59.イネのファイトカサン生合成酵素遺伝子クラスターに存在するP450遺伝子の機能解析(口頭発表)

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Antimicrobial diterpenoid compounds such as momilactones and phytocassanes are major phytoalexins produced in rice upon pathogen attack. Previously, we reported that the momilactone biosynthetic genes are clustered in rice chromosome 4 and are coexpressed after the elicitation. Moreover, we showed that a novel gene cluster for phytocassane biosynthesis is organized in rice chromosome 2, which consists of two diterpene cyclase genes for phytocassanes (OsCPS2 and OsKSL7) and six cytochrome P450 monooxygenase (P450) genes (CYP71Z6, CYP71Z7, CYP76M5, CYP76M6, CYP76M7 and CYP76M8). RNAi experiment has revealed that CYP71Z7 is involved in biosynthesis of phytocassanes A, B and D (C-2 oxygenated phytocassanes). In this report, we found that some RNAi lines, in which expression of CYP76M7 and CYP76M8 were suppressed, exhibited impaired production of phytocassanes B, C and E (C-1 oxygenated phytocassanes), whereas accumulated levels of phytocassanes A and D, and 1-deoxyphytocassane C (C-1 non-oxygenated phytocassanes) were comparable to those of wild-type plants. Since CYP76M7 was shown to catalyze C-11 hydroxylation of phytocassanes, the above results suggest that CYP76M8 is likely to be involved in C-1 hydroxylation steps in the phytocassane biosynthesis. In addition to that, this RNAi plants showed lesionmimic phenotypes. We are now studying a relationship between lesion mimic and phytoalexin production in RNAi plants.
2010-10-01