Abstract
In plants, the apoplast is a critical battlefield for plant-microbe interactions. Plants secrete defense-related proteins into the apoplast to ward off the invasion of pathogens. How microbial pathogens overcome plant apoplastic immunity remains largely unknown. In this study, we reported that an atypical RxLR effector PsAvh181 secreted by Phytophthora sojae, inhibits the secretion of plant defense-related apoplastic proteins. PsAvh181 localizes to plant plasma membrane and essential for P. sojae infection. By co-immunoprecipitation assay followed by liquid chromatography-tandem mass spectrometry analyses, we identified the soybean GmSNAP-1 as a candidate host target of PsAvh181. GmSNAP-1 encodes a soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein, which associates with GmNSF of the SNARE complex functioning in vesicle trafficking. PsAvh181 binds to GmSNAP-1 in vivo and in vitro. PsAvh181 interferes with the interaction between GmSNAP-1 and GmNSF, and blocks the secretion of apoplastic defense-related proteins, such as pathogenesis-related protein PR-1 and apoplastic proteases. Taken together, these data show that an atypical P. sojae RxLR effector suppresses host apoplastic immunity by manipulating the host SNARE complex to interfere with host vesicle trafficking pathway.
Highlights
The plant apoplast space is a major site of host-pathogen interactions [1]
We found that PsAvh181 localizes to the plant plasma membrane to inhibit the secretion of apoplastic defense-related proteins such as GmGIP1, P69B and PR1
Since GmGIP1 acts as an important resistance component in soybean by inhibiting P. sojae glycoside hydrolase PsXEG1 [7], we determined whether P. sojae counters this defense mechanism by interfering with the secretion of GmGIP1 into the apoplast
Summary
The plant apoplast space is a major site of host-pathogen interactions [1]. Upon infection by microbial pathogens, plants secrete multiple defense-related proteins into the apoplast, such as proteases and protease inhibitors [1]. P69B, an apoplastic serine protease that belongs to the extracellular subtilisin-like protease family from tomato, contributes to resistance to pathogens [3]. C14 is a papain-like Cys protease secreted by tomato that contributes to resistance against the oomycete pathogen P. infestans [5]. P. sojae secretes the glycoside hydrolase 12 protein PsXEG1 into plant apoplasts, while PsXEG1 facilitates infection as a major virulence factor [6]. GmGIP1 can inhibit the hydrolase enzyme activity and virulence of PsXEG1 to positively regulate plant immunity [7]. GmAP1, the soybean ortholog of CDR1, contributes to defense [8,9]
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