Abstract
In rice genome, 17 putative MAPK genes are annotated but the functions of their products are largely unknown. OsMPK2 is the rice ortholog of tobacco SIPK. SIPK and AtMPK6 are activated by SA and pathogen infection, and regulate stress-responsive ethylene production. OsMPK2 is activated by elicitors as is SIPK but not clearly activated by SA. Moreover, in cell culture of osmpk2 knock-out mutant, expression of defense-related genes such as PR10a was up-regulated as compared with wild type. After treatment with elicitor or BTH, PR10a expression increased more strongly and rapidly in mutant cells. These results suggested that OsMPK2 negatively regulates the expression of defense-related genes. To clarify the role of OsMPK2 in defense mechanism, we are analyzing other components of OsMPK2 signaling pathway, such as MAPK kinase and rice ortholog of AtACS2, which is the rate-limiting enzyme of ethylene biosynthesis and a substrate of AtMPK6.
