Fungal-plant interactions
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A fungal avirulence factor encoded in a highly plastic genomic region triggers partial resistance to septoria tritici blotch

A fungal avirulence factor encoded in a highly plastic genomic region triggers partial resistance to septoria tritici blotch | Fungal-plant interactions | Scoop.it
Cultivar‐strain specificity in the wheat–Zymoseptoria tritici pathosystem determines the infection outcome and is controlled by resistance genes on the host side, many of which have been identified. On the pathogen side, however, the molecular determinants of specificity remain largely unknown.
We used genetic mapping, targeted gene disruption and allele swapping to characterise the recognition of the new avirulence factor Avr3D1. We then combined population genetic and comparative genomic analyses to characterise the evolutionary trajectory of Avr3D1. 
Avr3D1 is specifically recognised by wheat cultivars harbouring the Stb7 resistance gene, triggering a strong defence response without preventing pathogen infection and reproduction. Avr3D1 resides in a cluster of putative effector genes located in a genome region populated by independent transposable element insertions. The gene was present in all 132 investigated strains and is highly polymorphic, with 30 different protein variants identified. We demonstrated that specific amino acid substitutions in Avr3D1 led to evasion of recognition. 
These results demonstrate that quantitative resistance and gene‐for‐gene interactions are not mutually exclusive. Localising avirulence genes in highly plastic genomic regions probably facilitates accelerated evolution that enables escape from recognition by resistance proteins. 
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Extracellular Vesicle RNA: A Universal Mediator of Microbial Communication?

Extracellular Vesicle RNA: A Universal Mediator of Microbial Communication? | Fungal-plant interactions | Scoop.it
Both extracellular RNAs and extracellular vesicles (EVs) have recently garnered attention as novel mediators of intercellular communication in eukaryotes and prokaryotes alike. EVs not only permit export of RNA, but also facilitate delivery and trans-kingdom exchange of these and other biomolecules, for instance between microbes and their hosts. In this Opinion article, we propose that EV-mediated export of RNA represents a universal mechanism for interkingdom and intrakingdom communication that is conserved among bacterial, archaeal, and eukaryotic microbes. We speculate how microbes might use EV RNA to influence target cell gene expression or manipulate host immune responses.

Via Jonathan Plett, Francis Martin, IPM Lab
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Beclin1 restricts RNA virus infection in plants through suppression and degradation of the viral polymerase

Beclin1 restricts RNA virus infection in plants through suppression and degradation of the viral polymerase | Fungal-plant interactions | Scoop.it
Autophagy emerges as an essential immunity defense against intracellular pathogens. Here we report that turnip mosaic virus (TuMV) infection activates autophagy in plants and that Beclin1 (ATG6), a core component of autophagy, inhibits virus replication. Beclin1 interacts with NIb, the RNA-dependent RNA polymerase (RdRp) of TuMV, via the highly conserved GDD motif and the interaction complex is targeted for autophagic degradation likely through the adaptor protein ATG8a. Beclin1-mediated NIb degradation is inhibited by autophagy inhibitors. Deficiency of Beclin1 or ATG8a enhances NIb accumulation and promotes viral infection and vice versa. These data suggest that Beclin1 may be a selective autophagy receptor. Overexpression of a Beclin1 truncation mutant that binds to NIb but lacks the ability to mediate NIb degradation also inhibits virus replication. The Beclin1–RdRp interaction further extends to several RNA viruses. Thus Beclin1 restricts viral infection through suppression and also likely autophagic degradation of the viral RdRp.

Via Suayib Üstün
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PLOS Pathogens: Tricked or trapped—Two decoy mechanisms in host–pathogen interactions (2018)

PLOS Pathogens: Tricked or trapped—Two decoy mechanisms in host–pathogen interactions (2018) | Fungal-plant interactions | Scoop.it

Antagonistic interactions between hosts and pathogens frequently result in arms races. The host attempts to recognise the pathogen and inhibit its growth and spread, whereas the pathogen tries to subvert recognition and suppress host responses. These antagonistic interactions drive the evolution of ‘decoys’ in both hosts and pathogens. In host–pathogen interactions, the term decoy describes molecules that mimic a component at the host–pathogen interface that is manipulated during infection. Decoys undergo the same manipulation as the component they mimic, but they serve the opposite role, either by preventing manipulation of the component they mimic or by triggering a molecular recognition event. At least three different types of decoy have been defined, described in detail below. However, these different decoy models cause confusion on how they function mechanistically. Here, we discuss the three different types of decoys with examples and classify them according to two distinct mechanisms.


