Plant immunity and legume symbiosis
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Plant immunity and legume symbiosis
Dedicated to plant mechanisms involved in response to pathogens, pests or symbionts. This site is complementary to the Plant pathogens and pests scoop-it site  :        http://www.scoop.it/t/erbilate. The role of hormones involved in regulation of plant responses to microorganisms is also reported in the "Plant hormones " site at http://www.scoop.it/t/plant-hormones-by-christophe-jacquet .
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A resistosome-activated ‘death switch’

A resistosome-activated ‘death switch’ | Plant immunity and legume symbiosis | Scoop.it
Pathogen perception triggers a monomeric nucleotide-binding leucine-rich plant immune receptor to form a pentameric wheel-like complex termed a resistosome, with the N-terminal α helices forming a funnel-shaped structure that may perturb plasma membrane integrity to cause hypersensitive cell death.
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Plant Malectin-Like Receptor Kinases: From Cell Wall Integrity to Immunity and Beyond | Annual Review of Plant Biology

Plant Malectin-Like Receptor Kinases: From Cell Wall Integrity to Immunity and Beyond | Annual Review of Plant Biology | Plant immunity and legume symbiosis | Scoop.it
Plant cells are surrounded by cell walls protecting them from a myriad of environmental challenges. For successful habitat adaptation, extracellular cues are perceived at the cell wall and relayed to downstream signaling constituents to mediate dynamic cell wall remodeling and adapted intracellular responses. Plant malectin-like receptor kinases, also known as Catharanthus roseus receptor-like kinase 1-like proteins (CrRLK1Ls), take part in these perception and relay processes. CrRLK1Ls are involved in many different plant functions. Their ligands, interactors, and downstream signaling partners are being unraveled, and studies about CrRLK1Ls’ roles in plant species other than the plant model Arabidopsis thaliana are beginning to flourish. This review focuses on recent CrRLK1L-related advances in cell growth, reproduction, hormone signaling, abiotic stress responses, and, particularly, immunity. We also give an overview of the comparative genomics and evolution of CrRLK1Ls, and present a brief outlook for future research.
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A Plant Immune Receptor Adopts a Two-Step Recognition Mechanism to Enhance Viral Effector Perception - ScienceDirect

A Plant Immune Receptor Adopts a Two-Step Recognition Mechanism to Enhance Viral Effector Perception - ScienceDirect | Plant immunity and legume symbiosis | Scoop.it
Plant intracellular nucleotide binding leucine-rich repeat (NLR) immune receptors play critical roles in pathogen surveillance. Most plant NLRs characterized so far were found to use a single domain/sensor to recognize pathogen effectors. Here we report that the Sw-5b NLR immune receptor uses two distinct domains to detect the viral movement protein NSm encoded by tospovirus. In addition to its leucine-rich repeat (LRR) domain that has been previously reported, the N-terminal Solanaceae domain (SD) of Sw-5b also interacts with NSm and a conserved 21-amino-acid region of NSm (NSm21). The specific interaction between Sw-5b SD and NSm is required for releasing the inhibitory effect of coiled-coil domain on the NB-ARC-LRR region. Furthermore, we found that the binding of NSm affects the nucleotide binding activity of the NB-ARC-LRR in vitro, while Sw-5b NB-ARC-LRR is activated only when NSm and NSm21 levels are high. Interestingly, Sw-5b SD could significantly enhance the ability of the NB-ARC-LRR to detect low levels of NSm effector and facilitate its activation and induction of defense response. An Sw-5b SD mutant that is disrupted in NSm recognition failed to enhance the ability of the NB-ARC-LRR to sense low levels of NSm and NSm21. Taken together, our results suggest that Sw-5b SD functions as an extra sensor and the NB-ARC-LRR as an activator, and that Sw-5b NLR adopts a two-step recognition mechanism to enhance viral effector perception.
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The Cotton Apoplastic Protein CRR1 Stabilizes Chitinase 28 to Facilitate Defense against the Fungal Pathogen Verticillium dahliae

The Cotton Apoplastic Protein CRR1 Stabilizes Chitinase 28 to Facilitate Defense against the Fungal Pathogen Verticillium dahliae | Plant immunity and legume symbiosis | Scoop.it
The apoplast serves as the first battlefield between the plant hosts and invading microbes; therefore, work on plant-pathogen interactions has increasingly focused on apoplastic immunity. In this study, we identified three proteins in the apoplast of cotton (Gossypium sp) root cells during interaction of the plant with the fungal pathogen Verticillium dahliae. Among these proteins, cotton host cells secrete chitinase 28 (Chi28) and the Cys-rich repeat protein 1 (CRR1), while the pathogen releases the protease VdSSEP1. Biochemical analysis demonstrated that VdSSEP1 hydrolyzed Chi28, but CRR1 protected Chi28 from cleavage by Verticillium dahliae secretory Ser protease 1 (VdSSEP1). In accordance with the in vitro results, CRR1 interacted with Chi28 in yeast and plant cells and attenuated the observed decrease in Chi28 level that occurred in the apoplast of plant cells upon pathogen attack. Knockdown of CRR1 or Chi28 in cotton plants resulted in higher susceptibility to V. dahliae infection, and overexpression of CRR1 increased plant resistance to V. dahliae, the fungus Botrytis cinerea, and the oomycete Phytophthora parasitica var nicotianae. By contrast, knockout of VdSSEP1 in V. dahliae destroyed the pathogenicity of this fungus. Together, our results provide compelling evidence for a multilayered interplay of factors in cotton apoplastic immunity.
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Osa‐miR398b boosts H2O2 production and rice blast disease‐resistance via multiple superoxide dismutases - Li - 2019 - New Phytologist -

