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Plant-microbe interaction
Current research on plant immunity, effector proteins, and other inspiring articles
Curated by Suayib Üstün
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Plant Cell: Colletotrichum orbiculare Secretes Virulence Effectors to a Biotrophic Interface at the Primary Hyphal Neck via Exocytosis Coupled with SEC22-Mediated Traffic (2014)

Plant Cell: Colletotrichum orbiculare Secretes Virulence Effectors to a Biotrophic Interface at the Primary Hyphal Neck via Exocytosis Coupled with SEC22-Mediated Traffic (2014) | Plant-microbe interaction | Scoop.it

The hemibiotrophic pathogen Colletotrichum orbiculare develops biotrophic hyphae inside cucumber (Cucumis sativus) cells via appressorial penetration; later, the pathogen switches to necrotrophy. C. orbiculare also expresses specific effectors at different stages. Here, we found that virulence-related effectors of C. orbiculare accumulate in a pathogen–host biotrophic interface. Fluorescence-tagged effectors accumulated in a ring-like region around the neck of the biotrophic primary hyphae. Fluorescence imaging of cellular components and transmission electron microscopy showed that the ring-like signals of the effectors localized at the pathogen–plant interface. Effector accumulation at the interface required induction of its expression during the early biotrophic phase, suggesting that transcriptional regulation may link to effector localization. We also investigated the route of effector secretion to the interface. An exocytosis-related component, the Rab GTPase SEC4, localized to the necks of biotrophic primary hyphae adjacent to the interface, thereby suggesting focal effector secretion. Disruption of SEC4 in C. orbiculare reduced virulence and impaired effector delivery to the ring signal interface. Disruption of the v-SNARE SEC22also reduced effector delivery. These findings suggest that biotrophy-expressed effectors are secreted, via the endoplasmic reticulum-to-Golgi route and subsequent exocytosis, toward the interface generated between C. orbiculare and the host cell.


Via Kamoun Lab @ TSL, Jim Alfano
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Effector MiSSP7 of the mutualistic fungus Laccaria bicolor stabilizes the Populus JAZ6 protein and represses jasmonic acid (JA) responsive genes

Effector MiSSP7 of the mutualistic fungus Laccaria bicolor stabilizes the Populus JAZ6 protein and represses jasmonic acid (JA) responsive genes | Plant-microbe interaction | Scoop.it

Ectomycorrhizal fungi, such as Laccaria bicolor, support forest growth and sustainability by providing growth-limiting nutrients to their plant host through a mutualistic symbiotic relationship with host roots. We have previously shown that the effector protein MiSSP7 (Mycorrhiza-induced Small Secreted Protein 7) encoded by L. bicolor is necessary for the establishment of symbiosis with host trees, although the mechanistic reasoning behind this role was unknown. We demonstrate here that MiSSP7 interacts with the host protein PtJAZ6, a negative regulator of jasmonic acid (JA)-induced gene regulation in Populus. As with other characterized JASMONATE ZIM-DOMAIN (JAZ) proteins, PtJAZ6 interacts with PtCOI1 in the presence of the JA mimic coronatine, and PtJAZ6 is degraded in plant tissues after JA treatment. The association between MiSSP7 and PtJAZ6 is able to protect PtJAZ6 from this JA-induced degradation. Furthermore, MiSSP7 is able to block—or mitigate—the impact of JA on L. bicolor colonization of host roots. We show that the loss of MiSSP7 production by L. bicolor can be complemented by transgenically varying the transcription of PtJAZ6 or through inhibition of JA-induced gene regulation. We conclude that L. bicolor, in contrast to arbuscular mycorrhizal fungi and biotrophic pathogens, promotes mutualism by blocking JA action through the interaction of MiSSP7 with PtJAZ6.

