Xanthomonas XopAU is an active protein kinase that manipulates host MAP kinase signaling to promote disease
G. SESSA (1), D. Teper (2), E. Bosis (2), G. Popov (2), G. Popov (2) (1) Tel Aviv University, Israel; (2) Tel Aviv University, Israel

The Gram-negative bacterium Xanthomonas euvesicatoria (Xe), is the causal agent of spot disease in pepper and tomato plants. Xe pathogenicity depends on a type III secretion system (T3S) that translocates effector proteins into the plant cell. We identified a novel Xe effector, XopAU, that encodes a Ser/Thr protein kinase and plays a role in Xe pathogenicity. Transient expression of XopAU in host and non-host plants promoted typical defense responses including phosphorylation of MAPKs, accumulation of pathogenesis-related (PR) proteins and elicitation of cell death. Genetic analysis of XopAU by insertional mutagenesis and overexpression revealed a role for this effector in the development of disease symptoms in pepper plants. XopAU was shown in vitro to encode a catalytically active protein kinase whose activity is required for its biological function. Protein-protein interaction studies demonstrated that XopAU physically interacts with and phosphorylates the immunity-associated MAPKK MKK2. Expression of XopAU in planta resulted in enhanced MKK2 phosphorylation at several residues including a Ser and Thr in the MKK2 kinase activation loop. In addition, silencing of MKK2 in N. benthamiana plants reduced XopAU-mediated cell death and MAPK phosphorylation further supporting the notion that MKK2 represents a target for XopAU in the host plant. Together, this study indicates that XopAU contributes to Xe disease symptoms in pepper plants by manipulating host MAPK signaling though phosphorylation and activation of MKK2.

Abstract Number: P9-304
Session Type: Poster