Osa‐miR398b boosts H2O2 production and rice blast disease‐resistance via multiple superoxide dismutases - Li - 2019 - New Phytologist - | Plant immunity and legume symbiosis | Scoop.it
miRNAs contribute to plant resistance against pathogens. Previously, we found that the function of miR398b in immunity in rice differs from that in Arabidopsis. However, the underlying mechanisms are unclear.
In this study, we characterized the mutants of miR398b target genes and demonstrated that multiple superoxide dismutase genes contribute to miR398b‐regulated rice immunity against the blast fungus Magnaporthe oryzae.
Out of the four target genes of miR398b, mutations in Cu/Zn‐Superoxidase Dismutase1 (CSD1), CSD2 and Os11g09780 (Superoxide DismutaseX, SODX) led to enhanced resistance to M. oryzae and increased hydrogen peroxide (H2O2) accumulation. By contrast, mutations in Copper Chaperone for Superoxide Dismutase (CCSD) resulted in enhanced susceptibility. Biochemical studies revealed that csd1, csd2 and sodx displayed altered expression of CSDs and other superoxide dismutase (SOD) family members, leading to increased total SOD enzyme activity that positively contributed to higher H2O2 production. By contrast, the ccsd mutant showed CSD protein deletion, resulting in decreased CSD and total SOD enzyme activity.
Our results demonstrate the roles of different SODs in miR398b‐regulated resistance to rice blast disease, and uncover an integrative regulatory network in which miR398b boosts total SOD activity to upregulate H2O2 concentration and thereby improve disease resistance.
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Inducible overexpression of Ideal Plant Architecture1 improves both yield and disease resistance in rice

Inducible overexpression of Ideal Plant Architecture1 improves both yield and disease resistance in rice | Plant immunity and legume symbiosis | Scoop.it
Breeding crops with resistance is an efficient way to control diseases. However, increased resistance often has a fitness penalty. Thus, simultaneously increasing disease resistance and yield potential is a challenge in crop breeding. In this study, we found that downregulation of microRNA-156 (miR-156) and overexpression of Ideal Plant Architecture1 (IPA1) and OsSPL7, two target genes of miR-156, enhanced disease resistance against bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo), but reduced rice yield. We discovered that gibberellin signalling might be partially responsible for the disease resistance and developmental defects in IPA1 overexpressors. We then generated transgenic rice plants expressing IPA1 with the pathogen-inducible promoter of OsHEN1; these plants had both enhanced disease resistance and enhanced yield-related traits. Thus, we have identified miR-156–IPA1 as a novel regulator of the crosstalk between growth and defence, and we have established a new strategy for obtaining both high disease resistance and high yield.
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Showcasing the application of synchrotron‐based X‐ray computed tomography in host–pathogen interactions: The role of wheat rachilla and rachis nodes in Type‐II resistance to Fusarium graminearum - ...

Showcasing the application of synchrotron‐based X‐ray computed tomography in host–pathogen interactions: The role of wheat rachilla and rachis nodes in Type‐II resistance to Fusarium graminearum - ... | Plant immunity and legume symbiosis | Scoop.it
Fusarium head blight, caused primarily by Fusarium graminearum (Fg), is one of the most devastating diseases of wheat. Host resistance in wheat is classified into five types (Type‐I to Type‐V), and a majority of moderately resistant genotypes carry Type‐II resistance (resistance to pathogen spread in the rachis) alleles, mainly from the Chinese cultivar Sumai 3. Histopathological studies in the past failed to identify the key tissue in the spike conferring resistance to pathogen spread, and most of the studies used destructive techniques, potentially damaging the tissue(s) under study. In the present study, nondestructive synchrotron‐based phase contrast X‐ray imaging and computed tomography techniques were used to confirm the part of the wheat spike conferring Type‐II resistance to Fg spread, thus showcasing the application of synchrotron‐based techniques to image host–pathogen interactions. Seven wheat genotypes of moderate resistance to Fusarium head blight were studied for changes in the void space volume fraction and grayscale/voxel intensity following Fg inoculation. Cell‐wall biopolymeric compounds were quantified using Fourier‐transform midinfrared spectroscopy for all genotype‐treatment combinations. The study revealed that the rachilla and rachis nodes together are structurally important in conferring Type‐II resistance. The structural reinforcement was not necessarily observed from lignin deposition but rather from an unknown mechanism.
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The cotton laccase gene GhLAC15 enhances Verticillium wilt resistance via an increase in defence‐induced lignification and lignin components in the cell walls of plants - Zhang - 2019 - Molecular P...