Via Kamoun Lab @ TSL
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Leucine-rich repeat receptor-like gene screen reveals that Nicotiana RXEG1 regulates glycoside hydrolase 12 MAMP detection

Leucine-rich repeat receptor-like gene screen reveals that Nicotiana RXEG1 regulates glycoside hydrolase 12 MAMP detection | Fungal-plant interactions | Scoop.it

Activation of innate immunity by membrane-localized receptors is conserved across eukaryotes. Plant genomes contain hundreds of such receptor-like genes and those encoding proteins with an extracellular leucine-rich repeat (LRR) domain represent the largest family. Here, we develop a high-throughput approach to study LRR receptor-like genes on a genome-wide scale. In total, 257 tobacco rattle virus-based constructs are generated to target 386 of the 403 identified LRR receptor-like genes in Nicotiana benthamiana for silencing. Using this toolkit, we identify the LRR receptor-like protein Response to XEG1 (RXEG1) that specifically recognizes the glycoside hydrolase 12 protein XEG1. RXEG1 associates with XEG1 via the LRR domain in the apoplast and forms a complex with the LRR receptor-like kinases BAK1 and SOBIR1 to transduce the XEG1-induced defense signal. Thus, this genome-wide silencing assay is demonstrated to be an efficient toolkit to pinpoint new immune receptors, which will contribute to developing durable disease resistance.

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Plant cell wall‐mediated immunity: cell wall changes trigger disease resistance responses

Plant cell wall‐mediated immunity: cell wall changes trigger disease resistance responses | Fungal-plant interactions | Scoop.it

Plants have evolutionary developed a repertoire of monitoring systems to sense plant morphogenesis and to face environmental changes and threats caused by different attackers. These systems integrate different signals into overreaching triggering pathways, which coordinate developmental and defensive-associated responses. The plant cell wall, a dynamic and complex structure surrounding every plant cell, has emerged recently as an essential component of plant monitoring systems, thus expanding its function as a passive defensive barrier. Plants have a dedicated cell wall integrity (CWI) maintenance mechanism which comprises a diverse set of plasma membrane-resident sensors and Pattern Recognition Receptors (PRRs). PRRs perceive plant-derived ligands, such as peptides or wall glycans, known as Damage-Associated Molecular Patterns (DAMPs). DAMPs function as “danger” alert signals activating DAMP-Triggered Immunity (DTI), which shares signalling components and responses with the immune pathways triggered by non-self Microbe-Associated Molecular Patterns that mediate disease resistance. Alteration of CWI by impairing the expression or activity of proteins involved in cell wall biosynthesis and/or remodelling, as it occurs in some plant cell wall mutants, or by wall damages caused by pathogens/pests colonization, activate specific defensive and growth responses. Our current understanding of how these alterations of CWI are perceived by the wall monitoring systems is scarce and few plant sensors/PRRs and DAMPs have been characterised. The identification of these CWI sensors and PRRs-DAMPs pairs will contribute to understand the immune functions of the wall monitoring system, and might allow to breed crop varieties and to design agricultural strategies that would enhance crops disease resistance.

