Abstract
We have shown that OsRac1, a rice Rac GTPase, is involved in innate immunity. In this study we examined the functional relationships between OsRac1, and RAR1 and HSP90, two important components of R gene-mediated disease resistance. OsRAR1-RNAi plants had impaired basal resistance to the blast fungus and the virulent bacterial blight. Constitutively active OsRac1 complemented the loss of resistance, suggesting that OsRac1 and OsRAR1 are functionally linked. Co-immunoprecipitations indicate that OsRac1 forms a complex with RAR1 and HSP90 in vivo. Studies with OsRAR1-RNAi and geldanamycin, a HSP90 specific inhibitor, showed that RAR1 and HSP90 are essential for the OsRac1-mediated immune responses. Furthermore, the function of HSP90, but not RAR1, is essential for their association with OsRac1. OsRac1 also regulates RAR1 expression at both the mRNA and protein levels. Together, our results indicate that OsRac1, OsRAR1 and HSP90 form one or more complexes and play important roles in rice innate immunity.
