Host-interactor screens of RXLR effectors reveal plant processes manipulated by Phytophthora

Oomycete plant pathogens deliver RXLR effectors inside plant cells to alter host processes to their advantage. Effectors interact with plant proteins including their cognate targets and helpers to achieve their functions. This study aims to identify the plant proteins interacting with RXLR effectors and ultimately the function of the effectors in planta. We transiently expressed 75 FLAG-tagged RXLR effectors in Nicotiana benthamianausing the high-expression vector pTRBO. Effector fusions and associated host proteins were co-immunoprecipitated (co-IP) and identified by LC-MS/MS spectrum matching against N. benthamianaproteome database. Out of 75 effectors, 53 were expressed to sufficient levels for co-IP and identification by mass spectrometry. GO annotation of associated plant proteins revealed 48 plant processes that might be targeted by the effectors. We classified the candidate interacters with a scoring system. So far, we confirmed more than 20 effector-plant protein associations. Notably, we found that the PEXRD12/31 effectors associated and co-localized with components of vesicle trafficking machinery including VAMPs, VAC14, coatomers, vesicle fusing ATPase, syntaxin, exocyst, and Ras-related proteins. PEXRD31 increased the number of FYVE-labelled endosomal membrane compartments in plant cells, suggesting that the effector modulates a process related to endosomal trafficking. We will discuss these findings and their implications for plant-oomycete interactions.