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Plant Cell: Defended to the Nines: 25 years of Resistance Gene Cloning Identifies Nine Mechanisms for R Protein Function (2018)

Plant Cell: Defended to the Nines: 25 years of Resistance Gene Cloning Identifies Nine Mechanisms for R Protein Function (2018) | Fungal-plant interactions | Scoop.it

Plants display extensive genetic variation at resistance (R) gene loci for resistance to a variety of pathogens. The first R gene, Hm1, was cloned over 25 years ago, and many different R genes have since been identified and isolated. The encoded proteins have provided clues to diverse molecular mechanisms underlying immunity. The majority encode either cell-surface or intracellular receptors, and we present here a meta- analysis of 314 cloned R genes. We distinguish nine molecular mechanisms by which R proteins can elevate or trigger disease resistance. These mechanisms include direct (1) and indirect (2) perception of pathogen-derived molecules on the cell surface by receptor-like proteins and -kinases; intracellular detection of pathogen-derived molecules by nucleotide-binding, leucine-rich repeat receptors (NLRs), either directly (3), indirectly (4) or through integrated domains (5); perception of Transcription Activator-like (TAL) effectors through activation of Executor genes (6); and loss-of-susceptibility, either active (7), passive (8), or by host reprogramming (9). Although the molecular mechanisms underlying the function of R genes are only understood for a small proportion of these, a clearer understanding of mechanisms is emerging and will be crucial for rational engineering and deployment of novel R genes.


Via Kamoun Lab @ TSL
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Top20 plant pathology papers published in 2017: my unconsciously biased selection

Eudicot plant-specific sphingolipids determine host selectivity of microbial NLP cytolysins
http://science.sciencemag.org/content/358/6369/1431

The receptor kinase FER is a RALF-regulated scaffold controlling plant immune signaling
http://science.sciencemag.org/content/355/6322/287

TIR-only protein RBA1 recognizes a pathogen effector to regulate cell death in Arabidopsis
http://www.pnas.org/content/114/10/E2053.long

Improvement of multiple agronomic traits by a disease resistance gene via cell wall reinforcement
https://www.nature.com/articles/nplants20179

The RxLR motif of the host targeting effector AVR3a of Phytophthora infestans is cleaved before secretion
http://www.plantcell.org/content/early/2017/05/18/tpc.16.00552

Evolution of the wheat blast fungus through functional losses in a host specificity determinant
http://science.sciencemag.org/content/357/6346/80.long

NLR network mediates immunity to diverse plant pathogens http://www.pnas.org/content/114/30/8113

The pattern-recognition receptor CORE of Solanaceae detects bacterial cold-shock protein
https://www.nature.com/articles/nplants2016185

Disease resistance through impairment of α-SNAP–NSF interaction and vesicular trafficking by soybean Rhg1
http://www.pnas.org/content/113/47/E7375.long

A natural allele of a transcription factor in rice confers broad-spectrum blast resistance
http://www.cell.com/cell/fulltext/S0092-8674(17)30649-9

Delivery of cytoplasmic and apoplastic effectors from Phytophthora infestans haustoria by distinct secretion pathways http://onlinelibrary.wiley.com/doi/10.1111/nph.14696/full

A plant effector‐triggered immunity signaling sector is inhibited by pattern‐triggered immunity
http://emboj.embopress.org/content/early/2017/08/15/embj.201796529

A gene encoding maize caffeoyl-CoA O-methyltransferase confers quantitative resistance to multiple pathogens https://www.nature.com/articles/ng.3919

Differential regulation of two-tiered plant immunity and sexual reproduction by ANXUR receptor-like kinase
http://www.plantcell.org/content/early/2017/11/17/tpc.17.00464

A bacterial type III effector targets the master regulator of salicylic acid signaling, NPR1, to subvert plant immunity
http://www.cell.com/cell-host-microbe/fulltext/S1931-3128(17)30454-7

Host-mediated S-nitrosylation disarms the bacterial effector HopAI1 to re-establish immunity
http://www.plantcell.org/content/29/11/2871

A 1-phytase type III effector interferes with plant hormone signaling https://www.nature.com/articles/s41467-017-02195-8

Plants transfer lipids to sustain colonization by mutualistic mycorrhizal and parasitic fungi
http://science.sciencemag.org/content/early/2017/06/07/science.aam9970

Plant immune and growth receptors share common signalling components but localise to distinct plasma membrane nanodomains https://elifesciences.org/articles/25114

A Phytophthora effector manipulates host histone acetylation and reprograms defense gene expression to promote infection http://www.cell.com/current-biology/fulltext/S0960-9822(17)30214-2
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Extensive gene content variation in the Brachypodium distachyon pan-genome correlates with population structure

