红豆杉科及三尖杉科的分子系统发育——兼论竹柏属的系统位置

Chloroplast matK gene phylogeny of Taxaceae and Cephalotaxaceae, with additional reference to the systematic position of Nageia

测定了红豆杉科、三尖杉科、罗汉松科及松科共 9属 1 3种植物的matK基因序列 ,发现 3′端的单碱基插入造成matK基因在这些类群间有较大的长度变异 ( 1 488～ 1 548bp) ,其它插入或缺失的长度为 3、6或 9bp(白豆杉中有一个长为 2 7bp的缺失 ) ,且绝大多数插入或缺失事件具有系统发育信息。matK基因中 ,密码子第 1、2及 3位的变异率较为相近 ,平均同义替代率约为平均非同义替代率的 2倍。以松科2属 3种植物为外类群 ,运用PAUP软件进行的系统发育分析仅得到一棵最简约树 (步长为 895,CI =0 850 ,RI=0 876) ,该简约树的各分支均得到bootstrap分析的极强支持。结果表明 :红豆杉科与三尖杉科均为单系群 ,二者互为姐妹群 ;白豆杉属与穗花杉属为红豆杉科中两个很自然的属 ,白豆杉属为红豆杉属的姐妹群 ,穗花杉属为榧树属的姐妹群。竹柏属与罗汉松属聚为一支 ,二者间的亲缘关系得到boot strap分析的 1 0 0 %支持 ,从分支分类学及遗传距离角度 ,作者不赞同将竹柏属提升为科。

Reported in the present paper is a robust chloroplast matK gene phylogeny of Taxaceae, Cephalotaxaceae and Podocarpaceae represented by 10 species of seven genera, with three species of the Pinaceae as outgroups. The matK length of the 13 species ranges from 1488 bp to 1548 bp, which results from indels, in particular,1 bp(base pair) insertion near the 3′ end of the gene in some groups. A 27 bp deletion was found at the nucleotide position 213 from the 5′ end of the matK gene of Pseudotaxus chienii. The aligned sequences used in PAUP and MEGA analyses were 1568 bp and 1494 bp respectively. In the matK gene, the rates of variation at the first, second and third codon positions are similar although the mean frequency of synonymous substitution is approximately twice as high as that of nonsynonymous substitution. Branch and Bound search found only one most parsimonious tree (tree length=895, CI= 0 850 , RI=0 876), in which all clades were strongly supported by bootstrap test. According to the tree, Taxaceae and Cephalotaxaceae are monophyletic groups, and the sister group relationship between the two families was confirmed. Taxus is closely related to Pseudotaxus while Torreya is the sister group of Amentotaxus. In addition, the close relationship between Nageia and Podocarpus was resolved. The present study supports the generic status of Pseudotaxus and Amentotaxus in point of cladistic analysis and genetic distance, but contradicts the establishment of the family Nageiaceae.