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PhD Position in Plant-Pathogen Interaction available in our Lab

PhD Position in Plant-Pathogen Interaction available in our Lab | Plant-microbe interaction | Scoop.it
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Stitching together the Multiple Dimensions of Autophagy Using Metabolomics and Transcriptomics Reveals Impacts on Metabolism, Development, and Plant Responses to the Environment in Arabidopsis

Stitching together the Multiple Dimensions of Autophagy Using Metabolomics and Transcriptomics Reveals Impacts on Metabolism, Development, and Plant Responses to the Environment in Arabidopsis | Plant-microbe interaction | Scoop.it

Autophagy is a fundamental process in the plant life story, playing a key role in immunity, senescence, nutrient recycling, and adaptation to the environment. Transcriptomics and metabolomics of the rosette leaves of Arabidopsis thaliana autophagy mutants (atg) show that autophagy is essential for cell homeostasis and stress responses and that several metabolic pathways are affected. Depletion of hexoses, quercetins, and anthocyanins parallel the overaccumulation of several amino acids and related compounds, such as glutamate, methionine, glutathione, pipecolate, and 2-aminoadipate. Transcriptomic data show that the pathways for glutathione, methionine, raffinose, galacturonate, and anthocyanin are perturbed. Anthocyanin depletion in atg mutants, which was previously reported as a possible defect in flavonoid trafficking to the vacuole, appears due to the downregulation of the master genes encoding the enzymes and regulatory proteins involved in flavonoid biosynthesis. Overexpression of the PRODUCTION OF ANTHOCYANIN PIGMENT1 transcription factor restores anthocyanin accumulation in vacuoles of atg mutants. Transcriptome analyses reveal connections between autophagy and (1) salicylic acid biosynthesis and response, (2) cytokinin perception, (3) oxidative stress and plant defense, and possible interactions between autophagy and the COP9 signalosome machinery. The metabolic and transcriptomic signatures identified for the autophagy mutants are discussed and show consistencies with the observed phenotypes.

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BMC Genomics | Abstract | Secretome analysis reveals effector candidates associated with broad host range necrotrophy in the fungal plant pathogen Sclerotinia sclerotiorum

BMC Genomics | Abstract | Secretome analysis reveals effector candidates associated with broad host range necrotrophy in the fungal plant pathogen Sclerotinia sclerotiorum | Plant-microbe interaction | Scoop.it
Background

The white mold fungus Sclerotinia sclerotiorum is a devastating necrotrophic plant pathogen with a remarkably broad host range. The interaction of necrotrophs with their hosts is more complex than initially thought, and still poorly understood.

Results

We combined bioinformatics approaches to determine the repertoire of S. sclerotiorum effector candidates and conducted detailed sequence and expression analyses on selected candidates. We identified 486 S. sclerotiorum secreted protein genes expressed in planta, many of which have no predicted enzymatic activity and may be involved in the interaction between the fungus and its hosts. We focused on those showing (i) protein domains and motifs found in known fungal effectors, (ii) signatures of positive selection, (iii) recent gene duplication, or (iv) being S. sclerotiorum-specific. We identified 78 effector candidates based on these properties. We analyzed the expression pattern of 16 representative effector candidate genes on four host plants and revealed diverse expression patterns.

Conclusions

These results reveal diverse predicted functions and expression patterns in the repertoire of S. sclerotiorum effector candidates. They will facilitate the functional analysis of fungal pathogenicity determinants and should prove useful in the search for plant quantitative disease resistance components active against the white mold.

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An XA21-Associated Kinase (OsSERK2) Regulates Immunity Mediated by the XA21 and XA3 Immune Receptors

An XA21-Associated Kinase (OsSERK2) Regulates Immunity Mediated by the XA21 and XA3 Immune Receptors | Plant-microbe interaction | Scoop.it

The rice XA21 immune receptor kinase and the structurally related XA3 receptor confer immunity to Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial leaf blight. Here we report the isolation of OsSERK2 (rice somatic embryogenesis receptor kinase 2) and demonstrate that OsSERK2 positively regulates immunity mediated by XA21 and XA3 as well as the rice immune receptor FLS2 (OsFLS2). Rice plants silenced forOsSerk2 display altered morphology and reduced sensitivity to the hormone brassinolide. OsSERK2 interacts with the intracellular domains of each immune receptor in the yeast two-hybrid system in a kinase activity-dependent manner. OsSERK2 undergoes bidirectional transphosphorylation with XA21 in vitro and forms a constitutive complex with XA21 in vivo. These results demonstrate an essential role for OsSERK2 in the function of three rice immune receptors and suggest that direct interaction with the rice immune receptors is critical for their function. Taken together, our findings suggest that the mechanism of OsSERK2-meditated regulation of rice XA21, XA3, and FLS2 differs from that of AtSERK3/BAK1-mediated regulation of Arabidopsis FLS2 and EFR.