Extensive gene content variation in the Brachypodium distachyon pan-genome correlates with population structure | Fungal-plant interactions | Scoop.it

While prokaryotic pan-genomes have been shown to contain many more genes than any individual organism, the prevalence and functional significance of differentially present genes in eukaryotes remains poorly understood. Whole-genome de novo assembly and annotation of 54 lines of the grass Brachypodium distachyon yield a pan-genome containing nearly twice the number of genes found in any individual genome. Genes present in all lines are enriched for essential biological functions, while genes present in only some lines are enriched for conditionally beneficial functions (e.g., defense and development), display faster evolutionary rates, lie closer to transposable elements and are less likely to be syntenic with orthologous genes in other grasses. Our data suggest that differentially present genes contribute substantially to phenotypic variation within a eukaryote species, these genes have a major influence in population genetics, and transposable elements play a key role in pan-genome evolution.

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Review on resistance to wheat blast disease (Magnaporthe oryzae Triticum) from the breeder point-of-view: use of the experience on resistance to rice blast disease

Review on resistance to wheat blast disease (Magnaporthe oryzae Triticum) from the breeder point-of-view: use of the experience on resistance to rice blast disease | Fungal-plant interactions | Scoop.it

This review on the resistance to wheat blast disease focus on the latest knowledge useful for the breeders, but also takes into account the lacks in these knowledge. To tackle this disease, it is relevant to apply a breeding strategy which has previously proven its efficacy for obtaining rice varieties with a high level of partial and durable resistance to blast. But, incomplete information is available on wheat blast resistance. Therefore, firstly, it is necessary to adjust this breeding strategy considering the worst hypothesis corresponding to every lack of knowledge. Next, the possible invalidation of every hypothesis can allow simplifying the breeding schema and its implementation. For every lack of knowledge, the practical consequences of the corresponding worst hypothesis, the study of its validity and the consequences of its possible invalidation are explained. Scientific arguments, materials and methods details are provided with the latest available references.

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The quest for durable resistance

The quest for durable resistance | Fungal-plant interactions | 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.

Via Francis Martin
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Variation in the AvrSr35 gene determines Sr35 resistance against wheat stem rust race Ug99

Variation in the AvrSr35 gene determines Sr35 resistance against wheat stem rust race Ug99 | Fungal-plant interactions | Scoop.it
Puccinia graminis f. sp. tritici (Pgt) causes wheat stem rust, a devastating fungal disease. The Sr35 resistance gene confers immunity against this pathogen’s most virulent races, including Ug99. We used comparative whole-genome sequencing of chemically mutagenized and natural Pgt isolates to identify a fungal gene named AvrSr35 that is required for Sr35 avirulence. The AvrSr35 gene encodes a secreted protein capable of interacting with Sr35 and triggering the immune response. We show that the origin of Pgt isolates virulent on Sr35 is associated with the nonfunctionalization of the AvrSr35 gene by the insertion of a mobile element. The discovery of AvrSr35 provides a new tool for Pgt surveillance, identification of host susceptibility targets, and characterization of the molecular determinants of immunity in wheat.

Via Francis Martin
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Frontiers: Effector proteins of rust fungi (2014)

Frontiers: Effector proteins of rust fungi (2014) | Fungal-plant interactions | Scoop.it

Rust fungi include many species that are devastating crop pathogens. To develop resistant plants, a better understanding of rust virulence factors, or effector proteins, is needed. Thus far, only six rust effector proteins have been described: AvrP123, AvrP4, AvrL567, AvrM, RTP1 and PGTAUSPE-10-1. Although some are well established model proteins used to investigate mechanisms of immune receptor activation (avirulence activities) or entry into plant cells, how they work inside host tissues to promote fungal growth remains unknown. The genome sequences of four rust fungi (two Melampsoraceae and two Pucciniaceae) have been analyzed so far. Genome-wide analyses of these species, as well as transcriptomics performed on a broader range of rust fungi, revealed hundreds of small secreted proteins considered as rust candidate secreted effector proteins (CSEPs). The rust community now needs high-throughput approaches (effectoromics) to accelerate effector discovery/characterization and to better understand how they function in planta. However, this task is challenging due to the non-amenability of rust pathosystems (obligate biotrophs infecting crop plants) to traditional molecular genetic approaches mainly due to difficulties in culturing these species in vitro. The use of heterologous approaches should be promoted in the future.


