60. シロイヌナズナのUGT73C5はブラシノステロイドをグルコシル化する

概要

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Steroid hormones play essential roles in growth and development, and the precise control of their homeostasis is a prerequisite for normal growth. UDP-glycosyltransferases (UGTs) are considered to play an important regulatory role in the activity of steroids in mammals and insects. This study describes the first functional characterization of a UGT that accepts plant steroid hormones, brassinosteroids (BRs) as substrates. The UGT73C5 of Arabidopsis thaliana catalyses the 23-O-glucosylation of BRs, brassinolide (BL) and castasterone. Transgenic plants over-expressing UGT73C5 display a BR-deficient phenotype and contain reduced amounts of BRs. The phenotype, which was already apparent in seedlings, could be rescued to wild type by application of BR. In feeding experiments with BL, wild-type seedlings converted BL to the 23-O-glucoside. Overexpression of the UGT73C5 led to accumulation of BL-23-O-glucoside, whereas silencing the gene resulted in undetectable levels of the glucoside. The levels of the BL-23-O-glucosides were two orders-of-magnitude higher in the over-expressing lines compared to wild type. These data support the hypothesis that 23-O-glucosylation of BL is a function of UGT73C5 in planta and that glucosylation regulates BR activity.
植物化学調節学会の論文
2005-10-13