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The H+-ATPase HA1 of Medicago truncatula Is Essential for Phosphate Transport and Plant Growth during Arbuscular Mycorrhizal Symbiosis

The H+-ATPase HA1 of Medicago truncatula Is Essential for Phosphate Transport and Plant Growth during Arbuscular Mycorrhizal Symbiosis | Plant-microbe interaction | Scoop.it

A key feature of arbuscular mycorrhizal symbiosis is improved phosphorus nutrition of the host plant via the mycorrhizal pathway, i.e., the fungal uptake of Pi from the soil and its release from arbuscules within root cells. Efficient transport of Pi from the fungus to plant cells is thought to require a proton gradient across the periarbuscular membrane (PAM) that separates fungal arbuscules from the host cell cytoplasm. Previous studies showed that the H+-ATPase gene HA1 is expressed specifically in arbuscule-containing root cells of Medicago truncatula. We isolated a ha1-2 mutant of M. truncatula and found it to be impaired in the development of arbuscules but not in root colonization by Rhizophagus irregularis hyphae. Artificial microRNA silencing of HA1 recapitulated this phenotype, resulting in small and truncated arbuscules. Unlike the wild type, the ha1-2 mutant failed to show a positive growth response to mycorrhizal colonization under Pi-limiting conditions. Uptake experiments confirmed that ha1-2 mutants are unable to take up phosphate via the mycorrhizal pathway. Increased pH in the apoplast of abnormal arbuscule-containing cells of the ha1-2 mutant compared with the wild type suggests that HA1 is crucial for building a proton gradient across the PAM and therefore is indispensible for the transfer of Pi from the fungus to the plant.

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Inside plant: biotrophic strategies to modulate host immunity and metabolism

Inside plant: biotrophic strategies to modulate host immunity and metabolism | Plant-microbe interaction | Scoop.it

Filamentous plant pathogens that establish biotrophic interactions need to avoid plant immune responses. Recent findings from different pathosystems suggest that sufficient suppression of host immunity is based on the modulation of a rather limited number of host targets. Microbial strategies to target host physiology dependent on the duration of biotrophy, the style of host tissue colonization and the degree of interference with plant development. In this article, we present current concepts in biotrophic virulence strategies and discuss mechanisms of pathogen adaptation and effector specialization.

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Contrasting roles of apoplastic aspartyl protease AED1 and legume lectin-like protein LLP1 in Arabidopsis systemic acquired resistance

Systemic acquired resistance (SAR) is an inducible immune response that depends on ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1). Here, we show that Arabidopsis thaliana EDS1 is required for both SAR signal generation in primary infected leaves and SAR signal perception in systemic uninfected tissues. In contrast to SAR signal generation, local resistance remains intact in eds1 mutant plants in response to Pseudomonas syringae delivering the effector protein AvrRpm1. We utilized the SAR-specific phenotype of the eds1 mutant to identify new SAR regulatory proteins in plants conditionally expressing AvrRpm1. Comparative proteomic analysis of apoplast-enriched extracts from AvrRpm1-expressing wild type and eds1 mutant plants led to the identification of 12 APOPLASTIC, EDS1-DEPENDENT (AED) proteins. The genes encoding AED1, a predicted aspartyl protease, and another AED, LEGUME LECTIN-LIKE PROTEIN1 (LLP1), were induced locally and systemically during SAR signaling and locally by salicylic acid (SA) or its functional analog BTH. Because conditional over-accumulation of AED1-HA inhibited SA-induced resistance and SAR but not local resistance, the data suggest that AED1 is part of a homeostatic feedback mechanism regulating systemic immunity. In llp1 mutant plants, SAR was compromised, whereas the local resistance that is normally associated with EDS1 and SA as well as responses to exogenous SA appeared largely unaffected. Together, the data indicate that LLP1 promotes systemic rather than local immunity, possibly in parallel with SA. Our analysis reveals new positive and negative components of SAR and reinforces the notion that SAR represents a distinct phase of plant immunity beyond local resistance.