Via Kamoun Lab @ TSL
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The Ustilago maydis repetitive effector Rsp3 blocks the antifungal activity of mannose-binding maize proteins

The Ustilago maydis repetitive effector Rsp3 blocks the antifungal activity of mannose-binding maize proteins | Fungal-plant interactions | Scoop.it

To cause disease in maize, the biotrophic fungus Ustilago maydis secretes a large arsenal of effector proteins. Here, we functionally characterize the repetitive effector Rsp3 (repetitive secreted protein 3), which shows length polymorphisms in field isolates and is highly expressed during biotrophic stages. Rsp3 is required for virulence and anthocyanin accumulation. During biotrophic growth, Rsp3 decorates the hyphal surface and interacts with at least two secreted maize DUF26-domain family proteins (designated AFP1 and AFP2). AFP1 binds mannose and displays antifungal activity against the rsp3 mutant but not against a strain constitutively expressing rsp3. Maize plants silenced for AFP1 and AFP2 partially rescue the virulence defect of rsp3 mutants, suggesting that blocking the antifungal activity of AFP1 and AFP2 by the Rsp3 effector is an important virulence function. Rsp3 orthologs are present in all sequenced smut fungi, and the ortholog from Sporisorium reilianum can complement the rsp3 mutant of U. maydis, suggesting a novel widespread fungal protection mechanism.

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The bacterial type III-secreted protein AvrRps4 is a bipartite effector

The bacterial type III-secreted protein AvrRps4 is a bipartite effector | Fungal-plant interactions | Scoop.it

An important component of the plant immune system relies on the detection of pathogen-derived effectors by immune receptors called resistance proteins. Bacterial pathogens inject effectors into the host cell via a dedicated secretion system to suppress defenses and to manipulate the physiology of the host cell to the pathogen's advantage. Usually, a single resistance protein recognizes a single effector, but an increasing number of exceptions and elaborations on this one-to-one relationship are known. The plant Arabidopsis uses a pair of resistance proteins, RRS1 and RPS4, to detect the effector AvrRps4. After injection into the cell, AvrRps4 is cleaved into two protein parts, and it had been assumed that only the C-terminal part needs to be present to trigger RPS4/RRS1. We show here that both AvrRps4 parts are required for triggering resistance in Arabidopsis, and that the N-terminal part, which previously had been assumed to only function in effector secretion into the host cell, in fact on its own has some functions of an effector. This conclusion is supported by the observation that the N-terminal part of AvrRps4 is sufficient to trigger resistance in lettuce. The fusion of the two AvrRps4 parts may have arisen to counteract plant defenses.

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Leptosphaeria maculans AvrLm9: a new player in the game of hide and seek with AvrLm4-7 - Ghanbarnia - 2018 - Molecular Plant Pathology - Wiley Online Library

Leptosphaeria maculans AvrLm9: a new player in the game of hide and seek with AvrLm4-7 - Ghanbarnia - 2018 - Molecular Plant Pathology - Wiley Online Library | Fungal-plant interactions | Scoop.it

Blackleg disease of Brassica napus caused by Leptosphaeria maculans (Lm) is largely controlled by the deployment of race-specific resistance (R) genes. However, selection pressure exerted by R genes causes Lm to adapt and give rise to new virulent strains through mutation and deletion of effector genes. Therefore, a knowledge of effector gene function is necessary for the effective management of the disease. Here, we report the cloning of Lm effector AvrLm9 which is recognized by the resistance gene Rlm9 in B. napus cultivar Goéland. AvrLm9 was mapped to scaffold 7 of the Lm genome, co-segregating with the previously reported AvrLm5 (previously known as AvrLmJ1). Comparison of AvrLm5 alleles amongst the 37 re-sequenced Lm isolates and transgenic complementation identified a single point mutation correlating with the AvrLm9 phenotype. Therefore, we renamed this gene as AvrLm5-9 to reflect the dual specificity of this locus. Avrlm5-9 transgenic isolates were avirulent when inoculated on the B. napus cultivar Goéland. The expression of AvrLm5-9 during infection was monitored by RNA sequencing. The recognition of AvrLm5-9 by Rlm9 is masked in the presence of AvrLm4-7, another Lm effector. AvrLm5-9 and AvrLm4-7 do not interact, and AvrLm5-9 is expressed in the presence of AvrLm4-7. AvrLm5-9 is the second Lm effector for which host recognition is masked by AvrLm4-7. An understanding of this complex interaction will provide new opportunities for the engineering of broad-spectrum recognition.

