Plant pathology
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Why species delimitation matters for fungal ecology: Colletotrichum diversity on wild and cultivated cashew in Brazil

Why species delimitation matters for fungal ecology: Colletotrichum diversity on wild and cultivated cashew in Brazil | Plant pathology | Scoop.it
Highlights

Several Colletotrichum species are associated with cashew anthracnose in Brazil

Interpretation of Colletotrichum community diversity depends on how species are delimited

C. gloeosporioides was rare, while C. siamense was the dominant species

The cultivated cashew and leaves were the most diverse host-associated strata

The Atlantic Forest and Pernambuco were the most diverse geographical strata

Via Serenella A Sukno
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Nat Plants: Crosstalk between PTGS and TGS pathways in natural antiviral immunity and disease recovery

Nat Plants: Crosstalk between PTGS and TGS pathways in natural antiviral immunity and disease recovery | Plant pathology | Scoop.it

ABSTRACT: Virus-induced diseases cause severe damage to cultivated plants, resulting in crop losses. Certain plant–virus interactions allow disease recovery at later stages of infection and have the potential to reveal important molecular targets for achieving disease control. Although recovery is known to involve antiviral RNA silencing, the specific components of the many plant RNA silencing pathways required for recovery are not known. We found that Arabidopsis thaliana plants infected with oilseed rape mosaic virus (ORMV) undergo symptom recovery. The recovered leaves contain infectious, replicating virus, but exhibit a loss of viral suppressor of RNA silencing (VSR) protein activity. We demonstrate that recovery depends on the 21–22 nt siRNA-mediated post-transcriptional gene silencing (PTGS) pathway and on components of a transcriptional gene silencing (TGS) pathway that is known to facilitate non-cell-autonomous silencing signalling. Collectively, our observations indicate that recovery reflects the establishment of a tolerant state in infected tissues and occurs following robust delivery of antiviral secondary siRNAs from source to sink tissues, and establishment of a dosage able to block the VSR activity involved in the formation of disease symptoms.

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Nat Plants: The systemin receptor SYR1 enhances resistance of tomato against herbivorous insects

Nat Plants: The systemin receptor SYR1 enhances resistance of tomato against herbivorous insects | Plant pathology | Scoop.it
ABSTRACT: The discovery in tomato of systemin, the first plant peptide hormone, was a fundamental change for the concept of plant hormones. Numerous other peptides have since been shown to play regulatory roles in many aspects of the plant life, including growth, development, fertilization and interactions with symbiotic organisms. Systemin, an 18 amino acid peptide derived from a larger precursor protein, was proposed to act as the spreading signal that triggers systemic defence responses observed in plants after wounding or attack by herbivores. Further work culminated in the identification of a leucine-rich repeat receptor kinase (LRR-RK) as the systemin receptor 160 (SR160). SR160 is a tomato homologue of Brassinosteroid Insensitive 1 (BRI1), which mediates the regulation of growth and development in response to the steroid hormone brassinolide. However, a role of SR160/BRI1 as systemin receptor could not be corroborated by others. Here, we demonstrate that perception of systemin depends on a pair of distinct LRR-RKs termed SYR1 and SYR2. SYR1 acts as a genuine systemin receptor that binds systemin with high affinity and specificity. Further, we show that presence of SYR1, although not decisive for local and systemic wound responses, is important for defence against insect herbivory.


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Nat Plants: One effector at a time

Nat Plants: One effector at a time | Plant pathology | Scoop.it
Bacterial pathogens have a multitude of effectors that target plant host cells and promote disease. A case is made for a new suspect, phytate, as a target of a novel phytase activity for a type III effector of Xanthomonas.


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Chemical signaling involved in plant–microbe interactions

Chemical signaling involved in plant–microbe interactions | Plant pathology | Scoop.it
Microorganisms are found everywhere, and they are closely associated with plants. Because the establishment of any plant–microbe association involves chemical communication, understanding crosstalk processes is fundamental to defining the type of relationship. Although several metabolites from plants and microbes have been fully characterized, their roles in the chemical interplay between these partners are not well understood in most cases, and they require further investigation. In this review, we describe different plant–microbe associations from colonization to microbial establishment processes in plants along with future prospects, including agricultural benefits.