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Noncanonical Role for the Host Vps4 AAA+ ATPase ESCRT Protein in the Formation of Tomato Bushy Stunt Virus Replicase

Noncanonical Role for the Host Vps4 AAA+ ATPase ESCRT Protein in the Formation of Tomato Bushy Stunt Virus Replicase | Plant-microbe interaction | Scoop.it

Assembling of the membrane-bound viral replicase complexes (VRCs) consisting of viral- and host-encoded proteins is a key step during the replication of positive-stranded RNA viruses in the infected cells. Previous genome-wide screens with Tomato bushy stunt tombusvirus (TBSV) in a yeast model host have revealed the involvement of eleven cellular ESCRT (endosomal sorting complexes required for transport) proteins in viral replication. The ESCRT proteins are involved in endosomal sorting of cellular membrane proteins by forming multiprotein complexes, deforming membranes away from the cytosol and, ultimately, pinching off vesicles into the lumen of the endosomes. In this paper, we show an unexpected key role for the conserved Vps4p AAA+ ATPase, whose canonical function is to disassemble the ESCRT complexes and recycle them from the membranes back to the cytosol. We find that the tombusvirus p33 replication protein interacts with Vps4p and three ESCRT-III proteins. Interestingly, Vps4p is recruited to become a permanent component of the VRCs as shown by co-purification assays and immuno-EM. Vps4p is co-localized with the viral dsRNA and contacts the viral (+)RNA in the intracellular membrane. Deletion of Vps4p in yeast leads to the formation of crescent-like membrane structures instead of the characteristic spherule and vesicle-like structures. The in vitro assembled tombusvirus replicase based on cell-free extracts (CFE) from vps4Δ yeast is highly nuclease sensitive, in contrast with the nuclease insensitive replicase in wt CFE. These data suggest that the role of Vps4p and the ESCRT machinery is to aid building the membrane-bound VRCs, which become nuclease-insensitive to avoid the recognition by the host antiviral surveillance system and the destruction of the viral RNA. Other (+)RNA viruses of plants and animals might also subvert Vps4p and the ESCRT machinery for formation of VRCs, which require membrane deformation and spherule formation.

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The Arabidopsis thaliana mitogen-activated protein kinases MPK3 and MPK6 target a subclass of ‘VQ-motif’-containing proteins to regulate immune responses - Pecher - 2014 - New Phytologist - Wiley O...

The Arabidopsis thaliana mitogen-activated protein kinases MPK3 and MPK6 target a subclass of ‘VQ-motif’-containing proteins to regulate immune responses - Pecher - 2014 - New Phytologist - Wiley O... | Plant-microbe interaction | Scoop.it
SummaryMitogen-activated protein kinase (MAPK) cascades play key roles in plant immune signalling, and elucidating their regulatory functions requires the identification of the pathway-specific substrates.We used yeast two-hybrid interaction screens, in vitro kinase assays and mass spectrometry-based phosphosite mapping to study a family of MAPK substrates. Site-directed mutagenesis and promoter-reporter fusion studies were performed to evaluate the impact of substrate phosphorylation on downstream signalling.A subset of the Arabidopsis thaliana VQ-motif-containing proteins (VQPs) were phosphorylated by the MAPKs MPK3 and MPK6, and renamed MPK3/6-targeted VQPs (MVQs). When plant protoplasts (expressing these MVQs) were treated with the flagellin-derived peptide flg22, several MVQs were destabilized in vivo. The MVQs interact with specific WRKY transcription factors. Detailed analysis of a representative member of the MVQ subset, MVQ1, indicated a negative role in WRKY-mediated defence gene expression – with mutation of the VQ-motif abrogating WRKY binding and causing mis-regulation of defence gene expression.We postulate the existence of a variety of WRKY-VQP-containing transcriptional regulatory protein complexes that depend on spatio-temporal VQP and WRKY expression patterns. Defence gene transcription can be modulated by changing the composition of these complexes – in part – through MAPK-mediated VQP degradation.
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Science: Structural Basis for Assembly and Function of a Heterodimeric Plant Immune Receptor (2014)

