Essential role of the small GTPase Rac in disease resistance of rice

Production of reactive oxygen intermediates (ROI) and a form of programmed cell death called hypersensitive response (HR) are often associated with di sease resistance of plants. We have previously shown that the Pac homolog o f rice, OsRac1, is a regulator of ROI production and cell death in rice. He re we show that the constitutively active OsRac1 (i) causes HR-like respons es and greatly reduces disease lesions against a virulent race of the rice blast fungus; (ii) causes resistance against a Virulent race of bacterial b light; and (iii) causes enhanced production of a phytoalexin and alters exp ression of defense-related genes. The dominant-negative OsRac1 suppresses e licitor-induced ROI production in transgenic cell cultures, and in plants s uppresses the HR induced by the avirulent race of the fungus. Taken togethe r, our findings strongly suggest that OsRac1 has a general role in disease resistance of rice.