Cloning and characterization of a cabbage <i>BoAOS</i> gene with enhanced drought tolerance

Allene oxide synthase (<i>AOS</i>), which is a cytochrome P450 (<i>CYP74A</i>), catalyses the first step in the biosynthesis of jasmonic acid from lipoxygenase-derived hydroperoxides of free fatty acids. The full-length cDNA of an <i>AOS</i>-like gene was cloned from <i>Brassica oleracea</i> using rapid amplification of cDNA ends and was designated as <i>BoAOS</i>. The <i>BoAOS</i> expression level was higher in alabastrums and flowers than in other tissues of cabbage, as determined by real-time reverse transcription polymerase chain reaction (RT-PCR). To characterize the <i>BoAOS</i> gene, <i>Arabidopsis</i> was transformed via <i>Agrobacterium tumefaciens</i> with a vector to express the gene under the control of a strong constitutive promoter, CaMV35S (Cauliflower Mosaic Virus). Based on analyses of tolerance to drought stress, compared with control plants, the overexpression of <i>BoAOS</i> in transgenic plants increased the endogenous jasmonic acid level and conferred higher tolerance to drought stress. Therefore, we suggest that <i>BoAOS</i> may be a suitable candidate gene to produce transgenic plants with tolerance to drought stress.丙二烯氧化物合酶（Allene oxide synthase, AOS）属于细胞色素P450（cytochrome P450）家族的CYP74A亚家族成员，可催化以脂氧合酶衍生的游离脂肪酸氢过氧化物为底物合成茉莉酸（jasmonic acid）的第一步反应。研究人员采用cDNA末端快速扩增技术（rapid amplification of cDNA ends, RACE）从甘蓝（Brassica oleracea）中克隆得到一个AOS同源基因的全长互补脱氧核糖核酸（complementary DNA, cDNA），并将其命名为BoAOS。通过实时反转录聚合酶链式反应（real-time reverse transcription polymerase chain reaction, RT-PCR）检测发现，BoAOS在甘蓝的花蕾与花中的表达水平显著高于其他组织。为解析BoAOS基因的功能，研究人员构建了由组成型强启动子花椰菜花叶病毒35S（Cauliflower Mosaic Virus 35S promoter, CaMV35S）驱动BoAOS表达的载体，并通过根癌农杆菌（Agrobacterium tumefaciens）介导转化拟南芥（Arabidopsis）。干旱胁迫耐受性分析结果显示，与对照植株相比，转BoAOS基因植株中BoAOS的过表达可提升内源茉莉酸水平，并赋予植株更强的干旱胁迫耐受性。综上，本研究认为BoAOS可作为培育抗旱转基因植株的优良候选基因。