咖啡碱是茶叶中重要的功能成分,它以黄苷为底物,以S-腺苷甲硫氨酸（SAM）为甲基供体,通过N-甲基转移酶（NMT）类催化的一系列甲基化反应合成的产物。根据NMT基因高度相似的特性,利用长片段PCR法和侧翼序列克隆技术分离了白叶一号6种NMTs的基因组DNA全长,其中有2种为已报道的茶树咖啡碱合成酶基因TCS1、TCS2,1种为假基因,另3种基因分别被命名为TCS3、TCS4、TCS5,基因结构分析发现这6种基因均由4个外显子和3个内含子组成。山茶属植物的NMTs可聚为5类,其中TCS4和TCS5为与其他基因的相似性相对较低的一类。这些结果为今后更好地从基因组水平上剖析茶树咖啡碱的遗传机制提供有用参考。
Caffeine is an important bioactive compound in tea. It is synthesized from xanthosine catalysed by N-methyltransferase (NMT) that using S-adenosylmethionine (SAM) as the methyl donor. Based on the characterization of high similarity of CS (Caffeine Synthase) gene sequences, 6 NMTs were cloned from Baiye 1 by using the technique of long PCR and cloning flanking DNA sequence. Two of them are TCS1 and TCS2, one is a pseudogene, and the other three are named TCS3, TCS4 and TCS5, respectively. It was found that these genes were all composed by four exons and three introns through analysis of gene structure. The NMTs of Camellia plants were clustered into 5 groups, the similarity of TCS4 and TCS5 between with other genes is lower. These results provided useful references to dissect the genetic mechanism of caffeine from genome level in tea plant for the future.
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