Via Jean-Michel Ané
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Nature: An extracellular network of Arabidopsis leucine-rich repeat receptor kinases

Nature: An extracellular network of Arabidopsis leucine-rich repeat receptor             kinases | Plant pathology | Scoop.it

ABSTRACT: The cells of multicellular organisms receive extracellular signals using surface receptors. The extracellular domains (ECDs) of cell surface receptors function as interaction platforms, and as regulatory modules of receptor activation1,2. Understanding how interactions between ECDs produce signal-competent receptor complexes is challenging because of their low biochemical tractability3,4. In plants, the discovery of ECD interactions is complicated by the massive expansion of receptor families, which creates tremendous potential for changeover in receptor interactions5. The largest of these families in Arabidopsis thaliana consists of 225 evolutionarily related leucine-rich repeat receptor kinases (LRR-RKs)5, which function in the sensing of microorganisms, cell expansion, stomata development and stem-cell maintenance6,7,8,9. Although the principles that govern LRR-RK signalling activation are emerging1,10, the systems-level organization of this family of proteins is unknown. Here, to address this, we investigated 40,000 potential ECD interactions using a sensitized high-throughput interaction assay3, and produced an LRR-based cell surface interaction network (CSILRR) that consists of 567 interactions. To demonstrate the power of CSILRR for detecting biologically relevant interactions, we predicted and validated the functions of uncharacterized LRR-RKs in plant growth and immunity. In addition, we show that CSILRR operates as a unified regulatory network in which the LRR-RKs most crucial for its overall structure are required to prevent the aberrant signalling of receptors that are several network-steps away. Thus, plants have evolved LRR-RK networks to process extracellular signals into carefully balanced responses.

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New Phytologist: Multiple strategies for pathogen perception by plant immune receptors (2017)

New Phytologist: Multiple strategies for pathogen perception by plant immune receptors (2017) | Plant pathology | Scoop.it

Plants have evolved a complex immune system to protect themselves against phytopathogens. A major class of plant immune receptors called nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs) is ubiquitous in plants and is widely used for crop disease protection, making these proteins critical contributors to global food security. Until recently, NLRs were thought to be conserved in their modular architecture and functional features. Investigation of their biochemical, functional and structural properties has revealed fascinating mechanisms that enable these proteins to perceive a wide range of pathogens. Here, I review recent insights demonstrating that NLRs are more mechanistically and structurally diverse than previously thought. I also discuss how these findings provide exciting future prospects to improve plant disease resistance.


Via Kamoun Lab @ TSL
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Bridget Barker's curator insight, November 21, 2017 2:22 PM
Always thinking about links between animal and plant pathogens
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PLoS Genet: Genomics-enabled analysis of the emergent disease cotton bacterial blight

PLoS Genet: Genomics-enabled analysis of the emergent disease cotton bacterial blight | Plant pathology | Scoop.it

Author summary: Cotton bacterial blight (CBB), caused by Xanthomonas citri pv. malvacearum (Xcm), significantly limited cotton yields in the early 20th century but has been controlled by classical resistance genes for more than 50 years. In 2011, the pathogen re-emerged with a vengeance. In this study, we compare diverse pathogen isolates and cotton varieties to further understand the virulence mechanisms employed by Xcm and to identify promising resistance strategies. We generate fully contiguous genome assemblies for two diverse Xcm strains and identify pathogen proteins used to modulate host transcription and promote susceptibility. RNA-Sequencing of infected cotton reveals novel putative gene targets for the development of durable Xcm resistance. Together, the data presented reveal contributing factors for CBB re-emergence in the U.S. and highlight several promising routes towards the development of durable resistance including classical resistance genes and potential manipulation of susceptibility targets.

