β-胡萝卜素异构酶（D27）是独脚金内酯（SLs）合成通路的第一个酶。该研究以普通小麦‘中国春’为材料，通过RT-PCR克隆了小麦β-胡萝卜素异构酶对应cDNA（TaD27），并对其在不同组织和低磷胁迫下的表达进行分析。结果显示：（1）克隆获得2个高度同源cDNA片段，分别定位于7A、7D 染色体的长臂，命名为 TaD27-7A L和TaD27-7DL ；序列分析发现，7B染色体长臂上还存在另一个同源基因 TaD27-7BL。（2）3个 TaD27基因均包含7个外显子，编码区长度分别为828 bp（7AL）、840 bp（7BL）和843 bp（7DL），编码蛋白的 N-端均含有叶绿体转运肽；进化分析表明，植物D27蛋白主要聚集在3个进化枝中，小麦、水稻和玉米等单子叶植物的D27高度同源，聚集在同一进化分枝。（3）组织表达分析表明，T aD27基因在叶、叶鞘和茎中的表达量较高，在幼穗中的表达量相对较低，在根中的表达量最低；低磷胁迫下，T aD27在根中的表达量先下降后升高，胁迫至6～12 h时，表达量达到最低，96 h时基本恢复至初始状态，而在叶中表达量则是先升高后下降，6 h达到峰值，12 h基本恢复到初始水平，随后表达量继续下降。%β-carotene isomerase (D27) is the first enzyme involved in strigolactones biosynthesis .In this study ,the cDNAs encoding β-carotene isomerase (TaD27) were cloned from wheat cultivar Chinese Spring by RT-PCR .Further ,their expression in different tissues and under low phosphate stress were analysed by Real-time Quantitative PCR .The result showed that :(1) Two TaD27 cDNAs were cloned ,which was maped on the long arms of 7A and 7D chromosome ,respectively (named TaD27-7A L and TaD27-7DL) . In addition ,we found another locus located on chromosome 7BL encoding the third homolog (TaD27-7BL) by sequence analysis .(2) Each of the three TaD27s contains 7 exons composing an ORF of 828 bp (7AL) ,840 bp(7BL) or 843 bp (7DL) ,respectively and encodes a protein containing a chloroplast transit peptide at N-terminal .Phylogenetic analyses indicated that D 27s in plants clustered into three independent clades .TaD27s share a high level of identity with orthologs in other monocots such as Oryza sativa and Zea mays ,as a result ,they are clustered in the same clade .(3) The expression level of TaD27 is relative-ly high in leaves ,sheaths and stems ,lower in young panicles ,and lowest in roots .Under low phosphate stress the expression of T aD27 in roots is dow n regulated to the bottom in 6-12 h firstly ,and then it rises to the normal level after 96 h .On the contrary ,the expression of TaD27 in leaves is up regulated in early stage and the peak is at 6h ,then it continuously drops to a relatively low point at 96 h .
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