Regulation of the Rice NADPH Oxidase by Binding of Small GTPase Rac and Ca2+ to Its N-terminal Extension
In this study, using yeast two-hybrid and in vitro binding assays, we found that the CA-OsRac1, but not the dominant negative form, interacted with the N-terminus of OsrbohB. The N-terminus contained two Ca2+-binding EF-hand motifs, was sufficient for OsRac1- OsrbohB interaction. Fluorescence resonance energy transfer microscopy showed that OsRac1 interacted with the N-terminus of OsrbohB predominantly in the GTP-bound form in vivo and the interaction was suppressed by cytosolic Ca2+ ions accumulation. Furthermore, in vitro NADPH oxidase activity assay also showed that GTP-bound OsRac1 enhanced NADPH oxidase activity and the activity was suppressed by Ca2+ ions.