Effectors of Phytophthora pathogens are powerful weapons for manipulating host immunity.

This article provides an overview of the interactions between Phytophthora effectors and plant immune system components, which form a cross-linked complex network that regulates plant pathogen resistance. Pathogens secrete numerous effector proteins into plants to promote infections. Several Phytophthora species (e.g., P. infestans, P. ramorum, P. sojae, P. capsici, P. cinnamomi, and P. parasitica) are notorious pathogens that are extremely damaging to susceptible plants. Analyses of genomic data revealed that Phytophthora species produce a large group of effector proteins, which are critical for pathogenesis. And, the targets and functions of many identified Phytophthora effectors have been investigated. Phytophthora effectors can affect various aspects of plant immune systems, including plant cell proteases, phytohormones, RNAs, the MAPK pathway, catalase, the ubiquitin proteasome pathway, the endoplasmic reticulum, NB-LRR proteins, and the cell membrane. Clarifying the effector-plant interactions is important for unravelling the functions of Phytophthora effectors during pathogenesis. In this article, we review the effectors identified in recent decades and provide an overview of the effector-directed regulatory network in plants following infections by Phytophthora species.