Abstract
Phytophthora infestans is a notorious oomycete pathogen that causes potato late blight. It secretes numerous effector proteins to manipulate host immunity. Understanding mechanisms underlying their host cell manipulation is crucial for developing disease resistance strategies. Here, we report that the conserved RXLR effector Pi05910 of P. infestans is a genotype-specific avirulence elicitor on potato variety Longshu 12 and contributes virulence by suppressing and destabilizing host glycolate oxidase StGOX4. By performing co-immunoprecipitation, yeast-two-hybrid assays, luciferase complementation imaging, bimolecular fluorescence complementation and isothermal titration calorimetry assays, we identified and confirmed potato StGOX4 as a target of Pi05910. Further analysis revealed that StGOX4 and its homologue NbGOX4 are positive immune regulators against P. infestans, as indicated by infection assays on potato and Nicotiana benthamiana overexpressing StGOX4 and TRV-NbGOX4 plants. StGOX4-mediated disease resistance involves enhanced reactive oxygen species accumulation and activated the salicylic acid signalling pathway. Pi05910 binding inhibited enzymatic activity and destabilized StGOX4. Furthermore, mutagenesis analyses indicated that the 25th residue (tyrosine, Y25) of StGOX4 mediates Pi05910 binding and is required for its immune function. Our results revealed that the core RXLR effector of P. infestans Pi05910 suppresses plant immunity by targeting StGOX4, which results in decreased enzymatic activity and protein accumulation, leading to enhanced plant susceptibility.