Science: Structural Basis for Assembly and Function of a Heterodimeric Plant Immune Receptor (2014) | Plant-microbe interaction | Scoop.it

Cytoplasmic plant immune receptors recognize specific pathogen effector proteins and initiate effector-triggered immunity. In Arabidopsis, the immune receptors RPS4 and RRS1 are both required to activate defense to three different pathogens. We show that RPS4 and RRS1 physically associate. Crystal structures of the N-terminal Toll–interleukin-1 receptor/resistance (TIR) domains of RPS4 and RRS1, individually and as a heterodimeric complex (respectively at 2.05, 1.75, and 2.65 angstrom resolution), reveal a conserved TIR/TIR interaction interface. We show that TIR domain heterodimerization is required to form a functional RRS1/RPS4 effector recognition complex. The RPS4 TIR domain activates effector-independent defense, which is inhibited by the RRS1 TIR domain through the heterodimerization interface. Thus, RPS4 and RRS1 function as a receptor complex in which the two components play distinct roles in recognition and signaling.


See also Perspective by Nishimura and Dangl http://www.sciencemag.org/content/344/6181/267.short


Via Kamoun Lab @ TSL
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The Endophytic Strain Rhizobium sp. AP16 Produces the Proteasome Inhibitor Syringolin A

Syringolin A, the product of a mixed non-ribosomal peptide synthetase/polyketide synthase encoded by the syl gene cluster, is a virulence factor secreted by certain Pseudomonas syringae strains. Together with the glidobactins produced by a number of β- and γ-proteobacterial human and animal pathogens, it belongs to the syrbactins, a structurally novel class of proteasome inhibitors. In plants, proteasome inhibition by syringolin A-producing P. syringae strains leads to the suppression of host defense pathways requiring proteasome activity, such as the ones mediated by salicylic acid and jasmonic acid. Here we report the discovery of a syl-like gene cluster with some unusual features in the α-proteobacterial endophyte Rhizobium sp. AP16 that encodes a putative syringolin A-like synthetase whose components share 55-65% sequence identity (72-79% similarity) at the amino acid level. As revealed by ANI (average nucleotide identity) calculation, this strain likely belongs to the same species as the biocontrol strain R. rhizogenes K84 (formely known as Agrobacterium radiobacter K84), which, however, carries a non-functional deletion remnant of the syl-like gene cluster. Here we present a functional analysis of the syl-like gene cluster of Rhizobium sp. AP16 and demonstrate that this endophyte synthesizes syringolin A and some related minor variants, suggesting that proteasome inhibition by syrbactin production not only can be important for pathogens but also for endophytic bacteria in the interaction with their hosts.

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MPMI: P. syringae CC1557: a highly virulent strain with an unusually small type III effector repertoire that includes a novel effector (2014)

MPMI: P. syringae CC1557: a highly virulent strain with an unusually small type III effector repertoire that includes a novel effector (2014) | Plant-microbe interaction | Scoop.it

Both type III effector proteins and non-ribosomal peptide toxins play important roles for Pseudomonas syringae pathogenicity in host plants, but whether and how these pathways interact to promote infection remains unclear. Genomic evidence from one clade of P. syringae suggests a tradeoff between the total number of type III effector proteins and presence of syringomycin, syringopeptin, and syringolin A toxins. Here we report the complete genome sequence from P. syringae CC1557, which contains the lowest number of known type III effectors to date and has also acquired genes similar to sequences encoding syringomycin pathways from other strains. We demonstrate that this strain is pathogenic on Nicotiana benthamiana and that both the type III secretion system and a new type III effector family, hopBJ1, contribute to pathogenicity. We further demonstrate that activity of HopBJ1 is dependent on residues structurally similar to the catalytic site of E. coli CNF1 toxin. Taken together, our results provide additional support for a negative correlation between type III effector repertoires and the potential to produce syringomycin-like toxins while also highlighting how genomic synteny and bioinformatics can be used to identify and characterize novel virulence proteins.


