Oomycete pathogens such as Phytophthora secrete a repertoire of effectors into host cells to manipulate host immunity and benefit infection. In this study, we found that an RxLR effector, Avr1d, promoted Phytophthora sojae infection in soybean hairy roots. Using a yeast two-hybrid screen, we identified the soybean E3 ubiquitin ligase GmPUB13 as a host target for Avr1d. By coimmunoprecipitation (Co-IP), gel infiltration, and isothermal titration calorimetry (ITC) assays, we confirmed that Avr1d interacts with GmPUB13 both in vivo and in vitro. Furthermore, we found that Avr1d inhibits the E3 ligase activity of GmPUB13. The crystal structure Avr1d in complex with GmPUB13 was solved and revealed that Avr1d occupies the binding site for E2 ubiquitin conjugating enzyme on GmPUB13. In line with this, Avr1d competed with E2 ubiquitin conjugating enzymes for GmPUB13 binding in vitro, thereby decreasing the E3 ligase activity of GmPUB13. Meanwhile, we found that inactivation of the ubiquitin ligase activity of GmPUB13 stabilized GmPUB13 by blocking GmPUB13 degradation. Silencing of GmPUB13 in soybean hairy roots decreased P. sojae infection, suggesting that GmPUB13 acts as a susceptibility factor. Altogether, this study highlights a virulence mechanism of Phytophthora effectors, by which Avr1d competes with E2 for GmPUB13 binding to repress the GmPUB13 E3 ligase activity and thereby stabilizing the susceptibility factor GmPUB13 to facilitate Phytophthora infection. This study unravels the structural basis for modulation of host targets by Phytophthora effectors and will be instrumental for boosting plant resistance breeding.

卵菌病原体（例如疫霉属）将一系列效应子分泌到宿主细胞中，以操纵宿主免疫并有利于感染。在这项研究中，我们发现 RxLR 效应子 Avr1d 促进大豆毛状根中的大豆疫霉感染。使用酵母双杂交筛选，我们确定大豆 E3 泛素连接酶 GmPUB13 作为 Avr1d 的宿主靶标。通过免疫共沉淀 (Co-IP)、凝胶渗透和等温滴定量热法 (ITC) 测定，我们证实 Avr1d 在体内和体外均与 GmPUB13 相互作用。此外，我们发现 Avr1d 抑制 GmPUB13 的 E3 连接酶活性。解析了 Avr1d 与 GmPUB13 复合物的晶体结构，并揭示了 Avr1d 占据了 GmPUB13 上 E2 泛素缀合酶的结合位点。与此相符，Avr1d 在体外与 E2 泛素结合酶竞争 GmPUB13 结合，从而降低 GmPUB13 的 E3 连接酶活性。同时，我们发现GmPUB13泛素连接酶活性的失活通过阻止GmPUB13降解来稳定GmPUB13。大豆毛状根中 GmPUB13 的沉默减少了酱油疫霉的感染，表明 GmPUB13 是一个易感因子。总而言之，这项研究强调了疫霉效应子的毒力机制，通过该机制，Avr1d 与 E2 竞争 GmPUB13 结合，抑制 GmPUB13 E3 连接酶活性，从而稳定易感因子 GmPUB13，促进疫霉感染。这项研究揭示了疫霉效应子调节宿主靶标的结构基础，并将有助于促进植物抗性育种。