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Host-induced gene silencing of a regulator of G protein signaling gene (VdRGS1) confers resistance to Verticillium wilt in cotton - Xu - 2018 - Plant Biotechnology Journal - Wiley Online Library

Host-induced gene silencing of a regulator of G protein signaling gene (VdRGS1) confers resistance to Verticillium wilt in cotton - Xu - 2018 - Plant Biotechnology Journal - Wiley Online Library | Fungal-plant interactions | Scoop.it

"Verticillium wilt (VW), caused by soil-borne fungi of the genus Verticillium, is a serious disease affecting a wide range of plants and leading to a constant and major challenge to agriculture worldwide. Cotton (Gossypium hirsutum) is the world's most important natural textile fiber and oil crop. VW of cotton is a highly devastating vascular disease, however, few resistant germplasms have been reported in cotton. An increasing number of studies have shown that RNA interference (RNAi) based host-induced gene silencing (HIGS) is an effective strategy for improving plant resistance to pathogens by silencing genes essential for the pathogenicity of these pathogens. Here, we have identified and characterized multifunctional regulators of G protein signaling (RGS) in the Verticillium dahliae virulence strain, Vd8. Of eight VdRGS genes, VdRGS1 showed the most significant increase in expression in V. dahliae after treating with the roots of cotton seedlings. Based on the phenotype detection of VdRGS1 deletion and complementation mutants, we found that VdRGS1 played crucial roles in spore production, hyphal development, microsclerotia formation, and pathogenicity. Tobacco rattle virus (TRV)-mediated HIGS in cotton plants silenced VdRGS1 transcripts in invaded V. dahliae strains, and enhanced broad spectrum resistance to cotton Verticillium wilt. Our data demonstrate that VdRGS1 is a conserved and essential gene for V. dahliae virulence. HIGS of VdRGS1 provide effective control against V. dahliae infection and could obtain the durable disease resistance in cotton, and in other Verticillium wilt-susceptible host crops by developing the stable transformants."

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The Xanthomonas euvesicatoria type III effector XopAU is an active protein kinase that manipulates plant MAP kinase signaling

The Xanthomonas euvesicatoria type III effector XopAU is an active protein kinase that manipulates plant MAP kinase signaling | Fungal-plant interactions | Scoop.it
Author summary Many bacterial pathogens inject effector proteins into their eukaryotic host cells through the type III secretion system to modulate host cellular processes. Elucidating the function of bacterial effectors and identification of their host targets is important for understanding the molecular mechanisms of pathogenicity and host immunity. In this study, we analyzed the mode of action of XopAU, a type III effector from the pepper and tomato pathogen Xanthomonas euvesicatoria. We found that XopAU is a catalytically active protein kinase providing the first report of an effector from a plant bacterial pathogen that displays such an enzymatic activity. We show that expression of XopAU activates immune responses and contributes to the development of disease symptoms. Interestingly, XopAU-mediated phenotypes are altered when the effector is expressed by different species of Xanthomonas, suggesting an interplay between this effector and other species-specific virulence determinants. Furthermore, we provide biochemical and genetic evidence that XopAU interferes with host immune signaling by activating the MAPKK MKK2. Together, our results provide new insights into the interaction between the plant immune system and bacterial type III effector proteins.
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The fungal pathogen Magnaporthe oryzae suppresses innate immunity by modulating a host potassium channel

