RIN4 is a small A. thaliana protein localized to the plasma membrane that acts as a negative regulator of plant immunity responses. It interacts with the resistance proteins RPM1 and RPS2 and is targeted by several Pseudomonas syringae effectors like AvrB, AvrRpm1, and AvrRpt2. Current models suggest RIN4 may serve as a decoy to mimic the unknown real targets of these effectors and compete for binding, activating RPM1/RPS2-mediated immunity when effectors modify RIN4. RIN4 also regulates stomatal closure during infection and the evolution of this RIN4-mediated effector-triggered susceptibility system.