十字花科植物SAMDC基因同源序列的克隆与进化分析

Cloning and evolutionary analysis of homologous sequences of SAMDC gene in Cruciferae

腺苷甲硫氨酸脱羧酶（SAMDC）是参与植物多胺合成的一个关键酶。根据GenBank中已报道的SAMDC基因编码序列保守区域设计特异引物，运用PCR技术分另4从十字花科6属14个物种中新克隆分离了SAMDC基因的同源序列。比较分析结果表明：这些同源序列的相似性达87％以上，所推导的氨基酸序列相似性达90％以上，且两者种间差异分别为0．2％～10．1％和0．3％～6．6％，属间差异除“圆白”萝卜外分别是4．9％。13．6％和3．1％～10.3％；SAMDC基因的核苷酸及其可能编码的氨基酸序列差异属间较种间大，可用于属间的分类等级研究；且氨基酸序列间的差异比核苷酸序列间的差异小的多，因而根据核苷酸序列构建了NJ与ME分子系统树．进化树直观地表明在亲缘进化关系上芸薹属与萝卜属较近，其他依次为山芥属、萍菜属、拟南芥属，与荠菜属最远。研究结果有助于从分子水平阐明十字花科植物间的亲缘进化关系，可为其种质资源利用提供理论依据。

S-adenosylmethionine decarboxylase activity （SAMDC） is a key enzyme involved in biosynthesis of the polyamines, viz. spermidine and spermine. In the present study, SAMDC gene analogues from 14 species of 6 genera in Cruciferae were obtained by PCR strategy using specific primers designed from conserved regions of SAMDC gene reported in the GenBank. The phylogenetic relationships of these species belonging to the family Cruciferae were investigated through comparison of the genes. Homologous sequences of SAMDC comparison indicated that the similarities among the genes at nucleotide and amino acid levels were over 87% and 90%, respectively. The differences in genes at nucleotide and amino acid levels between species ranged from 0.2 % to 10.1% and 0.3% to 6.6%, respectively, while those between genera except Raphanus were 4.9 % to 13.6 % and 3.1% to 10.3%, respectively. The differences of sequences of nucleotides and amino acids among genera were higher than those among species, and the differences of nucleotides sequences were higher than those of amino acids. The phylogenetic tree was thus constructed based on the alignment nucleotides sequences from Nei＇s genetic distances. The neighbor-joining （NJ） and minimum-evolution （ME） trees showed that Brassica was closely related to Raphanus, followed by Barbarea, Roripl Scop and Arabidopsis Heynh, but was remotely related to Capsella Medic. This research elucidated the relationship among crucifer species at nucleotide level, which could proved some help for the utilization of plant germplasms.