Jager Corinne E, Symons Gregory M, Nomura Takahito, Yamada Yumiko, Smith Jennifer J, Yamaguchi Shinjiro, Kamiya Yuji, Weller James L, Yokota Takao, Reid James B
School of Plant Science, University of Tasmania, Tasmania 7005, Australia.
Plant Physiol. 2007 Apr;143(4):1894-904. doi: 10.1104/pp.106.093088. Epub 2007 Feb 23.
C-6 oxidation genes play a key role in the regulation of biologically active brassinosteroid (BR) levels in the plant. They control BR activation, which involves the C-6 oxidation of 6-deoxocastasterone (6-DeoxoCS) to castasterone (CS) and in some cases the further conversion of CS to brassinolide (BL). C-6 oxidation is controlled by the CYP85A family of cytochrome P450s, and to date, two CYP85As have been isolated in tomato (Solanum lycopersicum), two in Arabidopsis (Arabidopsis thaliana), one in rice (Oryza sativa), and one in grape (Vitis vinifera). We have now isolated two CYP85As (CYP85A1 and CYP85A6) from pea (Pisum sativum). However, unlike Arabidopsis and tomato, which both contain one BR C-6 oxidase that converts 6-DeoxoCS to CS and one BR C-6 Baeyer-Villiger oxidase that converts 6-DeoxoCS right through to BL, the two BR C-6 oxidases in pea both act principally to convert 6-DeoxoCS to CS. The isolation of these two BR C-6 oxidation genes in pea highlights the species-specific differences associated with C-6 oxidation. In addition, we have isolated a novel BR-deficient mutant, lke, which blocks the function of one of these two BR C-6 oxidases (CYP85A6). The lke mutant exhibits a phenotype intermediate between wild-type plants and previously characterized pea BR mutants (lk, lka, and lkb) and contains reduced levels of CS and increased levels of 6-DeoxoCS. To date, lke is the only mutant identified in pea that blocks the latter steps of BR biosynthesis and it will therefore provide an excellent tool to further examine the regulation of BR biosynthesis and the relative biological activities of CS and BL in pea.
C-6氧化基因在植物生物活性油菜素内酯（BR）水平的调控中起关键作用。它们控制BR的激活，这涉及将6-脱氧卡甾酮（6-DeoxoCS）C-6氧化为卡甾酮（CS），在某些情况下还涉及CS进一步转化为油菜素内酯（BL）。C-6氧化由细胞色素P450的CYP85A家族控制，迄今为止，已在番茄（Solanum lycopersicum）中分离出两个CYP85A，在拟南芥（Arabidopsis thaliana）中分离出两个，在水稻（Oryza sativa）中分离出一个，在葡萄（Vitis vinifera）中分离出一个。我们现在从豌豆（Pisum sativum）中分离出两个CYP85A（CYP85A1和CYP85A6）。然而，与拟南芥和番茄不同，拟南芥和番茄都含有一种将6-DeoxoCS转化为CS的BR C-6氧化酶和一种将6-DeoxoCS直接转化为BL的BR C-6贝耶尔-维利格氧化酶，豌豆中的两种BR C-6氧化酶主要作用都是将6-DeoxoCS转化为CS。在豌豆中分离出这两个BR C-6氧化基因突出了与C-6氧化相关的物种特异性差异。此外,我们分离出了一个新的BR缺陷型突变体lke，它阻断了这两个BR C-6氧化酶之一（CYP85A6）的功能。lke突变体表现出一种介于野生型植物和先前鉴定的豌豆BR突变体（lk、lka和lkb）之间的表型，并且CS水平降低，6-DeoxoCS水平升高。迄今为止，lke是在豌豆中鉴定出的唯一阻断BR生物合成后期步骤的突变体，因此它将为进一步研究豌豆中BR生物合成的调控以及CS和BL的相对生物活性提供一个极好的工具。