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PLoS Pathogens: Dual targeting of a virus movement protein to ER and plasma membrane subdomains is essential for plasmodesmata localization

PLoS Pathogens: Dual targeting of a virus movement protein to ER and plasma membrane subdomains is essential for plasmodesmata localization | Plant pathology | Scoop.it

SUMMARY: Intercellular trafficking of molecules through plasmodesmata (PD) is indispensable for plant development. Plant viruses also use the intercellular trafficking system to establish systemic infection. Virus movement proteins (MPs), which have abilities to localize to PD and to move to the adjacent cells autonomously, play important roles in facilitating virus cell-to-cell movement. Hence, understanding how MPs reach PD has great significance for virology and plant cell biology. In this study, we analyzed the intracellular trafficking of fig mosaic virus movement protein (MPFMV) mainly based on its N-terminal signal peptide (SP). SPs, short peptides directing proteins to the ER, are frequently found in a diverse array of proteins, but rarely found in plant virus proteins. We focused on the SP of MPFMV and investigated the relationship between ER translocation and PD localization. We showed that the SP of MPFMV had quite low translocation efficiency and contributes to generating two distinct populations. Each population localized to specialized subdomains of the ER and PM, and was essential for PD localization, indicating that these subdomains and PD are functionally related. Thus, our findings offer new insights into cell-to-cell movement in plants.

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Frontiers | Stunted growth caused by blast disease in rice seedlings is associated with changes in phytohormone signaling pathways | Plant Science

In response to pathogen attack, plants prioritize defense reactions generally at the expense of plant growth. In this work, we report that changes in phytohormone signaling pathways are associated with the stunted plant growth caused by blast disease in rice seedlings. Infection of rice seedlings with blast fungus Magnaporthe oryzae (race 007.0) at the four-leaf stage (three true leaves) resulted in considerable inhibition of the growth of the upper uninfected distal leaves; the length of leaf blade and leaf sheath of the sixth and seventh leaf was reduced by 27% and 82%, and 88% and 72%, respectively, compared to that in the uninoculated plant control. Interestingly, cutting off the blast-infected fourth leaf within 2 days post inoculation (dpi) significantly rescued the inhibition of leaf growth, implying that an inhibitory substance(s) and/or signal was generated in the blast-infected leaves (fourth leaf) and transmitted to the upper distal leaves (sixth and seventh) during the 2-dpi period that induced growth inhibition. Expression analysis of marker genes for phytohormone pathways revealed acute activation of the jasmonate (JA) and abscisic acid (ABA) signaling pathways, and repression of auxin, gibberellic acid (GA) and salicylic acid (SA) signaling pathways, in the sixth leaf. The genes related to cell wall expansion were also significantly downregulated. In the blast-infected fourth leaf, JA pathway was activated within 2 dpi, followed by activation of ABA pathway 3 dpi. Further, leaf inhibition caused by blast infection was partially rescued in the rice mutant line coleoptile photomorphogenesis 2 (cpm2), which is defective in the gene encoding allene oxide cyclase (OsAOC). These results indicate that the JA signaling pathway is at least partly involved in the growth inhibition processes. Collectively, our data suggest that, upon pathogen attack, rice seedlings prioritize defense reactions against the infecting pathogen by temporarily ceasing plant growth through the systemic control of phytohormone pathways.

Via Philip Carella
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Nat Biotechnol: Rapid cloning of genes in hexaploid wheat using cultivar-specific long-range chromosome assembly

Nat Biotechnol: Rapid cloning of genes in hexaploid wheat using cultivar-specific long-range chromosome assembly | Plant pathology | Scoop.it

ABSTRACT: Cereal crops such as wheat and maize have large repeat-rich genomes that make cloning of individual genes challenging. Moreover, gene order and gene sequences often differ substantially between cultivars of the same crop species 1– 4 . A major bottleneck for gene cloning in cereals is the generation of high-quality sequence information from a cultivar of interest. In order to accelerate gene cloning from any cropping line, we report ‘targeted chromosome-based cloning via long-range assembly’ (TACCA). TACCA combines lossless genome-complexity reduction via chromosome flow sorting with Chicago long-range linkage 5 to assemble complex genomes. We applied TACCA to produce a high-quality (N50 of 9.76 Mb) de novo chromosome assembly of the wheat line CH Campala Lr22a in only 4 months. Using this assembly we cloned the broad-spectrum Lr22a leaf-rust resistance gene, using molecular marker information and ethyl methanesulfonate (EMS) mutants, and found that Lr22a encodes an intracellular immune receptor homologous to the Arabidopsis thaliana RPM1 protein.

