The Pseudomonas syringae type III effector HopK1 targets phototropins to suppress blue-light–mediated immunity
G. LI (1), N. Suetsugu (2), M. Wada (2), J. Alfano (1) (1) Center for Plant Science Innovation and the Department of Plant Pathology The University of Nebraska, U.S.A.; (2) Graduate School of Biostudies Kyoto University, Japan

Pseudomonas syringae injects effector proteins into plant cells via the type III secretion system to suppress host plant immunity. We previously showed that HopK1 uses a cleavable transit peptide to localize to chloroplasts. Here we show that HopK1 targets phototropin blue light receptors. We found that phototropin 1 and phototropin 2 were co-immunoprecipitated with the HopK1 suggesting they interact with HopK1.These results were further confirmed with yeast two-hybrid and bimolecular-fluorescence complementation (BiFC) experiments. The interaction between HopK1 and phototropin occurs in the chloroplast and cytosol. HopK1-expressing Arabidopsis plants phenocopied the phenotypes of a phot1 phot2 double mutant relating to phototropism, stomatal opening, chloroplast photorelocation movement and leaf expansion phenotypes. Moreover, phot2 and phot1phot2 mutants showed severe attenuation of plant immunity. These results suggest that blue light is important for plant immunity. While the activity of HopK1 is unknown. We found that it resembles deamidases and HopK’s contribution to virulence is dependent on the predicted deamidase catalytic site. Thus, our results suggest that that phytopathogenic bacteria evolved specific type III effectors to block the ability of plants to perceive environmental cues to promote infection.

Abstract Number: P9-278
Session Type: Poster