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Border Control—A Membrane-Linked Interactome of Arabidopsis

Border Control—A Membrane-Linked Interactome of Arabidopsis | Plant-microbe interaction | Scoop.it

Cellular membranes act as signaling platforms and control solute transport. Membrane receptors, transporters, and enzymes communicate with intracellular processes through protein-protein interactions. Using a split-ubiquitin yeast two-hybrid screen that covers a test-space of 6.4 × 106 pairs, we identified 12,102 membrane/signaling protein interactions from Arabidopsis. Besides confirmation of expected interactions such as heterotrimeric G protein subunit interactions and aquaporin oligomerization, >99% of the interactions were previously unknown. Interactions were confirmed at a rate of 32% in orthogonal in planta split–green flourescent protein interaction assays, which was statistically indistinguishable from the confirmation rate for known interactions collected from literature (38%). Regulatory associations in membrane protein trafficking, turnover, and phosphorylation include regulation of potassium channel activity through abscisic acid signaling, transporter activity by a WNK kinase, and a brassinolide receptor kinase by trafficking-related proteins. These examples underscore the utility of the membrane/signaling protein interaction network for gene discovery and hypothesis generation in plants and other organisms.

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Biswapriya Biswavas Misra's curator insight, June 4, 7:56 PM

Cellular membranes act as signaling platforms and control solute transport. Membrane receptors, transporters, and enzymes communicate with intracellular processes through protein-protein interactions. Using a split-ubiquitin yeast two-hybrid screen that covers a test-space of 6.4 × 106 pairs, we identified 12,102 membrane/signaling protein interactions from Arabidopsis. Besides confirmation of expected interactions such as heterotrimeric G protein subunit interactions and aquaporin oligomerization, >99% of the interactions were previously unknown. Interactions were confirmed at a rate of 32% in orthogonal in planta split–green flourescent protein interaction assays, which was statistically indistinguishable from the confirmation rate for known interactions collected from literature (38%). Regulatory associations in membrane protein trafficking, turnover, and phosphorylation include regulation of potassium channel activity through abscisic acid signaling, transporter activity by a WNK kinase, and a brassinolide receptor kinase by trafficking-related proteins. These examples underscore the utility of the membrane/signaling protein interaction network for gene discovery and hypothesis generation in plants and other organisms.

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Frontiers | Role of NPR1 and KYP in long-lasting induced resistance by β-aminobutyric acid | Plant Physiology

Frontiers | Role of NPR1 and KYP in long-lasting induced resistance by β-aminobutyric acid | Plant Physiology | Plant-microbe interaction | Scoop.it
Priming of defence increases the responsiveness of the plant immune system and can provide broad-spectrum protection against disease. Recent evidence suggests that priming of defence can be inherited epigenetically to following generations. However, the mechanisms of long-lasting defence priming within one generation remains poorly understood. Here, we have investigated the mechanistic basis of long-lasting induced resistance after treatment with ß-amino butyric acid (BABA), an agent that mimics biologically induced resistance phenomena. BABA-induced resistance is based on priming of salicylic acid (SA)-dependent and SA–independent defences. BABA-induced resistance could be detected up to 28 days after treatment of wild-type Arabidopsis. This long-lasting component of the induced resistance response requires the regulatory protein NPR1 and is associated with priming of SA-inducible genes. In contrast, NPR1-independent resistance by BABA was transient and had disappeared by 14 days after treatment. Chromatin immunoprecipitation (ChIP) assays revealed no increased acetylation of histone H3K9 at promoters regions of priming-responsive genes, indicating that this post-translational histone modification is not critical for long-term transcriptional priming. Interestingly, the kyp-6 mutant, which is affected in methyltransferase activity of H3K9, was blocked in long-lasting BABA-induced resistance, indicating a critical requirement of this post-translational histone modification in long-lasting BABA-IR. Considering that KYP suppresses gene transcription through methylation of H3K9 and CpHpG DNA methylation, we propose that KYP enables long-term defence gene priming by silencing suppressor genes of SA/NPR1-dependent genes.
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Plant Physiology: The plant membrane-associated REM1.3 remorin accumulates in discrete perihaustorial domains and enhances susceptibility to Phytophthora infestans (2014)