The cotton laccase gene GhLAC15 enhances Verticillium wilt resistance via an increase in defence‐induced lignification and lignin components in the cell walls of plants - Zhang - 2019 - Molecular P... | Plant immunity and legume symbiosis | Scoop.it
Verticillium dahliae is a phytopathogenic fungal pathogen that causes vascular wilt diseases responsible for considerable decreases in cotton yields. The lignification of cell wall appositions is a conserved basal defence mechanism in the plant innate immune response. However, the function of laccase in defence‐induced lignification has not been described. Screening of an SSH library of a resistant cotton cultivar, Jimian20, inoculated with V. dahliae revealed a laccase gene that was strongly induced by the pathogen. This gene was phylogenetically related to AtLAC15 and contained domains conserved by laccases; therefore, we named it GhLAC15. Quantitative reverse transcription‐polymerase chain reaction indicated that GhLAC15 maintained higher expression levels in tolerant than in susceptible cultivars. Overexpression of GhLAC15 enhanced cell wall lignification, resulting in increased total lignin, G monolignol and G/S ratio, which significantly improved the Verticillium wilt resistance of transgenic Arabidopsis. In addition, the levels of arabinose and xylose were higher in transgenic plants than in wild‐type plants, which resulted in transgenic Arabidopsis plants being less easily hydrolysed. Furthermore, suppression of the transcriptional level of GhLAC15 resulted in an increase in susceptibility in cotton. The content of monolignol and the G/S ratio were lower in silenced cotton plants, which led to resistant cotton cv. Jimian20 becoming susceptible. These results demonstrate that GhLAC15 enhances Verticillium wilt resistance via an increase in defence‐induced lignification and arabinose and xylose accumulation in the cell wall of Gossypium hirsutum. This study broadens our knowledge of defence‐induced lignification and cell wall modifications as defence mechanisms against V. dahliae.
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Rpp1 Encodes a ULP1-NBS-LRR Protein That Controls Immunity to Phakopsora pachyrhizi in Soybean | Molecular Plant-Microbe Interactions

Rpp1 Encodes a ULP1-NBS-LRR Protein That Controls Immunity to Phakopsora pachyrhizi in Soybean | Molecular Plant-Microbe Interactions | Plant immunity and legume symbiosis | Scoop.it
Phakopsora pachyrhizi is the causal agent of Asian soybean rust. Susceptible soybean plants infected by virulent isolates of P. pachyrhizi are characterized by tan-colored lesions and erumpent uredinia on the leaf surface. Germplasm screening and genetic analyses have led to the identification of seven loci, Rpp1 to Rpp7, that provide varying degrees of resistance to P. pachyrhizi (Rpp). Two genes, Rpp1 and Rpp1b, map to the same region on soybean chromosome 18. Rpp1 is unique among the Rpp genes in that it confers an immune response (IR) to avirulent P. pachyrhizi isolates. The IR is characterized by a lack of visible symptoms, whereas resistance provided by Rpp1b to Rpp7 results in red-brown foliar lesions. Rpp1 maps to a region spanning approximately 150 kb on chromosome 18 between markers Sct_187 and Sat_064 in L85-2378 (Rpp1), an isoline developed from Williams 82 and PI 200492 (Rpp1). To identify Rpp1, we constructed a bacterial artificial chromosome library from soybean accession PI 200492. Sequencing of the Rpp1 locus identified three homologous nucleotide binding site-leucine rich repeat (NBS-LRR) candidate resistance genes between Sct_187 and Sat_064. Each candidate gene is also predicted to encode an N-terminal ubiquitin-like protease 1 (ULP1) domain. Cosilencing of the Rpp1 candidates abrogated the immune response in the Rpp1 resistant soybean accession PI 200492, indicating that Rpp1 is a ULP1-NBS-LRR protein and plays a key role in the IR.
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Mimicking the Host Regulation of Salicylic Acid: A Virulence Strategy by the Clubroot Pathogen Plasmodiophora brassicae | Molecular Plant-Microbe Interactions

