Abstract
Plant recognizes pathogen infection and induces a series of immune responses including hypersensitive cell death. Sekiguchi lesion (sl), one of rice lesion mimic mutants, induces cell death in the absence of pathogens. We have identified the SL gene, which encodes a CYP71 subfamilly of cytochrome P450 monooxygenase. The SL protein has the tryptamine 5-hydroxylase activity that catalyzes conversion of tryptamine to serotonin. The SL gene was up-regulated by elicitor, and treatment of serotonin into rice suspension cell induces cell death and expression of defense-related genes. These results suggested that serotonin may be a novel inducer of plant immune response. In addition, the serotonin-dependent expression of defense-related genes was partially or completely reduced in transgenic suspension cells suppressing expression of proteins contained in the OsRac1 immune complex, indicating that the components of OsRac1 complex are required for serotonin-mediated immune response.