Plant Physiology: The plant membrane-associated REM1.3 remorin accumulates in discrete perihaustorial domains and enhances susceptibility to Phytophthora infestans (2014) | Plant-microbe interaction | Scoop.it

Filamentous pathogens such as the oomycete Phytophthora infestans infect plants by developing specialized structures termed haustoria inside the host cells. Haustoria are thought to enable secretion of effector proteins into the plant cells. Haustorium biogenesis is therefore critical for pathogen accommodation in the host tissue. Haustoria are enveloped by a specialized host-derived membrane, the extrahaustorial membrane (EHM), which is distinct from the plant plasma membrane. The mechanisms underlying the biogenesis of the EHM are unknown. Remarkably, several plasma membrane localised proteins are excluded from the EHM but the remorin REM1.3 accumulates around P. infestans haustoria. Here, we used overexpression, co-localization with reporter proteins, and super-resolution microscopy in cells infected by P. infestans to reveal discrete EHM domains labelled by REM1.3 and P. infestans effector AVRblb2. Moreover, SYT1 synaptotagmin, another previously identified perihaustorial protein, localized to subdomains which are mainly not labelled by REM1.3 and AVRblb2. Functional characterization of REM1.3 revealed that it is a susceptibility factor that promotes infection by P. infestans. This activity, and REM1.3 recruitment to the EHM, require REM1.3 membrane binding domain. Our results implicate REM1.3 membrane micro-domains in plant susceptibility to an oomycete pathogen.


Via Kamoun Lab @ TSL
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Jean-Michel Ané's curator insight, May 14, 1:17 PM

I know that it is not a symbiont but... some people will guess why I am scooping this :-)

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Salmonella enterica induces and subverts the plant immune system

Salmonella enterica induces and subverts the plant immune system | Plant-microbe interaction | Scoop.it

Scooped from: Frontiers in Microbiology, 2014

Authors: Ana V. García and Heribert Hirt

 

Summary:

Infections with Salmonella enterica belong to the most prominent causes of food poisoning and infected fruits and vegetables represent important vectors for salmonellosis. Whereas it was shown that plants raise defense responses against Salmonella, these bacteria persist and proliferate in various plant tissues. Recent reports shed light into the molecular interaction between plants and Salmonella, highlighting the defense pathways induced and the means used by the bacteria to escape the plant immune system and accomplish colonization. It was recently shown that plants detect Salmonella pathogen-associated molecular patterns (PAMPs), such as the flagellin peptide flg22, and activate hallmarks of the defense program known as PAMP-triggered immunity (PTI). Interestingly, certain Salmonella strains carry mutations in the flg22 domain triggering PTI, suggesting that a strategy of Salmonella is to escape plant detection by mutating PAMP motifs. Another strategy may rely on the type III secretion system (T3SS) as T3SS mutants were found to induce stronger plant defense responses than wild type bacteria. Although Salmonella effector delivery into plant cells has not been shown, expression of Salmonella effectors in plant tissues shows that these bacteria also possess powerful means to manipulate the plant immune system. Altogether, the data gathered suggest that Salmonella triggers PTI in plants and evolved strategies to avoid or subvert plant immunity.


Via Freddy Monteiro, Jean-Michel Ané, Mary Williams
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Freddy Monteiro's curator insight, April 29, 4:22 PM

Provocative....

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A Potential Disease Susceptibility Gene CsLOB of Citrus Is Targeted by a Major Virulence Effector PthA of Xanthomonas citri subsp. citri

A Potential Disease Susceptibility Gene CsLOB of Citrus Is Targeted by a Major Virulence Effector PthA of Xanthomonas citri subsp. citri | Plant-microbe interaction | Scoop.it
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Plant perception of β-aminobutyric acid is mediated by an aspartyl-tRNA synthetase : Nature Chemical Biology : Nature Publishing Group

Plant perception of β-aminobutyric acid is mediated by an aspartyl-tRNA synthetase : Nature Chemical Biology : Nature Publishing Group | Plant-microbe interaction | Scoop.it

