RNA干扰是由与靶基因序列同源的双链RNA介导的特异性基因沉默现象，参与调控基因表达、抵抗病毒入侵、抑制转座子活动等多种重要生物学功能。大豆疫霉菌是一种能够引起大豆根茎腐烂的卵菌病原菌，是全球第二大具有破坏性作用的大豆疾病致病菌。研究表明，大豆疫霉菌能够利用自身的效应蛋白PSR2抑制宿主RNAi途径，抵抗宿主免疫，促进病原菌的感染。PSR2属于RxRL家族蛋白，具有典型的RxRL基序。RxRL家族蛋白在植物病原菌中大量存在，然而迄今为止，该家族蛋白的结构及其发挥功能的分子机制尚不清楚。本项目将主要围绕大豆疫霉菌效应蛋白PSR2及其宿主互作蛋白DRB4，主要运用蛋白质晶体学，结合冷冻电镜和体外生化实验等多种方法，解析PSR2自身及其与宿主中重要的RNAi途径蛋白DRB4复合物的三维结构，阐明其跨界抑制宿主RNAi途径的分子机制，从而为大豆农业生产和国家食品安全提供可能的全新方案。

RNA interference (RNAi) is a specific gene silencing mechanism by double-stranded RNAs (dsRNAs) that are homologous to target gene sequences. It is involved in many important biological processes, including resistance to viruses, transposon activity inhibition, gene expression regulation, et al. Phytophthora sojae is an oomycete pathogen which can cause soybean rotting, which is the second largest soybean diseases that has devastating effects. Previous study indicated Phytophthora sojae uses its own effector protein PSR2 to inhibit the host RNAi pathway, counteract the immunity of the host, and promote pathogen infection. PSR2 belongs to RxRL family proteins, and contains a conservative RxRL motif. RxRL family proteins are abundant in plant pathogens, but until now, their structures and molecular mechanism of their functions are largely unknown. This project aims to study the Phytophthora sojae effector protein PSR2 and its host interacting protein DRB4, mainly using protein crystallography, in combination with cryo-EM and in vitro biochemical experiments, solve the three-dimensional structures of PSR2 alone and its complex with DRB4 that plays important role in host RNAi pathway, and uncover the molecular mechanism for its trans-kingdom suppression of host RNAi pathway. This work may provide possible brand new solutions for the agriculture production of Phytophthora sojae and national food security.