The fungal pathogen Magnaporthe oryzae suppresses innate immunity by modulating a host potassium channel | Fungal-plant interactions | Scoop.it
Author summary Plant nutritional status can greatly influence plant immunity in response to pathogen invasion. Rice blast, a devastating rice disease caused by the hemibiotrophic fungus Magnaporthe oryzae, causes a significant reduction in yield and affects food security. In this study, we demonstrate that the M. oryzae secreted protein AvrPiz-t interacts with rice OsAKT1, a potassium (K+) channel protein, and suppresses OsAKT1-mediated inward K+ currents, possibly by competing with the OsAKT1 upstream regulator, OsCIPK23. We also show that both OsAKT1 and OsCIPK23 are required for K+ uptake and resistance against M. oryzae infection in rice. This study provides new insights into the molecular basis of pathogen-mediated perturbation of a plant nutrition pathway.
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Genome Biology: RNA virus interference via CRISPR/Cas13a system in plants (2018)

Genome Biology: RNA virus interference via CRISPR/Cas13a system in plants (2018) | Fungal-plant interactions | Scoop.it

Background. CRISPR/Cas systems confer immunity against invading nucleic acids and phages in bacteria and archaea. CRISPR/Cas13a (known previously as C2c2) is a class 2 type VI-A ribonuclease capable of targeting and cleaving single-stranded RNA (ssRNA) molecules of the phage genome. Here, we employ CRISPR/Cas13a to engineer interference with an RNA virus, Turnip Mosaic Virus (TuMV), in plants.

 

Results. CRISPR/Cas13a produces interference against green fluorescent protein (GFP)-expressing TuMV in transient assays and stable overexpression lines of Nicotiana benthamiana. CRISPR RNA (crRNAs) targeting the HC-Pro and GFP sequences exhibit better interference than those targeting other regions such as coat protein (CP) sequence. Cas13a can also process pre-crRNAs into functional crRNAs.

 

Conclusions. Our data indicate that CRISPR/Cas13a can be used for engineering interference against RNA viruses, providing a potential novel mechanism for RNA-guided immunity against RNA viruses and for other RNA manipulations in plants.


Via Kamoun Lab @ TSL
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An unconventional NOI/RIN4 domain of a rice NLR protein binds host EXO70 protein to confer fungal immunity

An unconventional NOI/RIN4 domain of a rice NLR protein binds host EXO70 protein to confer fungal immunity | Fungal-plant interactions | Scoop.it
A subset of plant nucleotide-binding domain and leucine-rich repeat-containing (NLR) proteins carry extraneous integrated domains that have been proposed to mediate pathogen effector recognition. The current view is that these unconventional domains function by directly binding or serving as substrates for pathogen effectors, yet only a few domains have been functionally characterized to date. Here we report that the integrated NOI domain of the rice NLR protein Pii-2, together with its partner Pii-1, mediates immunity to the rice blast fungus Magnaporthe oryzae by indirect recognition of the AVR-Pii effector. We discovered that the Pii-2 NOI domain does not physically interact with the effector itself but instead binds the host protein OsExo70-F3, which is a target of AVR-Pii. We further identified mutations within the NOI core motif (PxFGxW) of Pii-2 that abolish both OsExo70-F3 binding and Pii-mediated resistance to M. oryzae expressing AVR-Pii. This led us to propose a novel conceptual model in which an NLR-integrated domain functions to detect host proteins targeted by pathogen effectors, in a framework that extends classical indirect recognition models.
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A 1-phytase type III effector interferes with plant hormone signaling

A 1-phytase type III effector interferes with plant hormone signaling | Fungal-plant interactions | Scoop.it
Most Gram-negative phytopathogenic bacteria inject type III effector (T3E) proteins into plant cells to manipulate signaling pathways to the pathogen’s benefit. In resistant plants, specialized immune receptors recognize single T3Es or their biochemical activities, thus halting pathogen ingress. However, molecular function and mode of recognition for most T3Es remains elusive. Here, we show that the Xanthomonas T3E XopH possesses phytase activity, i.e., dephosphorylates phytate (myo-inositol-hexakisphosphate, InsP6), the major phosphate storage compound in plants, which is also involved in pathogen defense. A combination of biochemical approaches, including a new NMR-based method to discriminate inositol polyphosphate enantiomers, identifies XopH as a naturally occurring 1-phytase that dephosphorylates InsP6 at C1. Infection of Nicotiana benthamiana and pepper by Xanthomonas results in a XopH-dependent conversion of InsP6 to InsP5. 1-phytase activity is required for XopH-mediated immunity of plants carrying the Bs7 resistance gene, and for induction of jasmonate- and ethylene-responsive genes in N. benthamiana.