Specific chemicals can prime the plant immune system for augmented defense. β-aminobutyric acid (BABA) is a priming agent that provides broad-spectrum disease protection. However, BABA also suppresses plant growth when applied in high doses, which has hampered its application as a crop defense activator. Here we describe a mutant of Arabidopsis thaliana that is impaired in BABA-induced disease immunity (ibi1) but is hypersensitive to BABA-induced growth repression. IBI1 encodes an aspartyl-tRNA synthetase. Enantiomer-specific binding of the R enantiomer of BABA to IBI1 primed the protein for noncanonical defense signaling in the cytoplasm after pathogen attack. This priming was associated with aspartic acid accumulation and tRNA-induced phosphorylation of translation initiation factor eIF2α. However, mutation of eIF2α-phosphorylating GCN2 kinase did not affect BABA-induced immunity but relieved BABA-induced growth repression. Hence, BABA-activated IBI1 controls plant immunity and growth via separate pathways. Our results open new opportunities to separate broad-spectrum disease resistance from the associated costs on plant growth.

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

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

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

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Functionally Redundant RXLR Effectors from Phytophthora infestans Act at Different Steps to Suppress Early flg22-Triggered Immunity

Functionally Redundant RXLR Effectors from Phytophthora infestans Act at Different Steps to Suppress Early flg22-Triggered Immunity | Plant-microbe interaction | Scoop.it

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

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Clathrin and Membrane Microdomains Cooperatively Regulate RbohD Dynamics and Activity in Arabidopsis

Clathrin and Membrane Microdomains Cooperatively Regulate RbohD Dynamics and Activity in Arabidopsis | Plant-microbe interaction | Scoop.it

Arabidopsis thaliana respiratory burst oxidase homolog D (RbohD) functions as an essential regulator of reactive oxygen species (ROS). However, our understanding of the regulation of RbohD remains limited. By variable-angle total internal reflection fluorescence microscopy, we demonstrate that green fluorescent protein (GFP)-RbohD organizes into dynamic spots at the plasma membrane. These RbohD spots have heterogeneous diffusion coefficients and oligomerization states, as measured by photobleaching techniques. Stimulation with ionomycin and calyculin A, which activate the ROS-producing enzymatic activity of RbohD, increases the diffusion and oligomerization of RbohD. Abscisic acid and flg22 treatments also increase the diffusion coefficient and clustering of GFP-RbohD. Single-particle analysis in clathrin heavy chain2 mutants and a Flotillin1 artificial microRNA line demonstrated that clathrin- and microdomain-dependent endocytic pathways cooperatively regulate RbohD dynamics. Under salt stress, GFP-RbohD assembles into clusters and then internalizes into the cytoplasm. Dual-color fluorescence cross-correlation spectroscopy analysis further showed that salt stress stimulates RbohD endocytosis via membrane microdomains. We demonstrate that microdomain-associated RbohD spots diffuse at the membrane with high heterogeneity, and these dynamics closely relate to RbohD activity. Our results provide insight into the regulation of RbohD activity by clustering and endocytosis, which facilitate the activation of redox signaling pathways.

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Decreased abundance of type III secretion system-inducing signals in Arabidopsis mkp1 enhances resistance against Pseudomonas syringae

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

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

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Frontiers: Induced plant responses to microbes and insects

Frontiers: Induced plant responses to microbes and insects | Plant-microbe interaction | Scoop.it

Plants are members of complex communities and interact both with antagonists and beneficial organisms. An important question in plant defense-signaling research is how plants integrate signals induced by pathogens, insect herbivores and beneficial microbes into the most appropriate adaptive response. Molecular and genomic tools are now being used to uncover the complexity of the induced defense signaling networks that have evolved during the arms races between plants and the other organisms with which they intimately interact. To understand the functioning of the complex defense signaling network in nature, molecular biologists and ecologists have joined forces to place molecular mechanisms of induced plant defenses in an ecological perspective. In this Research Topic, we aim to provide an on-line, open-access snapshot of the current state of the art of the field of induced plant responses to microbes and insects, with a special focus on the translation of molecular mechanisms to ecology and vice versa. We will collect Original Research and Review papers on the topic, but also other article types, such as Methods and Opinions are welcome.

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Joseph Charlton's curator insight, April 16, 4:03 PM

Great collection of articles on the plants responses to microbes and insects!