Abstract
Most resistance (R) genes encode nucleotide binding site-leucine-rich repeat (NBS-LRR) proteins, which act as intracellular receptors for pathogen signals. It is largely unknown how NBS-LRR resistance proteins transduce pathogen signals to their downstream effectors and thereby execute innate immunity in plants. We have previously found that the small GTPase OsRac1 plays critical roles in R gene-mediated defense response in rice. Therefore, we searched for OsRac1-interacting molecules and found that OsRac1 directly interacted with Pit, Pib, Pi9 and Xa1 which are NBS-LRR-type R proteins for rice blast and rice bacterial blight. An expression of dominant negative form of OsRac1 suppressed Pit-mediated defense response against rice blast fungus. An active form of Pit activated the OsRac1 activity in rice protoplasts. These results suggest that OsRac1 forms a complex with R proteins and acts as a downstream effector of R proteins, thereby contributing defense signaling in rice.
