91 新規ブラシノステロイド生合成経路の解明

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The natural occurrence of brassinosteroid (BRs) in cultured Catharanthus roseus cells and in Arabidopsis seedlings was investigated. Using GC-MS analysis, 22-hydroxylated BRs such as (22S)-22-hydroxycampesterol (22-OHCR), (22S, 24R)-22-hydroxyergost-4-en-3-one (22-OH-4-en-3-one), (22S, 24R)-22-hydroxy-5α-ergostan-3-one (22-OH-3-one), and 6-deoxocathasterone (6-DeoxoCT) were identified. Metabolic experiments with [^2H_6]22-OHCR were performed in cultured C. roseus cells and Arabidopsis seedlings (wild type and det2), and the metabolites were analyzed by GC-MS. In both C. roseus cells and wild-type Arabidopsis seedlings, [^2H_6]22-OH-4-en-3-one, [^2H_6]22-OH-3-one, and [^2H_6]6-DeoxoCT were identified as metabolites of [^2H_6]22-OHCR, while the major metabolite in det2 seedlings was [^2H_6]22-OH-4-en-3-one. Analysis of endogenous levels of these BRs revealed that det2 accumulates 22-OH-4-en-3-one. The levels of downstream compounds were remarkably reduced compared to the wild type. Exogenously applied 22-OH-3-one and 6-DeoxoCT were found to rescue det2 mutant phenotypes, while 22-OHCR and 22-OH-4-en-3-one did not. These results substantiate the existence of a new subpathway (22-OHCR -> 22-OH-4-en-3-one -> 22-OH-3-one -> 6-DeoxoCT), and reveal that the det2 mutant is defective in the conversion of 22-OH-4-en-3-one to 22-OH-3-one, which leads to brassinolide biosynthesis.
植物化学調節学会の論文
2002-10-31