Reactive oxygen species (ROS) play a vital role in plant immune response, but the genes involved in the regulation of ROS are scantily reported. Phytophthora pathogens produce a large number of effectors to promote infection, but the modes of action adopted are largely unknown. Here, we report that RxLR207 could activate ROS-mediated cell death in Nicotiana benthamiana and was essential for virulence of P. capsici. We found that this effector targeted BPA1 (binding partner of ACD11) and four members of BPLs (BPA1-Like proteins) in Arabidopsis, and the bpa1 and bpl mutants had enhanced ROS accumulation and cell death under biotic or abiotic stresses. Furthermore, we showed that BPA1 and several BPLs functioned redundantly in plant immunity to P. capsici. We discovered that BPA1 and all six BPLs interacted with ACD11, and stabilization of ACD11 was impaired in the bpa1, bpl2, bpl3, and bpl4 mutants. RxLR207 could promote the degradation of BPA1, BPL1, BPL2, and BPL4 to disrupt ACD11 stabilization in a 26S proteasome-dependent manner. Taken together, these findings indicate the important roles of Arabidopsis BPA1 and its homologs in ROS homeostasis and defense response, highlighting the usefulness of a pathogen effector-directed approach as a promising strategy for the discovery of novel plant immune regulators.

活性氧（ROS）在植物免疫反应中起着至关重要的作用，但是参与ROS调控的基因却很少。疫霉菌的病原体产生大量的效应物来促进感染，但是所采用的作用方式在很大程度上是未知的。在这里，我们报道RxLR207可以激活本氏烟草中ROS介导的细胞死亡，并且对于P的毒力至关重要。capsici。我们发现，这种效应有针对性的BPA1（结合ACD11的合作伙伴）和BPLs（BPA1样蛋白）中的四名成员拟南芥中，并BPA1和BPL在生物或非生物胁迫下，这些突变体具有增强的ROS积累和细胞死亡。此外，我们表明BPA1和几种BPL在植物对P的免疫中起冗余作用。capsici。我们发现BPA1和所有六个BPL与ACD11相互作用，并且在bpa1，bpl2，bpl3和bpl4突变体中ACD11的稳定性受到损害。RxLR207可以促进BPA1，BPL1，BPL2和BPL4的降解，以26S蛋白酶体依赖性方式破坏ACD11的稳定性。综上所述，这些发现表明拟南芥的重要作用。 BPA1及其在ROS稳态和防御反应中的同源物，突显了病原体效应物指导方法作为发现新型植物免疫调节剂的有希望策略的有用性。