Phosphorylation of rice RBOH by CERK1-associated RLCK regulates chitin-triggered ROS burst
M. YOSHIOKA (1), K. Yamaguchi (2), M. Fujiwara (3), S. Yoshimura (2), T. Kawasaki (2), H. Yoshioka (1) (1) Nagoya University, Japan; (2) Kindai University, Japan; (3) Keio University, Japan

A rice multimeric chitin receptor complex composed of OsCEBiP and OsCERK1 associates with OsRLCK185 (Oryza sativa receptor-like cytoplasmic kinase 185) that phosphorylates targets required for immune responses. OsRLCK185 is the substrate of OsCERK1, and regulates chitin- and PGN-induced immune responses. After chitin sensing, OsCERK1 phosphorylates OsRLCK185, and releases activated OsRLCK185 from the receptor complex. This dissociation contributes to the activation of MAP kinases and ROS (reactive oxygen species) burst. The NADPH oxidase, RBOH (respiratory burst oxidase homolog), has a central role in ROS burst in plants. We found that transient expression of OsRBOHI with OsRLCK185 induces ROS burst in Nicotiana benthamiana leaves. Chitin-triggered ROS burst was markedly suppressed in OsRBOHI-RNAi rice cells and transgenic rice leaves. We identified OsRLCK185-mediated phosphorylation sites of N-terminal region of the recombinant OsRBOHI by LC-MS/MS analysis. We generated various N-termini of OsRBOHI peptides with alanine substitutions at the phosphorylated serines. In vitro phosphorylation analysis using these peptides indicated that these serines are phosphorylated by OsRLCK185. Furthermore, co-expression of these alanine-substituted mutants of OsRBOHI with OsRLCK185 in N. benthamiana leaves showed marked reduction of ROS burst. Thus, N-terminal region of OsRBOHI could be directly phosphorylated by OsRLCK185, resulting in ROS burst.

Abstract Number: P17-644
Session Type: Poster