scholarly journals The RXLR Effector PcAvh1 Is Required for Full Virulence of Phytophthora capsici

2019 ◽  
Vol 32 (8) ◽  
pp. 986-1000 ◽  
Author(s):  
Xiao-Ren Chen ◽  
Ye Zhang ◽  
Hai-Yang Li ◽  
Zi-Hui Zhang ◽  
Gui-Lin Sheng ◽  
...  
Keyword(s):  
Plant Pathogens ◽  
Plant Immunity ◽  
Phytophthora Capsici ◽  
Ectopic Expression ◽  
Plant Cells ◽  
Effector Proteins ◽  
Bell Pepper ◽  
Broad Host Range ◽  
Virus Induced Gene Silencing ◽  
Rxlr Effector

Plant pathogens employ diverse secreted effector proteins to manipulate host physiology and defense in order to foster diseases. The destructive Phytophthora pathogens encode hundreds of cytoplasmic effectors, which are believed to function inside the plant cells. Many of these cytoplasmic effectors contain the conserved N-terminal RXLR motif. Understanding the virulence function of RXLR effectors will provide important knowledge of Phytophthora pathogenesis. Here, we report the characterization of RXLR effector PcAvh1 from the broad–host range pathogen Phytophthora capsici. Only expressed during infection, PcAvh1 is quickly induced at the early infection stages. CRISPR/Cas9-knockout of PcAvh1 in P. capsici severely impairs virulence while overexpression enhances disease development in Nicotiana benthamiana and bell pepper, demonstrating that PcAvh1 is an essential virulence factor. Ectopic expression of PcAvh1 induces cell death in N. benthamiana, tomato, and bell pepper. Using yeast two-hybrid screening, we found that PcAvh1 interacts with the scaffolding subunit of the protein phosphatase 2A (PP2Aa) in plant cells. Virus-induced gene silencing of PP2Aa in N. benthamiana attenuates resistance to P. capsici and results in dwarfism, suggesting that PP2Aa regulates plant immunity and growth. Collectively, these results suggest that PcAvh1 contributes to P. capsici infection, probably through its interaction with host PP2Aa.

scholarly journals A Phytophthora capsici RXLR effector manipulates plant immunity by targeting RAB proteins and disturbing vesicle-mediated protein trafficking pathway

2021 ◽  
Author(s):  
Tianli Li ◽  
Gan Ai ◽  
Xiaowei Fu ◽  
Jin Liu ◽  
Hai Zhu ◽  
...  
Keyword(s):  
Membrane Trafficking ◽  
Plant Immunity ◽  
Phytophthora Capsici ◽  
Functional Characterization ◽  
Ectopic Expression ◽  
Defense Responses ◽  
Infection Process ◽  
Small Gtpase ◽  
Rab Proteins ◽  
Rxlr Effector

The oomycete pathogen Phytophthora capsici encodes hundreds of RXLR effectors to enter plant cells and suppress host defense responses. Only few of them are conserved across different strains and species. Such ‘core effectors’ may target hub immunity pathways that are essential during Phytophthora pathogens interacting with their hosts. However, the underlying mechanisms of core RXLRs-mediated host immunity manipulation are largely unknown. Here, we report the functional characterization of a P. capsici RXLR effector, RXLR242. RXLR242 expression is highly induced during the infection process. Its ectopic expression in Nicotiana benthamiana promotes Phytophthora infection. RXLR242 physically interacts with a group of RAB proteins, which belong to the small GTPase family and function in specifying transport pathways in the intracellular membrane trafficking system. RXLR242 impedes the secretion of PATHOGENESIS-RELATED 1 (PR1) protein to the apoplast by interfering the formation of RABE1-7-labeled vesicles. Further analysis indicated that such phenomenon is resulted from competitive binding of RXLR242 to RABE1-7. RXLR242 also interferes trafficking of the membrane-located receptor FLAGELLIN-SENSING 2 (FLS2) through competitively interacting with RABA4-3. Taken together, our work demonstrates that RXLR242 manipulates plant immunity by targeting RAB proteins and disturbing vesicle-mediated protein transporting pathway in plant hosts.

scholarly journals Bridging the Gap: Type III Secretion Systems in Plant-Beneficial Bacteria

