Arabidopsis RIN4 Is a Target of the Type III Virulence Effector AvrRpt2 and Modulates RPS2-Mediated Resistance

Type III pili deliver effector proteins (virulence factors) from bacterial pathogens to host cells. Plants express disease resistance (R) proteins that respond specifically to a particular type III effector by activating immune responses. We demonstrated previously that two unrelated type III effectors from Pseudomonas syringae target and modify the Arabidopsis RIN4 protein. Here, we show that AvrRpt2, a third, unrelated type III effector, also targets RIN4 and induces its posttranscriptional disappearance. This effect is independent of the presence of RPS2, the Arabidopsis R protein that senses AvrRpt2. RIN4 overexpression inhibits multiple phenotypes associated with AvrRpt2 function. Conversely, disruption of RIN4 results in RPS2-dependent lethality. RPS2 and RIN4 physically associate in the plant. We suggest that RIN4 is the target of the AvrRpt2 virulence function, and that perturbation of RIN4 activates RPS2. Thus, RIN4 is a point of convergence for the activity of at least three unrelated P. syringae type III effectors.