Abstract
RAR1-SGT1-HSP90 complex is essential for disease resistance triggered by resistance (R) proteins in plants. Recent reports showed that SGT1-HSP90 complex is also necessary for innate immunity in animals induced by R protein homologues, Nod family proteins. Here, we present the structural and functional characterization of the plant RAR1-SGT1-HSP90 complex. NMR and X-ray crystal structural analysis clarified (1) the structure of CS domain of SGT1 which binds to both RAR1 and HSP90, (2) the structure of SGT1-HSP90 core complex and (3) the structure of RAR1-SGT1-HSP90 core complex. Mutational and biochemical analyses showed that the interaction between RAR1 and SGT1 enhances the formation of RAR1-SGT1-HSP90 complex and also enhances the interaction of SGT1 to R protein. Moreover, RAR1 mutations that abrogate the interaction with SGT1 compromise resistance against virus. These results suggest that RAR1 interaction with SGT1 is a critical step for assembly and function of the RAR1-SGT1-HSP90 complex and is required for innate immunity in plants.
