Plants secrete defense molecules into the extracellular space (the apoplast) to combat attacking microbes. However, the mechanisms by which successful pathogens subvert plant apoplastic immunity remain poorly understood. In this study, we show that PsAvh240, a membrane-localized effector of the soybean pathogen Phytophthora sojae, promotes P. sojae infection in soybean hairy roots. We found that PsAvh240 interacts with the soybean-resistant aspartic protease GmAP1 in planta and suppresses the secretion of GmAP1 into the apoplast. By solving its crystal structure we revealed that PsAvh240 contain six α helices and two WY motifs. The first two α helices of PsAvh240 are responsible for its plasma membrane-localization and are required for PsAvh240’s interaction with GmAP1. The second WY motifs of two PsAvh240 molecules form a handshake arrangement resulting in a handshake-like dimer. This dimerization is required for the effector's repression of GmAP1 secretion. Taken together, these data reveal that PsAvh240 localizes at the plasma membrane to interfere with GmAP1 secretion, which represents an effective mechanism by which effector proteins suppress plant apoplastic immunity.

植物将防御分子分泌到细胞外空间（质外体）以对抗微生物的攻击。然而，病原体成功破坏植物质外体免疫的机制仍然知之甚少。在这项研究中，我们发现 PsAvh240（大豆病原体Phytophthora sojae的膜定位效应子）可促进P .大豆毛状根中的大豆感染。我们发现 PsAvh240 与植物中的大豆抗性天冬氨酸蛋白酶 GmAP1 相互作用，并抑制 GmAP1 分泌到质外体中。通过解析其晶体结构，我们发现 PsAvh240 包含六个 α 螺旋和两个 WY 基序。 PsAvh240 的前两个 α 螺旋负责其质膜定位，并且是 PsAvh240 与 GmAP1 相互作用所必需的。两个 PsAvh240 分子的第二个 WY 基序形成握手排列，从而形成握手样二聚体。这种二聚化是效应子抑制 GmAP1 分泌所必需的。综上所述，这些数据表明 PsAvh240 定位于质膜以干扰 GmAP1 分泌，这代表了效应蛋白抑制植物质外体免疫的有效机制。