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Oral: Effector Biology


Xanthomonas effector kinase XopAU promotes disease symptoms by activation of host MAPKK
D. TEPER (1), E. Bosis (1), G. Popov (1), A. Girija (1), G. Sessa (2) (1) Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Israel; (2) Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Israel

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Xanthomonas euvesicatoria (Xcv) is the causal agent of bacterial spot disease of pepper. Xcv pathogenicity depends on a type III secretion system that delivers effector proteins into host cells to manipulate host signaling and promote disease. Transient expression of the Xcv effector 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 chlorotic disease symptoms. XopAU encode a catalytically active protein kinase and this activity is required for its biological function. Protein-protein interaction studies demonstrated that XopAU physically interacts with the plant immunity-associated MAPKK MKK2. In addition, MKK2 was shown to be directly phosphorylated by XopAU in vitro while expression of XopAU in planta promotes an increase in the phosphorylation of MKK2. Silencing of MKK2 or overexpression of catalytically inactive MKK2K99R in Nicotiana benthamiana reduced XopAU-mediated cell death and MAPK phosphorylation while silencing of MKK2 in pepper attenuated the Xcv-mediated chlorotic disease symptoms. Together, this study indicates that XopAU contributes to Xcv disease symptoms by manipulating host MAPK signaling through activation of MKK2.