Mimicking the Host Regulation of Salicylic Acid: A Virulence Strategy by the Clubroot Pathogen Plasmodiophora brassicae | Molecular Plant-Microbe Interactions | Plant immunity and legume symbiosis | Scoop.it
The plant hormone salicylic acid (SA) plays a critical role in defense against biotrophic pathogens such as Plasmodiophora brassicae, which is an obligate pathogen of crucifer species and the causal agent of clubroot disease of canola (Brassica napus). P. brassicae encodes a protein, predicted to be secreted, with very limited homology to benzoic acid (BA)/SA–methyltransferase, designated PbBSMT. PbBSMT has a SA- and an indole-3-acetic acid–binding domain, which are also present in Arabidopsis thaliana BSMT1 (AtBSMT1) and, like AtBSMT1, has been shown to methylate BA and SA. In support of the hypothesis that P. brassicae uses PbBSMT to overcome SA-mediated defenses by converting SA into inactive methyl salicylate (MeSA), here, we show that PbBSMT suppresses local defense and provide evidence that PbBSMT is much more effective than AtBSMT1 at suppressing the levels of SA and its associated effects. Basal SA levels in Arabidopsis plants that constitutively overexpress PbBSMT compared with those in Arabidopsis wild-type Col-0 (WT) were reduced approximately 80% versus only a 50% reduction in plants overexpressing AtBSMT1. PbBSMT-overexpressing plants were more susceptible to P. brassicae than WT plants; they also were partially compromised in nonhost resistance to Albugo candida. In contrast, AtBSMT1-overexpressing plants were not more susceptible than WT to either P. brassicae or A. candida. Furthermore, transgenic Arabidopsis and tobacco plants overexpressing PbBSMT exhibited increased susceptibility to virulent Pseudomonas syringae pv. tomato DC3000 (DC3000) and virulent Pseudomonas syringae pv. tabaci, respectively. Gene-mediated resistance to DC3000/AvrRpt2 and tobacco mosaic virus (TMV) was also compromised in Arabidopsis and Nicotiana tabacum ‘Xanthi-nc’ plants overexpressing PbBSMT, respectively. Transient expression of PbBSMT or AtBSMT1 in lower leaves of N. tabacum Xanthi-nc resulted in systemic acquired resistance (SAR)-like enhanced resistance to TMV in the distal systemic leaves. Chimeric grafting experiments revealed that, similar to SAR, the development of a PbBSMT-mediated SAR-like phenotype was also dependent on the MeSA esterase activity of NtSABP2 in the systemic leaves. Collectively, these results strongly suggest that PbBSMT is a novel effector, which is secreted by P. brassicae into its host plant to deplete pathogen-induced SA accumulation.
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Expression polymorphism at the ARPC4 locus links the actin cytoskeleton with quantitative disease resistance to Sclerotinia sclerotiorum in Arabidopsis thaliana - Badet - 2019 - New Phytologist -

Expression polymorphism at the ARPC4 locus links the actin cytoskeleton with quantitative disease resistance to Sclerotinia sclerotiorum in Arabidopsis thaliana - Badet - 2019 - New Phytologist - | Plant immunity and legume symbiosis | Scoop.it
Quantitative disease resistance (QDR) is a form of plant immunity widespread in nature, and the only one active against broad host range fungal pathogens. The genetic determinants of QDR are complex and largely unknown, and are thought to rely partly on genes controlling plant morphology and development.
We used genome‐wide association mapping in Arabidopsis thaliana to identify ARPC4 as associated with QDR against the necrotrophic fungal pathogen Sclerotinia sclerotiorum. Mutants impaired in ARPC4 showed enhanced susceptibility to S. sclerotiorum, defects in the structure of the actin filaments and in their responsiveness to S. sclerotiorum. Disruption of ARPC4 also alters callose deposition and the expression of defense‐related genes upon S. sclerotiorum infection.
Analysis of ARPC4 diversity in A. thaliana identified one haplotype (ARPC4R) showing a c. 1 kbp insertion in ARPC4 regulatory region and associated with higher level of QDR. Accessions from the ARPC4R haplotype showed enhanced ARPC4 expression upon S. sclerotiorum challenge, indicating that polymorphisms in ARPC4 regulatory region are associated with enhanced QDR.
This work identifies a novel actor of plant QDR against a fungal pathogen and provides a prime example of genetic mechanisms leading to the recruitment of cell morphology processes in plant immunity.
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Origin and evolution of the plant immune system - Han - 2019 - New Phytologist -

Origin and evolution of the plant immune system - Han - 2019 - New Phytologist - | Plant immunity and legume symbiosis | Scoop.it
Microbes have engaged in antagonistic associations with plants for hundreds of millions of years. Plants, in turn, have evolved diverse immune strategies to combat microbial pathogens. The conflicts between plants and pathogens result in everchanging coevolutionary cycles known as ‘Red Queen’ dynamics. These ancient and ongoing plant–pathogen interactions have shaped the evolution of both plant and pathogen genomes. With the recent explosion of plant genome‐scale data, comparative analyses provide novel insights into the coevolutionary dynamics of plants and pathogens. Here, we discuss the ancient associations between plants and microbes as well as the evolutionary principles underlying plant–pathogen interactions. We synthesize and review the current knowledge on the origin and evolution of key components of the plant immune system. We also highlight the importance of studying algae and nonflowering land plants in understanding the evolution of the plant immune system.
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The Arabidopsis RRM domain protein EDM3 mediates race‐specific disease resistance by controlling H3K9me2‐dependent alternative polyadenylation of RPP7 immune receptor transcripts - Lai - 2019 -

