Abstract
Most resistance (R) genes encode nucleotide binding site-leucine-rich repeat (NBS-LRR) proteins, which act as intracellular receptors for pathogen signals. However, 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 recently found that the small GTPase OsRac1 is a molecular switch in innate immunity of rice. Therefore, we searched for OsRac1-interacting molecules by affinity column chromatography, identified five NBS-LRR-like proteins, and named them OsRac1-interacting NBS-LRR-like protein (Orin) 1-5. Orin1 preferentially bound to the GTP form of OsRac1 through its NBS domain. Agroinfiltration of the wild type Orin1 induced the hypersensitive response (HR) in Nicotiana benthamiana, whereas introduction of a dominant negative form of OsRac1 suppressed Orin1-induced HR. These results suggest that OsRac1 forms a complex with NBS-LRR-type R proteins and acts as an effector of NBS-LRR in innate immune responses.
