Activation of the small GTPase OsRac1 by an NB-LRR-type R protein plays a critical role in rice innate immunity

Abstract

Plant disease resistance (R) proteins act as intracellular receptors for sensing pathogen invasion, and trigger a variety of immune responses. However, the molecules that are activated by R proteins, and how these downstream molecules induce a variety of immune responses, are largely unknown. Here, we found that the small GTPase OsRac1 directly interacts with Pit, a nucleotide binding-leucine-rich repeat-type R protein that confers resistance to the rice blast fungus, at the plasma membrane. OsRac1 contributes to Pit-mediated reactive oxygen species production as well as the hypersensitive response, and is required for Pit-mediated disease resistance in rice. Furthermore, in vivo fluorescence resonance energy transfer experiments indicated that the active form of Pit induces the activation of OsRac1 at the plasma membrane in rice protoplasts. Thus, OsRac1 is activated by R proteins during pathogen attack, and this activation may play a critical role in R protein-mediated immunity in rice.