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

Abstract

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.

An RXLR effector PlAvh142 from Peronophythora litchii triggers plant cell death and contributes to virulence

“…Examples include PsXEG1 (Ma et al , , ; Wang et al , ), Avh238 (Yang et al , ), and PpE4 (Huang et al , ). Another similar example was reported in the cell death‐inducing RXLR effector, PcAvh1, which is a virulence factor of P. capsici as its deletion mutants displayed reduced pathogenicity in contrast to the more aggressive overexpression mutants (Chen et al , ). Such a seemingly contradictory phenomenon was also observed for PlAvh142 in this study, and we raise the following hypotheses in an attempt to explain this.…”

“…RXLR effectors have become a focus for studying plant–pathogen interaction in the past decade, with numerous effector genes identified and characterized in Phytophthora and downy mildew species (Tyler et al , ; Haas et al , ; Baxter et al , ; Yin et al , ). Many studies have reported that RXLR effectors are involved in the suppression of PTI and/or ETI (Wang et al , ; Kong et al , ; Fan et al , ) Additionally, some of them can trigger immune response‐related cell death, for example Phytophthora sojae Avh238 (Yang et al , ), Phytophthora capsici Avh1 (Chen et al , ), and Plasmopara viticola RXLR16 (Xiang et al , ).…”

Organize, Don’t Agonize: Strategic Success of Phytophthora Species

“…One mechanism that Phytophthora species employ to suppress the host response is targeting crucial defense proteins [110]. Studies show that most RXLRs of Phytophthora target various events of PTI to successfully complete the biotrophic phase.…”

Applications of CRISPR technology in studying plant-pathogen interactions: overview and perspective

“…Furthermore, CRISPR/SpCas9 was also used to knockout another RXLR effector gene PcAvh1 in P. capsici. In this study, inoculation of PcAvh1 mutants on N. benthamiana showed that PcAvh1 was required for the full virulence of P. capsici (Chen et al 2019). CRISPR/SpCas9 system has also been used in P. palmivora to generate homozygous PpalEPIC8 mutants via Agrobacterium-mediated transformation.…”