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JBC: The Potato Nucleotide-binding Leucine-rich Repeat (NLR) Immune Receptor Rx1 Is a Pathogen-dependent DNA-deforming Protein

ABSTRACT: Plant nucleotide-binding leucine-rich repeat (NLR) proteins enable cells to respond to pathogen attack. Several NLRs act in the nucleus; however, conserved nuclear targets that support their role in immunity are unknown. Previously, we noted a structural homology between the nucleotide-binding domain of NLRs and DNA replication origin-binding Cdc6/Orc1 proteins. Here we show that the NB-ARC (nucleotide-binding, Apaf-1, R-proteins, and CED-4) domain of the Rx1 NLR of potato binds nucleic acids. Rx1 induces ATP-dependent bending and melting of DNA in vitro, dependent upon a functional P-loop. In situ full-length Rx1 binds nuclear DNA following activation by its cognate pathogen-derived effector protein, the coat protein of potato virus X. In line with its obligatory nucleocytoplasmic distribution, DNA binding was only observed when Rx1 was allowed to freely translocate between both compartments and was activated in the cytoplasm. Immune activation induced by an unrelated NLR-effector pair did not trigger an Rx1-DNA interaction. DNA binding is therefore not merely a consequence of immune activation. These data establish a role for DNA distortion in Rx1 immune signaling and define DNA as a molecular target of an activated NLR.
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PNAS: Pathogen exploitation of an abscisic acid- and jasmonate-inducible MAPK phosphatase and its interception by Arabidopsis immunity

SIGNIFICANCE: Pathogens cause disease by deploying virulence effectors that interfere with various host targets, whereas plants counteract pathogen virulence when invoking a potent immunity known as effector-triggered immunity (ETI). Little is known about the mechanism underlying this molecular battle between plant immunity and pathogen virulence. We find that the phytohormones abscisic acid and jasmonate (JA), the signaling pathways of which are often exploited by pathogens, transcriptionally activate a common family of protein phosphatases that suppress immune-associated MAP kinases. We demonstrate that a bacterial pathogen exploits the JA-mediated suppression of MAP kinases by using a JA-mimic, whereas ETI blocks JA signaling to counteract this bacterial virulence. Our results highlight suppression and protection of MAP kinases as a molecular battle between pathogens and plants.

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Current Opinion Plant Biology: Extracellular vesicles as key mediators of plant–microbe interactions (2018)

Current Opinion Plant Biology: Extracellular vesicles as key mediators of plant–microbe interactions (2018) | Plant pathology | Scoop.it
• Plants produce extracellular vesicles (EVs) in response to infection.• Recent advances in EV purification are now revealing the contents of plant EVs.• Plant EVs are enriched in stress-response proteins and signaling lipids.• EVs contain transporters for antimicrobial compounds such as glucosinolates.• Indirect evidence suggests that EVs may mediate inter-kingdom RNA interference.

Extracellular vesicles (EVs) are lipid compartments capable of trafficking proteins, lipids, RNA and metabolites between cells. Plant cells have been shown to secrete EVs during immune responses, but virtually nothing is known about their formation, contents or ultimate function. Recently developed methods for isolating plant EVs have revealed that these EVs are enriched in stress response proteins and signaling lipids, and appear to display antifungal activity. Comparison to work on animal EVs, and the observation that host-derived small interfering RNAs and microRNAs can silence fungal genes, suggests that plant EVs may also mediate trans-kingdom RNA interference. Many fundamental questions remain, however, regarding how plant EVs are produced, how they move, and if and how they are taken up by target cells.