The Arabidopsis RRM domain protein EDM3 mediates race‐specific disease resistance by controlling H3K9me2‐dependent alternative polyadenylation of RPP7 immune receptor transcripts - Lai - 2019 - | Plant immunity and legume symbiosis | Scoop.it
The NLR‐receptor RPP7 mediates race‐specific immunity in Arabidopsis. Previous screens for enhanced downy mildew (edm) mutants identified the co‐chaperone SGT1b (EDM1) and the PHD‐finger protein EDM2 as critical regulators of RPP7. Here, we describe a third edm mutant compromised in RPP7 immunity, edm3. EDM3 encodes a nuclear‐localized protein featuring an RNA‐recognition motif. Like EDM2, EDM3 promotes histone H3 lysine 9 dimethylation (H3K9me2) at RPP7. Global profiling of H3K9me2 showed EDM3 to affect this silencing mark at a large set of loci. Importantly, both EDM3 and EDM2 co‐associate in vivo with H3K9me2‐marked chromatin and transcripts at a critical proximal polyadenylation site of RPP7, where they suppress proximal transcript polyadeylation/termination. Our results highlight the complexity of plant NLR gene regulation, and establish a functional and physical link between a histone mark and NLR‐transcript processing.
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Frontiers | Advanced Imaging for Quantitative Evaluation of Aphanomyces Root Rot Resistance in Lentil | Plant Science

Frontiers | Advanced Imaging for Quantitative Evaluation of Aphanomyces Root Rot Resistance in Lentil | Plant Science | Plant immunity and legume symbiosis | Scoop.it
Aphanomyces root rot (ARR) is a soil-borne disease that results in severe yield losses in lentil. The development of resistant cultivars is one of the key strategies to control this pathogen. However, the evaluation of disease severity is limited to visual scores that can be subjective. This study utilized image-based phenotyping approaches to evaluate Aphanomyces euteiches resistance in lentil genotypes in greenhouse (351 genotypes from lentil single plant/LSP derived collection and 191 genotypes from recombinant inbred lines/RIL using digital Red-Green-Blue/RGB and hyperspectral imaging) and field (173 RIL genotypes using unmanned aerial system-based multispectral imaging) conditions. Moderate to strong correlations were observed between RGB, multispectral, and hyperspectral derived features extracted from lentil shoots/roots and visual scores. In general, root features extracted from RGB imaging were found to be strongly associated with disease severity. With only three root traits, elastic net regression model was able to predict disease severity across and within multiple datasets (R2 = 0.45–0.73 and RMSE = 0.66–1.00). The selected features could represent visual disease scores. Moreover, we developed twelve normalized difference spectral indices (NDSIs) that were significantly correlated with disease scores: two NDSIs for lentil shoot section – computed from wavelengths of 1170, 1160, 1270, and 1280 nm (0.12 ≤ |r| ≤ 0.24, P < 0.05) and ten NDSIs for lentil root sections – computed from wavelengths in the range of 630–670, 700–840, and 1320–1530 nm (0.10 ≤ |r| ≤ 0.50, P < 0.05). Root-derived NDSIs were more accurate in predicting disease scores with an R2 of 0.54 (RMSE = 0.86), especially when the model was trained and tested on LSP accessions, compared to R2 of 0.25 (RMSE = 1.64) when LSP and RIL genotypes were used as train and test datasets, respectively. Importantly, NDSIs – computed from wavelengths of 700, 710, 730, and 790 nm – had strong positive correlations with disease scores (0.35 ≤r ≤ 0.50, P < 0.0001), which was confirmed in field phenotyping with similar correlations using vegetation index with red edge wavelength (normalized difference red edge, 0.36 ≤ |r| ≤ 0.57, P < 0.0001). The adopted image-based phenotyping approaches can help plant breeders to objectively quantify ARR resistance and reduce the subjectivity in selecting potential genotypes.
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Receptor-Like Cytoplasmic Kinases: Central Players in Plant Receptor Kinase–Mediated Signaling | Annual Review of Plant Biology

Receptor-Like Cytoplasmic Kinases: Central Players in Plant Receptor Kinase–Mediated Signaling | Annual Review of Plant Biology | Plant immunity and legume symbiosis | Scoop.it
Receptor kinases (RKs) are of paramount importance in transmembrane signaling that governs plant reproduction, growth, development, and adaptation to diverse environmental conditions. Receptor-like cytoplasmic kinases (RLCKs), which lack extracellular ligand-binding domains, have emerged as a major class of signaling proteins that regulate plant cellular activities in response to biotic/abiotic stresses and endogenous extracellular signaling molecules. By associating with immune RKs, RLCKs regulate multiple downstream signaling nodes to orchestrate a complex array of defense responses against microbial pathogens. RLCKs also associate with RKs that perceive brassinosteroids and signaling peptides to coordinate growth, pollen tube guidance, embryonic and stomatal patterning, floral organ abscission, and abiotic stress responses. The activity and stability of RLCKs are dynamically regulated not only by RKs but also by other RLCK-associated proteins. Analyses of RLCK-associated components and substrates have suggested phosphorylation relays as a major mechanism underlying RK-mediated signaling.
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A Remote cis-Regulatory Region Is Required for NIN Expression in the Pericycle to Initiate Nodule Primordium Formation in Medicago truncatula

