Studies on regulation mechanism of diterpenoid phytoalexin biosynthesis and its evolutional aspects

Abstract

Cultivated rice （Oryza sativa） produces many types of diterpene phytoalexins, such as momilactones and phytocassanes as antimicrobial substances.　It is known that the biosynthetic genes are clustered on rice chromosomes and co-expressed in response to environmental stimuli. We demonstrated that expressions of the clustered genes and the upstream MEP pathway genes are coordinately regulated by transcription factors inductively expressed under stress conditions.　Comparative genomics and biochemical studies using wild rice species not only have shown when and how rice plants acquired the ability to co-ordinately produce phytoalexins, but also how evolutionary events led to the clustering of the biosynthetic genes.　Interestingly, bryophyte moss and paddy weeds barnyardgrass were also shown to inductively produce momilactones upon environmental stresses and that they possess the gene cluster.　The results imply that a chemical defense system using momilactones appears to be maintained in diverse plant species as a consequence of convergent evolution.