15. トマトのブラシノライド生合成酵素の同定

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Several cytochrome P450 monooxygenases (P450s) are involved in the biosynthesis of brassinosteroids (BRs). The oxidation at C-6 is generally essential for the biological activity of this class of hormones, and is catalyzed by P450s designated as BR C-6 oxidases. 6-deoxocastasterone (6-deoxoCS) is converted by this P450 to castasterone (CS) via a 6 α-hydroxy intermediate. The formation of brassinolide (BL) from CS requires another oxidation step (Baeyer-Villiger reaction), and a P450(s) has been thought to be involved in this reaction. The dwarf mutants of tomato are BR-deficient dwarves. Our previous work has shown that the Dwarf gene encodes a BR C-6 oxidase (CYP85A1). A null allele of this gene, extreme dwarf (d^x), causes reduced stem lengths, altered leaf morphology and a reduced fertility. Due to the block in the BR C-6 oxidation, CS and BL are not detectable, while 6-deoxoCS accumulates at a high level, in shoots of the d^x mutant. Despite such growth defects and reduced BR levels, the severe d^x mutant produces normal fruits at a low frequency. We found that BL, but not CS, accumulates at a high level in fruits of the d^x mutant. The level of 6-deoxoCS in fruits of the d^x mutant was similar to that in wild-type fruits. These results suggested the existence of an enzyme responsible for the formation of BL from 6-deoxoCS. Using a PCR-based approach, we have recently identified a P450 gene that is expressed in fruits of the d^x mutant. In this presentation, we provide evidence that this new enzyme can catalyze the formation of BL from 6-deoxoCS when expressed in yeast.
植物化学調節学会の論文
2004-10-13

15. トマトのブラシノライド生合成酵素の同定

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