Regulation of OsRac1 mRNA Against Defense-Related Stimuli in Wild-Type Rice Seedlings

A rice (Oryza sativa L.) homolog of mammalian Rac-GTPase, OsRac1, characterized only in transgenic rice, was proposed to involve in cell death/disease resistance. However, its role in wild-type rice remains uncharacterized and unclear. We examined expression of the OsRac1 mRNA in response to stress signalling components, jasmonic acid (JA), hydrogen peroxide (H2O2), and two protein phosphatase inhibitors, cantharidin (CN) and endothall (EN), using rice (cv. Nipponbare) seedlings. The OsRac1 transcript, whose accumulation required certain de novo synthesized protein factor(s), increased in the leaves upon CN/EN and H2O2 treatment, but not by JA. Using two pathogenesis-related (PR) protein gene markers, OsPR5 and OsPR10, our results also reveal OsRac1 mRNA accumulates later than that of these two important defense/stress-related OsPR genes.