Via Kamoun Lab @ TSL
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Nat Genet: Bph6 encodes an exocyst - localized protein and confers broad resistance to planthoppers in rice

Nat Genet: Bph6 encodes an exocyst - localized protein and confers broad resistance to planthoppers in rice | Plant pathology | Scoop.it

ABSTRACT: The brown planthopper (BPH) and white-backed planthopper (WBPH) are the most destructive insect pests of rice, and they pose serious threats to rice production throughout Asia. Thus, there are urgent needs to identify resistance-conferring genes and to breed planthopper-resistant rice varieties. Here we report the map-based cloning and functional analysis of Bph6 , a gene that confers resistance to planthoppers in rice. Bph6 encodes a previously uncharacterized protein that localizes to exo- cysts and interacts with the exocyst subunit OsEXO70E1. Bph6 expression increases exocytosis and participates in cell wall maintenance and reinforcement. A coordinated cytokinin, salicylic acid and jasmonic acid signaling pathway is activated in Bph6 -carrying plants, which display broad resistance to all tested BPH biotypes and to WBPH without sacrificing yield, as these plants were found to maintain a high level of performance in a field that was heavily infested with BPH. Our results suggest that a superior resistance gene that evolved long ago in a region where planthoppers are found year round could be very valuable for controlling agricultural insect pests.

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Nat Plants: An apoplastic peptide activates salicylic acid signalling in maize

Nat Plants: An apoplastic peptide activates salicylic acid signalling in maize | Plant pathology | Scoop.it

ABSTRACT: Localized control of cell death is crucial for the resistance of plants to pathogens. Papain-like cysteine proteases (PLCPs) regulate plant defence to drive cell death and protection against biotrophic pathogens. In maize (Zea mays), PLCPs are crucial in the orchestration of salicylic acid (SA)-dependent defence signalling. Despite this central role in immunity, it remains unknown how PLCPs are activated, and which downstream signals they induce to trigger plant immunity. Here, we discover an immune signalling peptide, Z. mays immune signalling peptide 1 (Zip1), which is produced after salicylic acid (SA) treatment. In vitro studies demonstrate that PLCPs are required to release bioactive Zip1 from its propeptide precursor. Conversely, Zip1 treatment strongly elicits SA accumulation in leaves. Moreover, transcriptome analyses revealed that Zip1 and SA induce highly overlapping transcriptional changes. Consequently, Zip1 promotes the infection of the necrotrophic fungus Botrytis cinerea, while it reduces virulence of the biotrophic fungus Ustilago maydis. Thus, Zip1 represents the previously missing signal that is released by PLCPs to activate SA defence signalling.

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BMC Microbiol: Classification of a new phytoplasmas subgroup 16SrII-W associated with Crotalaria witches’ broom diseases in Oman based on multigene sequence analysis


Crotalaria aegyptiaca, a low shrub is commonly observed in the sandy soils of wadis desert and is found throughout all regions in Oman. A survey for phytoplasma diseases was conducted. During a survey in a wild area in the northern regions of Oman in 2015, typical symptoms of phytoplasma infection were observed on C. aegyptiaca plants. The infected plants showed an excessive proliferation of their shoots and small leaves. The presence of phytoplasma in the phloem tissue of symptomatic C. aegyptiaca leaf samples was confirmed by using Transmission Electron Microscopy (TEM). In addition the extracted DNA from symptomatic C. aegyptiaca leaf samples and Orosius sp. leafhoppers were tested by PCR using phytoplasma specific primers for the 16S rDNA, secA, tuf and imp, and SAP11 genes. The PCR amplifications from all samples yielded the expected products, but not from asymptomatic plant samples. Sequence similarity and phylogenetic tree analyses of four genes (16S rDNA, secA, tuf and imp) showed that Crotalaria witches’ broom phytoplasmas from Oman is placed with the clade of Peanut WB (16SrII) close to Fava bean phyllody (16SrII-C), Cotton phyllody and phytoplasmas (16SrII-F), and Candidatus Phytoplasma aurantifolia’ (16SrII-B). However, the Crotalaria’s phytoplasma was in a separate sub-clade from all the other phytoplasmas belonging to Peanut WB group. The combination of specific primers for the SAP11 gene of 16SrII-A, −B, and -D subgroup pytoplasmas were tested against Crotalaria witches’ broom phytoplasmas and no PCR product was amplified, which suggests that the SAP11 of Crotalaria phytoplasma is different from the SAP11 of the other phytoplasmas. We propose to assign the Crotalaria witches’ broom from Oman in a new lineage 16SrII-W subgroup depending on the sequences analysis of 16S rRNA, secA, imp, tuf, and SAP11 genes. To our knowledge, this is the first report of phytoplasmas of the 16SrII group infecting C. aegyptiaca worldwide.
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The quest for durable resistance

