Activation of a Phytopathogenic Bacterial Effector Protein by a Eukaryotic Cyclophilin

Abstract

Innate immunity in higher plants invokes a sophisticated surveillance system capable of recognizing bacterial effector proteins. In Arabidopsis , resistance to infection by strains of Pseudomonas syringae expressing the effector AvrRpt2 requires the plant resistance protein RPS2. AvrRpt2 was identified as a putative cysteine protease that results in the elimination of the Arabidopsis protein RIN4. RIN4 cleavage serves as a signal to activate RPS2-mediated resistance. AvrRpt2 is delivered into the plant cell, where it is activated by a eukaryotic factor that we identify as cyclophilin. This activation of AvrRpt2 is necessary for protease activity. Active AvrRpt2 can then directly cleave RIN4.