The last reaction producing brassinolide is catalyzed by cytochrome P-450s, CYP85A3 in tomato and CYP85A2 in Arabidopsis
The last reaction producing brassinolide is catalyzed by cytochrome P-450s, CYP85A3 in tomato and CYP85A2 in Arabidopsis
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DOI：
10.1074/jbc.m414592200
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发表时间：
2005-05-06
影响因子：
4.8
通讯作者：
Yamaguchi, S
中科院分区：
文献类型：
--
作者：
Nomura, T;Kushiro, T;Yamaguchi, S
油菜素类固醇是植物生长发育所必需的甾体激素。油菜素内酯是最具生物活性的油菜素类固醇，具有七元内酯环，由其直接前体蓖麻酮的拜尔-维利格氧化形成。尽管油菜素内酯合酶在控制植物发育方面具有潜在的关键作用，但尚未得到鉴定。先前的研究表明，细胞色素 P-450 单加氧酶 CYP85A 家族成员可催化从 6-脱氧卡斯特酮形成卡斯特酮。番茄矮化 (CYP85A1) 基因的无效突变，即极端矮化 (d(x))，会因油菜素类固醇缺乏而导致严重矮化，但 dx 突变体仍能结出果实。在这里，我们发现 dx 果实中的油菜素内酯含量高于野生型果实，并且新的 CYP85A 基因 CYP85A3 优先在番茄果实中表达。番茄 CYP85A3 催化拜尔-维利格氧化反应，从酵母中的卡斯特酮产生油菜素内酯，同时将 6-脱氧卡斯特酮转化为卡斯特酮。我们还表明，最初被定性为卡斯特酮合酶的拟南芥 CYP85A2 也具有油菜素内酯合酶活性。将卡斯特酮和油菜素内酯外源应用于拟南芥 cyp85a1/cyp85a2 双突变体表明卡斯特酮可以作为活性油菜素类固醇发挥作用，但其转化为油菜素内酯对于拟南芥的正常营养发育是必需的。我们假设卡斯特酮是番茄营养生长过程中主要的活性油菜素类固醇，而油菜素内酯可能在该物种的果实发育中发挥器官特异性作用。
Brassinosteroids are steroidal hormones essential for the growth and development of plants. Brassinolide, the most biologically active brassinosteroid, has a seven-membered lactone ring that is formed by a Baeyer-Villiger oxidation of its immediate precursor castasterone. Despite its potential key role in controlling plant development, brassinolide synthase has not been identified. Previous work has shown that the formation of castasterone from 6-deoxocastasterone is catalyzed by members of the CYP85A family of cytochrome P-450 monooxygenases. A null mutation in the tomato Dwarf (CYP85A1) gene, extreme dwarf (d(x)), causes severe dwarfism due to brassinosteroid deficiency, but the dx mutant still produces fruits. Here, we show that dx fruits contain brassinolide at a higher level than wild-type fruits and that a new CYP85A gene, CYP85A3, is preferentially expressed in tomato fruits. Tomato CYP85A3 catalyzed the Baeyer-Villiger oxidation to produce brassinolide from castasterone in yeast, in addition to the conversion of 6-deoxocastasterone to castasterone. We also show that Arabidopsis CYP85A2, which was initially characterized as castasterone synthase, also has brassinolide synthase activity. Exogenous application of castasterone and brassinolide to the Arabidopsis cyp85a1/cyp85a2 double mutant suggests that castasterone can function as an active brassinosteroid but that its conversion into brassinolide is necessary for normal vegetative development in Arabidopsis. We postulate that castasterone is the major active brassinosteroid during vegetative growth in tomato, whereas brassinolide may play an organ-specific role in fruit development in this species.