Molecular analysis of the defensome protein complex containing RacGTPase which plays a key role in defense signaling of rice

Abstract

We have previously shown that OsRac1, a small GTPase Rac of rice, is involved in disease resistance. In this study, we find that RAR1, an important component of R gene mediated disease resistance, HSP90 and 70, the molecular chaperones, MAPK6, a rice MAPK homologous to tobacco NtSIPK and Arabidopsis MAPK6 and Sti1 (Hop in mammalian cells) are all found in OsRac1 complex. Functional studies of RAR1, Sti1 and HSP90 using RNAi method and geldanamycin (GDA), the HSP90 specific inhibitor, indicate that they have critical role in rice innate immunity and involve in OsRac1 related defense signaling pathway. On the other hand, treatment of GDA but not suppression of RAR1 disassociates OsRac1 protein complex, indicating that HSP90 but not RAR1 function is required for the complex formation. Together, our results suggest a key role of OsRac1 protein by forming the defensome with important components in the early steps of defense signaling.