2022 ◽  
Vol 10 (1) ◽  
pp. 187
Author(s):  
Antoine Zboralski ◽  
Adrien Biessy ◽  
Martin Filion
Keyword(s):  
Type Iii Secretion ◽  
Plant Pathogens ◽  
Plant Immunity ◽  
Effector Proteins ◽  
Secretion Systems ◽  
Beneficial Bacteria ◽  
Living Plant ◽  
Pseudomonas Spp ◽  
Type Iii ◽  
Type Iii Secretion Systems

Type III secretion systems (T3SSs) are bacterial membrane-embedded nanomachines translocating effector proteins into the cytoplasm of eukaryotic cells. They have been intensively studied for their important roles in animal and plant bacterial diseases. Over the past two decades, genome sequencing has unveiled their ubiquitous distribution in many taxa of Gram-negative bacteria, including plant-beneficial ones. Here, we discuss the distribution and functions of the T3SS in two agronomically important bacterial groups: the symbiotic nodule-forming nitrogen-fixing rhizobia and the free-living plant-beneficial Pseudomonas spp. In legume-rhizobia symbiosis, T3SSs and their cognate effectors play important roles, including the modulation of the plant immune response and the initiation of the nodulation process in some cases. In plant-beneficial Pseudomonas spp., the roles of T3SSs are not fully understood, but pertain to plant immunity suppression, biocontrol against eukaryotic plant pathogens, mycorrhization facilitation, and possibly resistance against protist predation. The diversity of T3SSs in plant-beneficial bacteria points to their important roles in multifarious interkingdom interactions in the rhizosphere. We argue that the gap in research on T3SSs in plant-beneficial bacteria must be bridged to better understand bacteria/eukaryotes rhizosphere interactions and to support the development of efficient plant-growth promoting microbial inoculants.

scholarly journals Secretome Analysis and In Planta Expression of Salivary Proteins Identify Candidate Effectors from the Brown Planthopper Nilaparvata lugens

2019 ◽  
Vol 32 (2) ◽  
pp. 227-239 ◽  
Author(s):  
Weiwei Rao ◽  
Xiaohong Zheng ◽  
Bingfang Liu ◽  
Qin Guo ◽  
Jianping Guo ◽  
...  
Keyword(s):  
Cell Death ◽  
Expression Analysis ◽  
Plant Pathogens ◽  
Critical Role ◽  
Brown Planthopper ◽  
Ectopic Expression ◽  
Nilaparvata Lugens ◽  
Effector Proteins ◽  
Salivary Proteins ◽  
Secretome Analysis

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a phloem sap-feeding insect. During feeding on rice plants, BPH secretes salivary proteins with potential effector functions, which may play a critical role in the plant–insect interactions. However, a limited number of BPH effector proteins have been identified to date. Here, we sequenced the salivary gland transcriptomes of five BPH populations and subsequently established a N. lugens secretome consisting of 1,140 protein-encoding genes. Secretome analysis revealed the presence of both conserved and rapidly evolving salivary proteins. A screen for potential effectors that elicit responses in the plant was performed via the transient expression analysis of 64 BPH salivary proteins in Nicotiana benthamiana leaves and rice protoplasts. The salivary proteins Nl12, Nl16, Nl28, and Nl43 induced cell death, whereas Nl40 induced chlorosis and Nl32 induced a dwarf phenotype in N. benthamiana, indicating effector properties of these proteins. Ectopic expression of the six salivary proteins in N. benthamiana upregulated expression of defense-related genes and callose deposition. Tissue expression analysis showed a higher expression level of the six candidate effectors in salivary glands than in other tissues. Subcellular localization and analysis of the domain required for cell death showed a diverse structure of the six effectors. Nl28, Nl40, and Nl43 are N. lugens specific; in contrast, Nl12, Nl16, and Nl32 are conserved among insects. The Nl40 family has numerous isoforms produced by alternative splicing, exemplifying rapid evolution and expansion of effector proteins in the BPH. Our results suggest a potential large effector repertoire in BPH and a higher level of effector conservation exist in BPH compared with that in plant pathogens.

scholarly journals Downy Mildew effector HaRxL21 interacts with the transcriptional repressor TOPLESS to promote pathogen susceptibility