A Remote cis-Regulatory Region Is Required for NIN Expression in the Pericycle to Initiate Nodule Primordium Formation in Medicago truncatula | Plant immunity and legume symbiosis | Scoop.it
The legume-rhizobium symbiosis results in nitrogen-fixing root nodules, and their formation involves both intracellular infection initiated in the epidermis and nodule organogenesis initiated in inner root cell layers. NODULE INCEPTION (NIN) is a nodule-specific transcription factor essential for both processes. These NIN-regulated processes occur at different times and locations in the root, demonstrating a complex pattern of spatiotemporal regulation. We show that regulatory sequences sufficient for the epidermal infection process are located within a 5 kb region directly upstream of the NIN start codon in Medicago truncatula. Furthermore, we identify a remote upstream cis-regulatory region required for the expression of NIN in the pericycle, and we show that this region is essential for nodule organogenesis. This region contains putative cytokinin response elements and is conserved in eight more legume species. Both the cytokinin receptor 1, which is essential for nodule primordium formation, and the B-type response regulator RR1 are expressed in the pericycle in the susceptible zone of the uninoculated root. This, together with the identification of the cytokinin-responsive elements in the NIN promoter, strongly suggests that NIN expression is initially triggered by cytokinin signaling in the pericycle to initiate nodule primordium formation.
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Molecular Dissection of Early Defense Signaling Underlying Volatile-Mediated Defense Regulation and Herbivore Resistance in Rice

Molecular Dissection of Early Defense Signaling Underlying Volatile-Mediated Defense Regulation and Herbivore Resistance in Rice | Plant immunity and legume symbiosis | Scoop.it
Herbivore-induced plant volatiles prime plant defenses and resistance, but how they are integrated into early defense signaling and whether a causal relationship exists between volatile defense priming and herbivore resistance is unclear. Here, we investigated the impact of indole, a common herbivore-induced plant volatile and modulator of many physiological processes in plants, bacteria, and animals, on early defense signaling and herbivore resistance in rice (Oryza sativa). Rice plants infested by fall armyworm (Spodoptera frugiperda) caterpillars release indole at a rate of up to 25 ng*h−1. Exposure to equal doses of exogenous indole enhances rice resistance to S. frugiperda. Screening of early signaling components revealed that indole pre-exposure directly enhances the expression of the leucine-rich repeat-receptor-like kinase OsLRR-RLK1. Pre-exposure to indole followed by simulated herbivory increases (i.e. primes) the transcription, accumulation, and activation of the mitogen-activated protein kinase OsMPK3 and the expression of the downstream WRKY transcription factor gene OsWRKY70 as well as several jasmonate biosynthesis genes, resulting in higher jasmonic acid (JA) accumulation. Analysis of transgenic plants defective in early signaling showed that OsMPK3 is required and that OsMPK6 and OsWRKY70 contribute to indole-mediated defense priming of JA-dependent herbivore resistance. Therefore, herbivore-induced plant volatiles increase plant resistance to herbivores by positively regulating early defense signaling components.
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Nodule‐specific PLAT domain proteins are expanded in the Medicago lineage and required for nodulation - Trujillo - 2019 - New Phytologist -

Nodule‐specific PLAT domain proteins are expanded in the Medicago lineage and required for nodulation - Trujillo - 2019 - New Phytologist - | Plant immunity and legume symbiosis | Scoop.it
Symbiotic nitrogen fixation in legumes is mediated by an interplay of signaling processes between plant hosts and rhizobial symbionts. In legumes, several secreted protein families have undergone expansions and play key roles in nodulation. Thus, identifying lineage‐specific expansions (LSEs) of nodulation‐associated genes can be a strategy to discover candidate gene families.
Using bioinformatic tools, we identified 13 LSEs of nodulation‐related secreted protein families, each unique to either Glycine, Arachis or Medicago lineages. In the Medicago lineage, nodule‐specific Polycystin‐1, Lipoxygenase, Alpha Toxin (PLAT) domain proteins (NPDs) expanded to five members. We examined NPD function using CRISPR/Cas9 multiplex genome editing to create Medicago truncatula NPD knockout lines, targeting one to five NPD genes.
Mutant lines with differing combinations of NPD gene inactivations had progressively smaller nodules, earlier onset of nodule senescence, or ineffective nodules compared to the wild‐type control. Double‐ and triple‐knockout lines showed dissimilar nodulation phenotypes but coincided in upregulation of a DHHC‐type zinc finger and an aspartyl protease gene, possible candidates for the observed disturbance of proper nodule function.
By postulating that gene family expansions can be used to detect candidate genes, we identified a family of nodule‐specific PLAT domain proteins and confirmed that they play a role in successful nodule formation.
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Exploring the protein–protein interaction landscape in plants - Struk - 2019 - Plant, Cell & Environment -

Exploring the protein–protein interaction landscape in plants - Struk - 2019 - Plant, Cell & Environment - | Plant immunity and legume symbiosis | Scoop.it
Protein–protein interactions (PPIs) represent an essential aspect of plant systems biology. Identification of key protein players and their interaction networks provide crucial insights into the regulation of plant developmental processes and into interactions of plants with their environment. Despite the great advance in the methods for the discovery and validation of PPIs, still several challenges remain. First, the PPI networks are usually highly dynamic, and the in vivo interactions are often transient and difficult to detect. Therefore, the properties of the PPIs under study need to be considered to select the most suitable technique, because each has its own advantages and limitations. Second, besides knowledge on the interacting partners of a protein of interest, characteristics of the interaction, such as the spatial or temporal dynamics, are highly important. Hence, multiple approaches have to be combined to obtain a comprehensive view on the PPI network present in a cell. Here, we present the progress in commonly used methods to detect and validate PPIs in plants with a special emphasis on the PPI features assessed in each approach and how they were or can be used for the study of plant interactions with their environment.
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Hydrogen peroxide metabolism and functions in plants - Smirnoff - 2019 - New Phytologist -

