Abstract
MAP kinase cascades play an important role in defense signaling after recognition of PAMPs signals. In rice, OsMPK6 is strongly activated by elicitor treatment but signal cascade downstream of OsMPK6 is still unknown. To analyze defense responses regulated by MPK pathway, we focused on the upstream MAPKK, OsMKK4.
Accumulation of constitutive active form of OsMKK4 (OsMKK4DD) activated several MPKs and induced cell death. We identified OsMPK6 as a target of OsMKK4. Microarray analysis showed that many defense-related genes, such as ethylene, phytoalexin or phenylpropanoids synthesis, are up-regulated by accumulation of OsMKK4DD, indicating that OsMKK4 is a positive regulator of defense signaling in rice. Because elicitor treatment also induces expression of second metabolite synthesis genes, we are comparing signal cascades mediated by OsMKK4DD and elicitor treatment. To clarify the function of OsMPK6 in these signal cascades, we are also analyzing defense responses in osmpk6 mutant.