2020 ◽  
Author(s):  
Sarah Harvey ◽  
Priyanka Kumari ◽  
Dmitry Lapin ◽  
Thomas Griebel ◽  
Richard Hickman ◽  
...  
Keyword(s):  
Downy Mildew ◽  
Transcriptional Repression ◽  
Plant Immunity ◽  
Effector Proteins ◽  
Host Susceptibility ◽  
Close Relative ◽  
C Terminus ◽  
Rxlr Effector ◽  
Oomycete Pathogen ◽  
Hyaloperonospora Arabidopsidis

AbstractHyaloperonospora arabidopsidis (Hpa) is an oomycete pathogen causing Arabidopsis downy mildew. Effector proteins secreted from the pathogen into the plant play key roles in promoting infection by suppressing plant immunity and manipulating the host to the pathogen’s advantage. One class of oomycete effectors share a conserved ‘RxLR’ motif critical for their translocation into the host cell. Here we characterize the interaction between an RxLR effector, HaRxL21 (RxL21), and the Arabidopsis transcriptional co-repressor Topless (TPL). We establish that RxL21 and TPL interact via an EAR motif at the C-terminus of the effector, mimicking the host plant mechanism for recruiting TPL to sites of transcriptional repression. We show that this motif, and hence interaction with TPL, is necessary for the virulence function of the effector. Furthermore, we provide evidence that RxL21 uses the interaction with TPL, and its close relative TPL-related 1, to repress plant immunity and enhance host susceptibility to both biotrophic and necrotrophic pathogens.

scholarly journals A Phytophthora sojae CRN effector mediates phosphorylation and degradation of plant aquaporin proteins to suppress host immune signaling

2021 ◽  
Vol 17 (3) ◽  
pp. e1009388
Author(s):  
Gan Ai ◽  
Qingyue Xia ◽  
Tianqiao Song ◽  
Tianli Li ◽  
Hai Zhu ◽  
...  
Keyword(s):  
Higher Plants ◽  
Plant Immunity ◽  
Phytophthora Capsici ◽  
Kinase Domain ◽  
Phytophthora Sojae ◽  
Effector Proteins ◽  
Ros Accumulation ◽  
Oomycete Pathogen ◽  
Cellular Defenses

Phytophthora genomes encode a myriad of Crinkler (CRN) effectors, some of which contain putative kinase domains. Little is known about the host targets of these kinase-domain-containing CRNs and their infection-promoting mechanisms. Here, we report the host target and functional mechanism of a conserved kinase CRN effector named CRN78 in a notorious oomycete pathogen, Phytophthora sojae. CRN78 promotes Phytophthora capsici infection in Nicotiana benthamiana and enhances P. sojae virulence on the host plant Glycine max by inhibiting plant H2O2 accumulation and immunity-related gene expression. Further investigation reveals that CRN78 interacts with PIP2-family aquaporin proteins including NbPIP2;2 from N. benthamiana and GmPIP2-13 from soybean on the plant plasma membrane, and membrane localization is necessary for virulence of CRN78. Next, CRN78 promotes phosphorylation of NbPIP2;2 or GmPIP2-13 using its kinase domain in vivo, leading to their subsequent protein degradation in a 26S-dependent pathway. Our data also demonstrates that NbPIP2;2 acts as a H2O2 transporter to positively regulate plant immunity and reactive oxygen species (ROS) accumulation. Phylogenetic analysis suggests that the phosphorylation sites of PIP2 proteins and the kinase domains of CRN78 homologs are highly conserved among higher plants and oomycete pathogens, respectively. Therefore, this study elucidates a conserved and novel pathway used by effector proteins to inhibit host cellular defenses by targeting and hijacking phosphorylation of plant aquaporin proteins.

scholarly journals A small secreted protein from Zymoseptoria tritici interacts with a wheat E3 ubiquitin ligase to promote disease

2020 ◽  
Author(s):  
Sujit Jung Karki ◽  
Aisling Reilly ◽  
Binbin Zhou ◽  
Maurizio Mascarello ◽  
James Burke ◽  
...  
Keyword(s):  
Ubiquitin Ligase ◽  
Plant Pathogens ◽  
Plant Immunity ◽  
E3 Ubiquitin Ligase ◽  
Bimolecular Fluorescence Complementation ◽  
Septoria Tritici Blotch ◽  
Septoria Tritici ◽  
Virus Induced Gene Silencing ◽  
In Planta ◽  
Zymoseptoria Tritici