Hydrogen peroxide metabolism and functions in plants - Smirnoff - 2019 - New Phytologist - | Plant immunity and legume symbiosis | Scoop.it
Hydrogen peroxide (H2O2) is produced, via superoxide and superoxide dismutase, by electron transport in chloroplasts and mitochondria, plasma membrane NADPH oxidases, peroxisomal oxidases, type III peroxidases and other apoplastic oxidases. Intracellular transport is facilitated by aquaporins and H2O2 is removed by catalase, peroxiredoxin, glutathione peroxidase‐like enzymes and ascorbate peroxidase, all of which have cell compartment‐specific isoforms. Apoplastic H2O2 influences cell expansion, development and defence by its involvement in type III peroxidase‐mediated polymer cross‐linking, lignification and, possibly, cell expansion via H2O2‐derived hydroxyl radicals. Excess H2O2 triggers chloroplast and peroxisome autophagy and programmed cell death. The role of H2O2 in signalling, for example during acclimation to stress and pathogen defence, has received much attention, but the signal transduction mechanisms are poorly defined. H2O2 oxidizes specific cysteine residues of target proteins to the sulfenic acid form and, similar to other organisms, this modification could initiate thiol‐based redox relays and modify target enzymes, receptor kinases and transcription factors. Quantification of the sources and sinks of H2O2 is being improved by the spatial and temporal resolution of genetically encoded H2O2 sensors, such as HyPer and roGFP2‐Orp1. These H2O2 sensors, combined with the detection of specific proteins modified by H2O2, will allow a deeper understanding of its signalling roles.
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Underground Azelaic Acid–Conferred Resistance to Pseudomonas syringae in Arabidopsis | Molecular Plant-Microbe Interactions

Underground Azelaic Acid–Conferred Resistance to Pseudomonas syringae in Arabidopsis | Molecular Plant-Microbe Interactions | Plant immunity and legume symbiosis | Scoop.it
Local interactions between individual plant organs and diverse microorganisms can lead to whole plant immunity via the mobilization of defense signals. One such signal is the plastid lipid-derived oxylipin azelaic acid (AZA). Arabidopsis lacking AZI1 or EARLI1, related lipid transfer family proteins, exhibit reduced AZA transport among leaves and cannot mount systemic immunity. AZA has been detected in roots as well as leaves. Therefore, the present study addresses the effects on plants of AZA application to roots. AZA but not the structurally related suberic acid inhibits root growth when directly in contact with roots. Treatment of roots with AZA also induces resistance to Pseudomonas syringae in aerial tissues. These effects of AZA on root growth and disease resistance depend, at least partially, on AZI1 and EARLI1. AZI1 in roots localizes to plastids, similar to its known location in leaves. Interestingly, kinases previously shown to modify AZI1 in vitro, MPK3 and MPK6, are also needed for AZA-induced root-growth inhibition and aboveground immunity. Finally, deuterium-labeled AZA applied to the roots does not move to aerial tissues. Thus, AZA application to roots triggers systemic immunity through an AZI1/EARLI1/MPK3/MPK6-dependent pathway and AZA effects may involve one or more additional mobile signals.
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Battlefield Cytoskeleton: Turning the Tide on Plant Immunity | Molecular Plant-Microbe Interactions

Battlefield Cytoskeleton: Turning the Tide on Plant Immunity | Molecular Plant-Microbe Interactions | Plant immunity and legume symbiosis | Scoop.it
The plant immune system comprises a complex network of signaling processes, regulated not only by classically defined immune components (e.g., resistance genes) but also by a suite of developmental, environmental, abiotic, and biotic-associated factors. In total, it is the sum of these interactions—the connectivity to a seemingly endless array of environments—that ensures proper activation, and control, of a system that is responsible for cell surveillance and response to threats presented by invading pests and pathogens. Over the past decade, the field of plant pathology has witnessed the discovery of numerous points of convergence between immunity, growth, and development, as well as overlap with seemingly disparate processes such as those that underpin plant response to changes in the environment. Toward defining how immune signaling is regulated, recent studies have focused on dissecting the mechanisms that underpin receptor-ligand interactions, phospho-regulation of signaling cascades, and the modulation of host gene expression during infection. As one of the major regulators of these immune signaling cascades, the plant cytoskeleton is the stage from which immune-associated processes are mobilized and oriented and, in this role, it controls the movement of the organelles, proteins, and chemical signals that support plant defense signaling. In short, the cytoskeleton is the battlefield from which pathogens and plants volley virulence and resistance, transforming resistance to susceptibility. Herein, we discuss the role of the eukaryotic cytoskeleton as a platform for the function of the plant immune system.
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LncRNA33732‐respiratory burst oxidase module associated with WRKY1 in tomato‐ Phytophthora infestans interactions - Cui - 2019 - The Plant Journal - W

