A duplicated pair of Arabidopsis RING-finger E3 ligases contribute to the RPM1- and RPS2-mediated hypersensitive response.

The Arabidopsis RPM1 protein confers resistance to disease caused by Pseudomonas syringae strains delivering either the AvrRpm1 or AvrB type III effector proteins into host cells. We characterized two closely related RPM1-interacting proteins, RIN2 and RIN3. RIN2 and RIN3 encode RING-finger type ubiquitin ligases with six apparent transmembrane domains and an ubiquitin-binding CUE domain. RIN2 and RIN3 are orthologs of the mammalian autocrine motility factor receptor, a cytokine receptor localized in both plasma membrane caveolae and the endoplasmic reticulum. RIN2 is predominantly localized to the plasma membrane, as are RPM1 and RPS2. The C-terminal regions of RIN2 and RIN3, including the CUE domain, interact strongly with an RPM1 N-terminal fragment and weakly with a similar domain from the Arabidopsis RPS2 protein. RIN2 and RIN3 can dimerize through their C-terminal regions. The RING-finger domains of RIN2 and RIN3 encode ubiquitin ligases. Inoculation with P. syringae DC3000(avrRpm1) or P. syringae DC3000(avrRpt2) induces differential decreases of RIN2 mobility in SDS-PAGE and disappearance of the majority of RIN2. A rin2 rin3 double mutant expresses diminished RPM1- and RPS2-dependent hypersensitive response (HR), but no alteration of pathogen growth. Thus, the RIN2/RIN3 RING E3 ligases apparently act on a substrate that regulates RPM1- and RPS2-dependent HR.