Abstract Septoria tritici blotch (STB), caused by the ascomycete fungus Zymoseptoria tritici, is a major threat to wheat production worldwide. The Z. tritici genome encodes many small secreted proteins (ZtSSPs) that are likely to play a key role in the successful colonization of host tissues. However, few of these ZtSSPs have been functionally characterized for their role during infection. In this study, we identified and characterized a small, conserved cysteine-rich secreted effector from Z. tritici which has homologues in other plant pathogens in the Dothideomycetes. ZtSSP2 was expressed throughout Z. tritici infection in wheat, with the highest levels observed early during infection. A yeast two-hybrid assay revealed an interaction between ZtSSP2 and wheat E3 ubiquitin ligase (TaE3UBQ) in yeast, and this was further confirmed in planta using bimolecular fluorescence complementation and co-immunoprecipitation. Down-regulation of this wheat E3 ligase using virus-induced gene silencing increased the susceptibility of wheat to STB. Together, these results suggest that TaE3UBQ is likely to play a role in plant immunity to defend against Z. tritici.

scholarly journals Ralstonia solanacearum Type III Effector RipAY Is a Glutathione-Degrading Enzyme That Is Activated by Plant Cytosolic Thioredoxins and Suppresses Plant Immunity

mBio ◽  
2016 ◽  
Vol 7 (2) ◽  
Author(s):  
Takafumi Mukaihara ◽  
Tadashi Hatanaka ◽  
Masahito Nakano ◽  
Kenji Oda
Keyword(s):  
Immune System ◽  
Ralstonia Solanacearum ◽  
Plant Immunity ◽  
Plant Cells ◽  
Effector Proteins ◽  
Yeast Cells ◽  
Yeast Growth ◽  
Type Iii Effector ◽  
Plant Immune System ◽  
Degradation Activity

ABSTRACT The plant pathogen Ralstonia solanacearum uses a large repertoire of type III effector proteins to succeed in infection. To clarify the function of effector proteins in host eukaryote cells, we expressed effectors in yeast cells and identified seven effector proteins that interfere with yeast growth. One of the effector proteins, RipAY, was found to share homology with the ChaC family proteins that function as γ-glutamyl cyclotransferases, which degrade glutathione (GSH), a tripeptide that plays important roles in the plant immune system. RipAY significantly inhibited yeast growth and simultaneously induced rapid GSH depletion when expressed in yeast cells. The in vitro GSH degradation activity of RipAY is specifically activated by eukaryotic factors in the yeast and plant extracts. Biochemical purification of the yeast protein identified that RipAY is activated by thioredoxin TRX2. On the other hand, RipAY was not activated by bacterial thioredoxins. Interestingly, RipAY was activated by plant h -type thioredoxins that exist in large amounts in the plant cytosol, but not by chloroplastic m -, f -, x -, y - and z -type thioredoxins, in a thiol-independent manner. The transient expression of RipAY decreased the GSH level in plant cells and affected the flg22-triggered production of reactive oxygen species (ROS) and expression of pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) marker genes in Nicotiana benthamiana leaves. These results indicate that RipAY is activated by host cytosolic thioredoxins and degrades GSH specifically in plant cells to suppress plant immunity. IMPORTANCE Ralstonia solanacearum is the causal agent of bacterial wilt disease of plants. This pathogen injects virulence effector proteins into host cells to suppress disease resistance responses of plants. In this article, we report a biochemical activity of R. solanacearum effector protein RipAY. RipAY can degrade GSH, a tripeptide that plays important roles in the plant immune system, with its γ-glutamyl cyclotransferase activity. The high GSH degradation activity of RipAY is considered to be a good weapon for this bacterium to suppress plant immunity. However, GSH also plays important roles in bacterial tolerance to various stresses and growth. Interestingly, RipAY has an excellent safety mechanism to prevent unwanted firing of its enzyme activity in bacterial cells because RipAY is specifically activated by host eukaryotic thioredoxins. This study also reveals a novel host plant protein acting as a molecular switch for effector activation.

