Abstract
MAPK cascades play an important role in defense signaling after recognition of elicitor signals. We have isolated an elicitor-responsive MAPKK, OsMKK4 in rice, and demonstrated that a constitutive active mutant, OsMKK4DD, activates OsMPK3 and OsMPK6. This MAPK cascade induces the expression of multiple defense-related genes, cell death, diterpenoid phytoalexin biosynthesis, and phenylpropanoid biosynthesis. Using osmpk6 knock-out mutant, we demonstrated that OsMPK6 is required for the induction of cell death and regulation of gene expression by induction of OsMKK4DD. On the other hand, regulatory machinery connecting OsMKK4-OsMPK3/OsMPK6 cascade to these defense-related responses remain elusive. We are now analyzing the relationship of OsMKK4-OsMPK3/OsMPK6 cascade and several transcription factors, which possibly regulate cell death, diterpenoid phytoalexin biosynthesis or phenylpropanoid biosynthesis.