The quest for durable resistance | Plant pathology | Scoop.it
Agriculture transformed humans from hunter-gatherers into city dwellers. This was made possible through the domestication of crops, such as wheat and barley. Based on archaeological evidence ( 1 ), we know that our ancestors' crops were constantly plagued by disease, including rusts and mildews on cereals. During the 4th century BCE, Romans sacrificed red cattle, foxes, and dogs to the god Robigus in the belief that it would prevent epidemics of cereal rusts. Today, we understand that crop diseases are caused by plant pathogens. Cereal rusts are fungal pathogens that colonize foliar parts of the plant, such as the stem or leaf. The ability of these pathogens to infect a plant requires the suppression of the plant's immune system. The principal weapon used by pathogens to inhibit immunity are effectors, typically small secreted proteins. Plants recognize pathogens through immune receptors, including those that either directly or indirectly “perceive” pathogen effectors secreted into the plant ( 2 ). On pages 1604 and 1607 of this issue, Salcedo et al. ( 3 ) and Chen et al. ( 4 ), respectively, describe the identification of two effectors from the fungal pathogen Puccinia graminis f. sp. tritici , the causal agent of wheat stem rust. The discovery of these effectors represents a critical milestone for developing an approach to track and prevent the worldwide spread of the rusts of wheat ( 5 ) and improve our understanding of the biology of these devastating pathogens.

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MPMI: Lessons in Effector and NLR Biology of Plant-Microbe Systems (2017)

MPMI: Lessons in Effector and NLR Biology of Plant-Microbe Systems (2017) | Plant pathology | Scoop.it

A diversity of plant-associated organisms secrete effectors—proteins and metabolites that modulate plant physiology to favor host infection and colonization. However, effectors can also activate plant immune receptors, notably nucleotide-binding domain and leucine-rich repeat region (NLR)-containing proteins, enabling plants to fight off invading organisms. This interplay between effectors, their host targets, and the matching immune receptors is shaped by intricate molecular mechanisms and exceptionally dynamic coevolution. In this article, we focus on three effectors, AVR-Pik, AVR-Pia, and AVR-Pii, from the rice blast fungus Magnaporthe oryzae (syn. Pyricularia oryzae), and their corresponding rice NLR immune receptors, Pik, Pia, and Pii, to highlight general concepts of plant-microbe interactions. We draw 12 lessons in effector and NLR biology that have emerged from studying these three little effectors and are broadly applicable to other plant-microbe systems.


