Multiple Xanthomonas euvesicatoria type III effectors inhibit flg22-triggered immunity
G. POPOV (1), M. Fraiture (2), F. Brunner (2), G. Sessa (3) (1) Department of Molecular Biology and Ecology of Plants, Tel-Aviv University, Israel; (2) Department of Biochemistry, Centre for Plant Molecular Biology, Eberhard Karls University, Germany; (3) Department of Molecular Biology and Ecology of Plants, Tel-Aviv University, Israel

Xanthomonas euvesicatoria (Xe) is the causal agent of bacterial spot disease in pepper and tomato. Xe bacteria interfere with plant cellular processes by injecting effector proteins into host cells through the type III secretion (T3S) system. About 35 T3S effectors have been identified in the Xe strain 85-10 and a few of them were implicated in suppression of pattern-triggered immunity (PTI). We used an Arabidopsis thaliana pathogen-free protoplast-based assay to identify Xe 85-10 effectors that interfere with PTI signaling induced by the bacterial peptide flg22. Of 33 tested effectors, 17 inhibited activation of a flg22-inducible promoter. Among them, 9 effectors also interfered with activation of an ABA-inducible promoter. However, effectors that inhibited flg22-induced signaling did not affect phosphorylation of mitogen-activated protein (MAP) kinases acting downstream of flg22 perception. The effectors XopF1, XopF2, XopE2, XopAP, XopAE, XopH, and XopAJ inhibited flg22-induced callose deposition in planta and, except for XopF1, also enhanced disease symptoms caused by attenuated Pseudomonas syringae bacteria. Finally, selected effectors were found to localize to various plant subcellular compartments. These results indicate that Xe bacteria utilize multiple T3S effectors to suppress flg22-induced signaling acting downstream or in parallel to MAP kinase cascades and suggest they act through different molecular mechanisms.

Abstract Number: P7-201
Session Type: Poster