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Complex regulation of plant sex by peptides

Complex regulation of plant sex by peptides | Fungal-plant interactions | Scoop.it
Most of our food—whether fruit or grain—is the direct result of flowering plant fertilization. As this also underlies the transmission of genetic information over generations, it is essential to understand the molecular events controlling plant reproduction. During fertilization, pollen (the male gametophyte, or reproductive cell) forms a pollen tube which is guided toward the ovule (the female gametophyte), where, upon bursting, it will deliver its sperm cells (1). All steps—from the perception of compatible pollens by the flower pistil (the female reproductive organ) to pollen tube growth, guidance and, ultimately, rupture—are controlled by a complex molecular dialogue involving numerous plant receptor kinases and endogenous signaling molecules, including secreted peptides (2). On pages 1596 and 1600 of this issue, Ge et al. (3) and Mecchia et al. (4), respectively, characterize signaling events between the male and female gametophytes, which offer exciting insights into the molecular mechanisms controlling plant fertilization and seed setting.

Via Loïc Lepiniec, Saclay Plant Sciences, Francis Martin
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Rescooped by Wheat Pathogenomics from MycorWeb Plant-Microbe Interactions
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Loss of AvrSr50 by somatic exchange in stem rust leads to virulence for Sr50 resistance in wheat

Loss of AvrSr50 by somatic exchange in stem rust leads to virulence for Sr50 resistance in wheat | Fungal-plant interactions | Scoop.it
Race-specific resistance genes protect the global wheat crop from stem rust disease caused by Puccinia graminis f. sp. tritici (Pgt) but are often overcome owing to evolution of new virulent races of the pathogen. To understand virulence evolution in Pgt, we identified the protein ligand (AvrSr50) recognized by the Sr50 resistance protein. A spontaneous mutant of Pgt virulent to Sr50 contained a 2.5 mega–base pair loss-of-heterozygosity event. A haustorial secreted protein from this region triggers Sr50-dependent defense responses in planta and interacts directly with the Sr50 protein. Virulence alleles of AvrSr50 have arisen through DNA insertion and sequence divergence, and our data provide molecular evidence that in addition to sexual recombination, somatic exchange can play a role in the emergence of new virulence traits in Pgt.

Via Francis Martin
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Rescooped by Wheat Pathogenomics from Plants and Microbes
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Science: Eudicot plant-specific sphingolipids determine host selectivity of microbial NLP cytolysins (2017)

Science: Eudicot plant-specific sphingolipids determine host selectivity of microbial NLP cytolysins (2017) | Fungal-plant interactions | Scoop.it

Necrosis and ethylene-inducing peptide 1–like (NLP) proteins constitute a superfamily of proteins produced by plant pathogenic bacteria, fungi, and oomycetes. Many NLPs are cytotoxins that facilitate microbial infection of eudicot, but not of monocot plants. Here, we report glycosylinositol phosphorylceramide (GIPC) sphingolipids as NLP toxin receptors. Plant mutants with altered GIPC composition were more resistant to NLP toxins. Binding studies and x-ray crystallography showed that NLPs form complexes with terminal monomeric hexose moieties of GIPCs that result in conformational changes within the toxin. Insensitivity to NLP cytolysins of monocot plants may be explained by the length of the GIPC head group and the architecture of the NLP sugar-binding site. We unveil early steps in NLP cytolysin action that determine plant clade-specific toxin selectivity.

 

See also commentary by Guido Van den Ackerveken "How plants differ in toxin-sensitivity".

 

Bailey et al. 1995. on Fusarioum Nep1.


Via Kamoun Lab @ TSL
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