FIRE Mimics a 14-3-3-Binding Motif to Promote Phytophthora palmivora Infection

The oomycete Phytophthora palmivora infects a wide range of tropical crops worldwide. Like other filamentous plant pathogens, it secretes effectors to colonize plant tissues. Here, we characterize FIRE, an RXLR effector that contains a canonical mode I 14-3-3 phospho-sensor-binding motif that is conserved in effectors of several Phytophthora species. FIRE is phosphorylated in planta and interacts with multiple 14-3-3 proteins. Binding is sensitive to the R18 14-3-3 inhibitor. FIRE promotes plant susceptibility and co-localizes with its target around haustoria. Thiswork uncovers a new type of oomycete effector target mechanism. It demonstrates that substrate mimicry for 14-33 proteins is a cross-kingdom effector strategy used by both prokaryotic and eukaryotic plant pathogens to suppress host immunity.