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MPMI: The bacterial effector AvrPto targets the regulatory co-receptor SOBIR1 and suppresses defence signalling mediated by the receptor-like protein Cf-4

ABSTRACT: Receptor-like proteins (RLPs) and receptor-like kinases (RLKs) are cell surface receptors that are essential for detecting invading pathogens and subsequent activation of plant defence responses. RLPs lack a cytoplasmic kinase domain to trigger downstream signalling leading to host resistance. The RLK SOBIR1 constitutively interacts with the tomato RLP Cf-4, thereby providing Cf-4 with a kinase domain. SOBIR1 is required for Cf-4-mediated resistance to strains of the fungal tomato pathogen Cladosporium fulvum that secrete the effector Avr4. Upon perception of this effector by the Cf-4/SOBIR1 complex, the central regulatory RLK SERK3a is recruited to the complex and defence signalling is triggered. SOBIR1 is also required for RLP-mediated resistance to bacterial, fungal and oomycete pathogens and we hypothesized that SOBIR1 is targeted by effectors of such pathogens to suppress host defence responses. In this study we show that Pseudomonas syringae pv. tomato DC3000 effector AvrPto interacts with Arabidopsis SOBIR1 and its orthologs of tomato and Nicotiana benthamiana, independent of SOBIR1 kinase activity. Interestingly, AvrPto suppresses Arabidopsis SOBIR1-induced cell death in N. benthamiana. Furthermore, AvrPto compromises Avr4-triggered cell death in Cf-4-transgenic N. benthamiana, without affecting Cf-4/SOBIR1/SERK3a complex formation. Our study shows that the RLP co-receptor SOBIR1 is targeted by a bacterial effector, which results in compromised defence responses.
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細胞死ちゃんとはからないの
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PLoS ONE: A time series transcriptome analysis of cassava ( Manihot esculenta Crantz) varieties challenged with Ugandan cassava brown streak virus

PLoS ONE: A time series transcriptome analysis of cassava ( Manihot esculenta Crantz) varieties challenged with Ugandan cassava brown streak virus | Plant pathology | Scoop.it

ABSTRACT:A time-course transcriptome analysis of two cassava varieties that are either resistant or susceptible to cassava brown streak disease (CBSD) was conducted using RNASeq, after graft inoculation with Ugandan cassava brown streak virus (UCBSV). From approximately 1.92 billion short reads, the largest number of differentially expressed genes (DEGs) was obtained in the resistant (Namikonga) variety at 2 days after grafting (dag) (3887 DEGs) and 5 dag (4911 DEGs). At the same time points, several defense response genes (encoding LRR-containing, NBARC-containing, pathogenesis-related, late embryogenesis abundant, selected transcription factors, chaperones, and heat shock proteins) were highly expressed in Namikonga. Also, defense-related GO terms of ‘translational elongation’, ‘translation factor activity’, ‘ribosomal subunit’ and ‘phosphorelay signal transduction’, were overrepresented in Namikonga at these time points. More reads corresponding to UCBSV sequences were recovered from the susceptible variety (Albert) (733 and 1660 read counts per million (cpm)) at 45 dag and 54 dag compared to Namikonga (10 and 117 cpm respectively). These findings suggest that Namikonga’s resistance involves restriction of multiplication of UCBSV within the host. These findings can be used with other sources of evidence to identify candidate genes and biomarkers that would contribute substantially to knowledge-based resistance breeding.

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PNAS: NLR network mediates immunity to diverse plant pathogens (2017)

PNAS: NLR network mediates immunity to diverse plant pathogens (2017) | Plant pathology | Scoop.it

Both plants and animals rely on nucleotide-binding domain and leucine-rich repeat-containing (NLR) proteins to respond to invading pathogens and activate immune responses. An emerging concept of NLR function is that “sensor” NLR proteins are paired with “helper” NLRs to mediate immune signaling. However, our fundamental knowledge of sensor/helper NLRs in plants remains limited. In this study, we discovered a complex NLR immune network in which helper NLRs in the NRC (NLR required for cell death) family are functionally redundant but display distinct specificities toward different sensor NLRs that confer immunity to oomycetes, bacteria, viruses, nematodes, and insects. The helper NLR NRC4 is required for the function of several sensor NLRs, including Rpi-blb2, Mi-1.2, and R1, whereas NRC2 and NRC3 are required for the function of the sensor NLR Prf. Interestingly, NRC2, NRC3, and NRC4 redundantly contribute to the immunity mediated by other sensor NLRs, including Rx, Bs2, R8, and Sw5. NRC family and NRC-dependent NLRs are phylogenetically related and cluster into a well-supported superclade. Using extensive phylogenetic analysis, we discovered that the NRC superclade probably emerged over 100 Mya from an NLR pair that diversified to constitute up to one-half of the NLRs of asterids. These findings reveal a complex genetic network of NLRs and point to a link between evolutionary history and the mechanism of immune signaling. We propose that this NLR network increases the robustness of immune signaling to counteract rapidly evolving plant pathogens.