LncRNA33732‐respiratory burst oxidase module associated with WRKY1 in tomato‐ Phytophthora infestans interactions - Cui - 2019 - The Plant Journal - W | Plant immunity and legume symbiosis | Scoop.it
Our previous studies indicated that tomato WRKY1 transcription factor acts as a positive regulator during tomato resistance to Phytophthora infestans. However, the molecular mechanism of WRKY1‐mediated resistance regulation remains unclear. Here, we used a comparative transcriptome analysis between wild‐type and WRKY1‐overexpressing tomato plants to identify differentially expressed genes (DEGs) and long non‐coding RNAs (DELs), and we examined long non‐coding RNA (lncRNA)‐gene networks. The promoter sequences of the upregulated DEGs and DELs were analyzed. Among 1073 DEGs and 199 DELs, 1 kb 5′‐upstream regions of 59 DEGs and 22 DELs contain the W‐box, the target sequence of the WRKY1. The results of promoter−β‐glucuronidase (GUS) fusion and yeast one‐hybrid assay showed that lncRNA33732 was activated by WRKY1 through sequence‐specific interactions with the W‐box element in its promoter. The overexpression and silencing analysis of lncRNA33732 in tomato showed that lncRNA33732 acts as a positive regulator and enhanced tomato resistance to P. infestans by induction of the expression of respiratory burst oxidase (RBOH) and increase in the accumulation of H2O2. When the expression of RBOH gene was inhibited in tomato plants, H2O2 accumulation decreased and resistance were impaired. These findings suggest that lncRNA33732 activated by WRKY1 induces RBOH expression to increase H2O2 accumulation in early defense reaction of tomato to P. infestans attack. Our results provide insights into the WRKY1−lncRNA33732−RBOH module involved in the regulation of H2O2 accumulation and resistance to P. infestans, as well as provide candidates to enhance broad‐spectrum resistance to pathogens in tomato.
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BIG regulates stomatal immunity and jasmonate production in Arabidopsis - Zhang - 2019 - New Phytologist

BIG regulates stomatal immunity and jasmonate production in Arabidopsis - Zhang - 2019 - New Phytologist | Plant immunity and legume symbiosis | Scoop.it
Plants have evolved an array of responses that provide them with protection from attack by microorganisms and other predators. Many of these mechanisms depend upon interactions between the plant hormones jasmonate (JA) and ethylene (ET). However, the molecular basis of these interactions is insufficiently understood.
Gene expression and physiological assays with mutants were performed to investigate the role of Arabidopsis BIG gene in stress responses.
BIG transcription is downregulated by methyl JA (MeJA), necrotrophic infection or mechanical injury. BIG deficiency promotes JA‐dependent gene induction, increases JA production but restricts the accumulation of both ET and salicylic acid. JA‐induced anthocyanin accumulation and chlorophyll degradation are enhanced and stomatal immunity is impaired by BIG disruption. Bacteria‐ and lipopolysaccaride (LPS)‐induced stomatal closure is reduced in BIG gene mutants, which are hyper‐susceptible to microbial pathogens with different lifestyles, but these mutants are less attractive to phytophagous insects.
Our results indicate that BIG negatively and positively regulate the MYC2 and ERF1 arms of the JA signalling pathway. BIG warrants recognition as a new and distinct regulator that regulates JA responses, the synergistic interactions of JA and ET, and other hormonal interactions that reconcile the growth and defense dilemma in Arabidopsis.
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Quantitative resistance to clubroot infection mediated by transgenerational epigenetic variation in Arabidopsis - Liégard - 2019 - New Phytologist -

Quantitative resistance to clubroot infection mediated by transgenerational epigenetic variation in Arabidopsis - Liégard - 2019 - New Phytologist - | Plant immunity and legume symbiosis | Scoop.it
Quantitative disease resistance, often influenced by environmental factors, is thought to be the result of DNA sequence variants segregating at multiple loci. However, heritable differences in DNA methylation, so‐called transgenerational epigenetic variants, also could contribute to quantitative traits. Here, we tested this possibility using the well‐characterized quantitative resistance of Arabidopsis to clubroot, a Brassica major disease caused by Plasmodiophora brassicae.
For that, we used the epigenetic recombinant inbred lines (epiRIL) derived from the cross ddm1‐2 × Col‐0, which show extensive epigenetic variation but limited DNA sequence variation. Quantitative loci under epigenetic control (QTLepi) mapping was carried out on 123 epiRIL infected with P. brassicae and using various disease‐related traits.
EpiRIL displayed a wide range of continuous phenotypic responses. Twenty QTLepi were detected across the five chromosomes, with a bona fide epigenetic origin for 16 of them. The effect of five QTLepi was dependent on temperature conditions. Six QTLepi co‐localized with previously identified clubroot resistance genes and QTL in Arabidopsis.
Co‐localization of clubroot resistance QTLepi with previously detected DNA‐based QTL reveals a complex model in which a combination of allelic and epiallelic variations interacts with the environment to lead to variation in clubroot quantitative resistance.
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