Abstract
Momilactones and phytocassanes are major phytoalexins in rice. We showed that biosynthetic genes for momilactones are clustered on rice chromosome 4, and that those for phytocassanes are clustered on rice chromosome 2. We also succeeded in identification of a bZIP transcription factor OsTGAP1 that coordinately regulates the expression of all the momilactone biosynthetic genes in the cluster. Here we report that OsTGAP1 is also involved in the expression of the MEP pathway genes (OsDXS3, OsDXR, OsCMS) and phytocassane biosynthetic genes (OsCPS2, OsKSL7). Inductive expression of OsCPS2 and OsKSL7 after treatment with a chitin oligosaccharide elicitor in wild-type cells was weakened in ostgap1 mutant cells. In contrast, OsTGAP1 over-expressing lines exhibited enhanced expression of OsCPS2 and OsKSL7 in response to the elicitor. We also found that the elicitor-induced expression of OsDXS3, OsDXR and OsCMS was significantly suppressed in the ostgap1 mutant cells and that OsTGAP1 over-expressing lines exhibited enhanced expression of these genes. These results indicate that OsTGAP1 is a master transcription factor regulating the inductive production of diterpenoid phytoalexins in rice.
