The RXLR effector PpE18 of Phytophthora parasitica is a virulence factor and suppresses peroxisome membrane‐associated ascorbate peroxidase NbAPX3‐1‐mediated plant immunity.

Summary: Phytophthora parasitica causes diseases on a broad range of host plants. It secretes numerous effectors to suppress plant immunity. However, only a few virulence effectors in P. parasitica have been characterized.Here, we highlight that PpE18, a conserved RXLR effector in P. parasitica, was a virulence factor and suppresses Nicotiana benthamiana immunity. Utilizing luciferase complementation, co‐immunoprecipitation, and GST pull‐down assays, we determined that PpE18 targeted NbAPX3‐1, a peroxisome membrane‐associated ascorbate peroxidase with reactive oxygen species (ROS)‐scavenging activity and positively regulates plant immunity in N. benthamiana. We show that the ROS‐scavenging activity of NbAPX3‐1 was critical for its immune function and was hindered by the binding of PpE18. The interaction between PpE18 and NbAPX3‐1 resulted in an elevation of ROS levels in the peroxisome.Moreover, we discovered that the ankyrin repeat‐containing protein NbANKr2 acted as a positive immune regulator, interacting with both NbAPX3‐1 and PpE18. NbANKr2 was required for NbAPX3‐1‐mediated disease resistance. PpE18 competitively interfered with the interaction between NbAPX3‐1 and NbANKr2, thereby weakening plant resistance.Our results reveal an effective counter‐defense mechanism by which P. parasitica employed effector PpE18 to suppress host cellular defense, by suppressing biochemical activity and disturbing immune function of NbAPX3‐1 during infection. [ABSTRACT FROM AUTHOR]