Host apoplastic cysteine protease activity is suppressed during the mutualistic association of Lolium perenne and Epichloë festucae

2021 ◽  
Vol 72 (9) ◽  
pp. 3410-3426
Author(s):  
Andrea Passarge ◽  
Fatih Demir ◽  
Kimberly Green ◽  
Jasper R L Depotter ◽  
Barry Scott ◽  
...  
Keyword(s):  
Lolium Perenne ◽  
Plant Pathogens ◽  
Plant Immunity ◽  
Evolutionary Relationship ◽  
Cysteine Proteases ◽  
Effector Proteins ◽  
Protein Profiling ◽  
Epichloë Festucae ◽  
A Genome ◽  
Mutualistic Association

Abstract Plants secrete various defence-related proteins into the apoplast, including proteases. Papain-like cysteine proteases (PLCPs) are central components of the plant immune system. To overcome plant immunity and successfully colonize their hosts, several plant pathogens secrete effector proteins inhibiting plant PLCPs. We hypothesized that not only pathogens, but also mutualistic microorganisms interfere with PLCP-meditated plant defences to maintain endophytic colonization with their hosts. Epichloë festucae forms mutualistic associations with cool season grasses and produces a range of secondary metabolites that protect the host against herbivores. In this study, we performed a genome-wide identification of Lolium perenne PLCPs, analysed their evolutionary relationship, and classified them into nine PLCP subfamilies. Using activity-based protein profiling, we identified four active PLCPs in the apoplast of L. perenne leaves that are inhibited during endophyte interactions. We characterized the L. perenne cystatin LpCys1 for its inhibitory capacity against ryegrass PLCPs. LpCys1 abundance is not altered during the mutualistic interaction and it mainly inhibits LpCP2. However, since the activity of other L. perenne PLCPs is not sensitive to LpCys1, we propose that additional inhibitors, likely of fungal origin, are involved in the suppression of apoplastic PLCPs during E. festucae infection.

scholarly journals Plasmodiophora brassicae CBM18 proteins bind chitin and suppress chitin-triggered immunity

2021 ◽  
Author(s):  
Kevin Muirhead ◽  
Edel Pérez-López
Keyword(s):  
Plant Pathogens ◽  
Plasmodiophora Brassicae ◽  
Plant Immunity ◽  
Effector Proteins ◽  
Carbohydrate Binding ◽  
Chitin Deacetylase ◽  
Chitin Binding Domain ◽  
A Genome ◽  
Co Precipitation ◽  
Main Component

Plants have a sophisticated and multi-layered immune system. However, plant pathogens, helped by effector proteins, have found several strategies to evade plant immunity. For instance, the clubroot pathogen, Plasmodiophora brassicae, is able to turn the roots of the susceptible hosts into nutrient-sink galls surpassing patterns-triggered immunity (PTI) and effector-triggered immunity (ETI). Chitin, the main component of P. brassicae spore cell walls and a well-known pathogens-associated molecular pattern (PAMP), can elicit PTI but is also the target of plant chitinases and chitin deacetylases. The fact that P. brassicae does not trigger PTI during infection of the susceptible hosts motivated a genome-wide search of genes coding for secreted proteins with domains previously associated to chitin binding. We found that P. brassicae genome encodes a repertoire of candidate-secreted effectors containing the chitin-binding domain carbohydrate-binding module family 18 (CBM18), chitinase, and chitin deacetylase domains. The role of these proteins in the pathogenicity of the clubroot pathogen is unknown. Here, we characterized two CBM18 proteins, PbChiB2 and PbChiB4, which are transcriptionally activated during infection. Through co-precipitation, we found that recombinant PbChiB2 and PbChiB4 bind to spores and to chitin oligomers. We also showed that both proteins suppress chitin-triggered activation of the map kinase proteins MPK3 and MPK6 in the host Brassica napus. These findings suggest that P. brassicae CBM18 proteins act as effectors for protecting the clubroot pathogen and for suppressing chitin-triggered immunity during infection.

A Phytophthora capsici RXLR effector targets and inhibits the central immune kinases to suppress plant immunity

2021 ◽  
Author(s):  
Xiangxiu Liang ◽  
Yazhou Bao ◽  
Meixiang Zhang ◽  
Dandan Du ◽  
Shaofei Rao ◽  
...  
Keyword(s):  
Plant Immunity ◽  
Phytophthora Capsici ◽  
Rxlr Effector
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