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Do Endophytes Promote Growth of Host Plants Under Stress? A Meta-Analysis on Plant Stress Mitigation by Endophytes

Endophytes are microbial symbionts living inside plants and have been extensively researched in recent decades for their functions associated with plant responses to environmental stress. We conducted a meta-analysis of endophyte effects on host plants’ growth and fitness in response to three abiotic stress factors: drought, nitrogen deficiency, and excessive salinity. Ninety-four endophyte strains and 42 host plant species from the literature were evaluated in the analysis. Endophytes increased biomass accumulation of host plants under all three stress conditions. The stress mitigation effects by endophytes were similar among different plant taxa or functional groups with few exceptions; eudicots and C4 species gained more biomass than monocots and C3 species with endophytes, respectively, under drought conditions. Our analysis supports the effectiveness of endophytes in mitigating drought, nitrogen deficiency, and salinity stress in a wide range of host species with little evidence of plant-endophyte specificity.


Via Jean-Michel Ané
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WillistonPlantPath's curator insight, September 5, 2017 9:47 PM
More evidence to promote the importance of the plant associated microbiome!
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Ann Rev Phytopathol: Ecology and Genomic Insights into Plant-Pathogenic and Plant-Nonpathogenic Endophytes |

ABSTRACT: Plants are colonized on their surfaces and in the rhizosphere and phyllosphere by a multitude of different microorganisms and are inhabited internally by endophytes. Most endophytes act as commensals without any known effect on their plant host, but multiple bacteria and fungi establish a mutualistic relationship with plants, and some act as pathogens. The outcome of these plant-microbe interactions depends on biotic and abiotic environmental factors and on the genotype of the host and the interacting microorganism. In addition, endophytic microbiota and the manifold interactions between members, including pathogens, have a profound influence on the function of the system plant and the development of pathobiomes. In this review, we elaborate on the differences and similarities between nonpathogenic and pathogenic endophytes in terms of host plant response, colonization strategy, and genome content. We furthermore discuss environmental effects and biotic interactions within plant microbiota that influence pathogenesis and the pathobiome.


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BMC Evol and Biol: Plant manipulation through gall formation constrains amino acid transporter evolution in sap-feeding insects

The herbivore lifestyle leads to encounters with plant toxins and requires mechanisms to overcome suboptimal nutrient availability in plant tissues. Although the evolution of bacterial endosymbiosis alleviated many of these challenges, the ability to manipulate plant nutrient status has evolved in lineages with and without nutritional symbionts. Whether and how these alternative nutrient acquisition strategies interact or constrain insect evolution is unknown. We studied the transcriptomes of galling and free-living aphidomorphs to characterize how amino acid transporter evolution is influenced by the ability to manipulate plant resource availability. Using a comparative approach we found phylloxerids retain nearly all amino acid transporters as other aphidomorphs, despite loss of nutritional endosymbiosis. Free living species show more transporters than galling species within the same genus, family, or infraorder, indicating plant hosts influence the maintenance and evolution of nutrient transport within herbivores. Transcript profiles also show lineage specificity and suggest some genes may facilitate life without endosymbionts or the galling lifestyle. The transcript abundance profiles we document across fluid feeding herbivores support plant host constraint on insect amino acid transporter evolution. Given amino acid uptake, transport, and catabolism underlie the success of herbivory as a life history strategy, this suggests that plant host nutrient quality, whether constitutive or induced, alters the selective environment surrounding the evolution and maintenance of endosymbiosis.
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