Abstract
Plants that are attacked by pathogenic microorganisms respond with a variety of defense reactions including production of phytoalexins. In rice, the five enzyme genes (OsCPS4, OsKSL4, CYP99A2, CYP99A3, and OsMAS) that form a gene cluster on chromosome 4 are involved in biosynthesis of the diterpenoid phytoalexins momilactones. These enzyme genes are co-ordinately induced by chitin origosaccharide elicitor treatment in cultured-rice cells. To elucidate regulatory mechanisms for the co-ordinate expression of the genes, we previously performed OsKSL4 promoter analysis followed by identification of OsTGA1 as a bZIP-type transcription factor that regulates OsKSL4 elicitor-responsiveness. Microarray analysis using Ostga1 mutants suggested that OsTGA1 regulates not only OsKSL4 but also other momilactones biosynthetic genes. In this study, we generated OsTGA1-overexpressing mutants, and found that the cluster-forming genes including OsKSL4 are constitutively expressed in the mutants. It was also shown that momilactones are constitutively produced at higher levels in the mutants than wild-type rice cells.
