors - virulence proteins delivered into infected tissues to modulate host functions - contribute to pathogen virulence remains poorly understood. Melampsora larici-populina is a devastating and widespread rust pathogen of poplars and its genome encodes 1,184 identified small secreted proteins that could potentially act as effectors. Here, following specific criteria we selected 16 candidate effector proteins and characterized their virulence activities and subcellular localizations in the leaf cells of Arabidopsis thaliana. Infection assays using bacterial (Pseudomonas syringae) and oomycete (Hyaloperonospora arabidopsidis) pathogens revealed subsets of candidate effectors that enhanced or decreased pathogen leaf colonization. Confocal imaging of GFP-tagged candidate effectors constitutively expressed in stable transgenic plants revealed that some protein fusions specifically accumulate in nuclei, chloroplasts, plasmodesmata and punctate cytosolic structures. Altogether, our analysis suggests that rust fungal candidate effectors target distinct cellular components in host cells to promote parasitic growth. 


Via Steve Marek
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AtCDC48A is involved in the turnover of an NLR immune receptor - Copeland - 2016 - The Plant Journal -

AtCDC48A is involved in the turnover of an NLR immune receptor - Copeland - 2016 - The Plant Journal - | Cereal and Biotrophic Pathogens | Scoop.it
Plants rely on different immune receptors to recognize pathogens and defend against pathogen attacks. Nucleotide-binding domain and leucine-rich repeat (NLR) proteins play a major role as intracellular immune receptors. Their homeostasis must be maintained at optimal levels in order to effectively recognize pathogens without causing autoimmunity. Previous studies have shown that the activity of the ubiquitin-proteasome system is essential to prevent excessive accumulation of NLR proteins such as Suppressor of NPR1, Constitutive 1 (SNC1). Attenuation of the ubiquitin E3 ligase SCFCPR1 (Constitutive expressor of Pathogenesis Related genes 1) or the E4 protein MUSE3 (Mutant, SNC1-Enhancing 3) leads to NLR accumulation and autoimmunity. In the current study, we report the identification of AtCDC48A as a negative regulator of NLR-mediated immunity. Plants carrying Atcdc48A-4, a partial loss-of-function allele of AtCDC48A, exhibit dwarf morphology and enhanced disease resistance to the oomycete pathogen Hyaloperonospora arabidopsidis (H.a.) Noco2. The SNC1 level is increased in Atcdc48A-4 plants and AtCDC48A interacts with MUSE3 in co-immunoprecipitation experiments, supporting a role for AtCDC48A in NLR turnover. While Arabidopsis contains four other paralogs of AtCDC48A, knockout mutants of these genes do not show obvious immunity-related phenotypes, suggesting functional divergence within this family. As an AAA-ATPase, AtCDC48A likely serves to process the poly-ubiquitinated NLR substrate for final protein degradation by the 26S proteasome.

Via Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant pathogens and pests
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Nature: Bacteria establish an aqueous living space in plants crucial for virulence (2016)

Nature: Bacteria establish an aqueous living space in plants crucial for virulence (2016) | Cereal and Biotrophic Pathogens | Scoop.it

High humidity has a strong influence on the development of numerous diseases affecting the above-ground parts of plants (the phyllosphere) in crop fields and natural ecosystems, but the molecular basis of this humidity effect is not understood. Previous studies have emphasized immune suppression as a key step in bacterial pathogenesis. Here we show that humidity-dependent, pathogen-driven establishment of an aqueous intercellular space (apoplast) is another important step in bacterial infection of the phyllosphere. Bacterial effectors, such as Pseudomonas syringae HopM1, induce establishment of the aqueous apoplast and are sufficient to transform non-pathogenic P. syringae strains into virulent pathogens in immunodeficient Arabidopsis thaliana under high humidity. Arabidopsis quadruple mutants simultaneously defective in a host target (AtMIN7) of HopM1 and in pattern-triggered immunity could not only be used to reconstitute the basic features of bacterial infection, but also exhibited humidity-dependent dyshomeostasis of the endophytic commensal bacterial community in the phyllosphere. These results highlight a new conceptual framework for understanding diverse phyllosphere–bacterial interactions.


Via Kamoun Lab @ TSL, Christophe Jacquet
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Rescooped by Xiaodong Wang from Plant pathogens and pests
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Plant science: A war over water when bacteria invade leaves : Nature : Nature Research

Plant science: A war over water when bacteria invade leaves : Nature : Nature Research | Cereal and Biotrophic Pathogens | Scoop.it
Invading bacterial leaf pathogens disarm a plant's defence mechanisms by injecting what are known as effector proteins directly into plant cells. In addition to the plant's defence mechanisms, invading bacteria might encounter another obstacle — a severe shortage of water in the leaf intercellular space (apoplast) that limits bacterial growth. On page 524, Xin et al.1 report that Pseudomonas syringae bacteria inject effector proteins that specifically target plant-cell processes to promote apoplast hydration, thereby creating an environment suitable for bacterial growth.

Via Christophe Jacquet
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