31.ジベレリン13位水酸化に関わるイネのシトクロームP450遺伝子の解析(口頭発表)

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Two kinds of bioactive gibberellins (GAs), 13-hydroxy and non 13-hydroxy GAs are frequently found in a given plant tissue. However, physiological meaning of the GA 13-hydroxylation is still unclear. We have previously identified a cytochrome P450 gene that encodes steviol synthase (ent-kaurenoic acid 13-hydroxylase) in Arabidopsis. Transgenic Arabidopsis plants overexpressing this steviol synthase gene showed semi-dwarfism like mild GA deficient mutants. GA analysis indicated that the levels of non 13-hydroxy GAs including GA_4 were decreased, whereas those of 13-hydroxy GAs including GA_1 (which is less active in Arabidopsis) were increased in the transgenic plants. To identify rice ortholog(s) of this gene, we made transgenic Arabidopsis plants that overexpress each rice gene whose function is unknown. We found that two of these overexpressor plants show semi-dwarfism. GA analysis indicated that the endogenous GA profiles of these plants were similar to those of the overexpressor of the Arabidopsis steviol synthase gene. Using a yeast expression system, we so far found one of these recombinant rice proteins catalyzed the conversion of GA_<12> into 13-hydroxy GA_<12> (GA_<53>). These results suggest that rice has at least two cytochrome P450 genes that are involved in GA 13-hydroxylation.
2009-10-06