16种环节动物线粒体基因排列、特征比较及系统发育分析

Gene Order,Characteristics and Phylogenetic Analysis of Mitochondrial Genomes in Sixteen Members in Annelida

为深入开展环节动物的分类及遗传进化等研究,比较分析了已登录到GenBank中16种环节动物全基因组的结构特征。结果发现,16种环节动物线粒体全基因组序列中A＋T的含量均超54.3%,碱基G存在低含量的偏向,第三位密码子G含量2.6%-12.7%。基因组的基因组成及排列模式具有一定的保守型,存在5个保守基因联块蔟,线粒体基因组排列顺序在研究环节动物系统发育关系方面起着重要的作用。计算13个编码基因和2个rRNA的基因平均遗传距离,cox1（0.34）相对最保守,atp8（0.8）相对最不保守。大多数环节动物线粒体控制区存在茎环结构。基于13个编码基因氨基酸序列通过3种方法可构建稳健的系统发育树,蛭纲和寡毛纲聚为一进化分枝,构成有环类单系群,螠虫纲、星虫纲和多毛纲聚为一进化分枝,形成单系群。5个纲间的聚类结果与之前的基于线粒体基因和其他分子标记研究研究结果有所不同。多毛纲呈单系发生,被分为两个主要类群,头节动物中的锥头虫科和缩头虫科没有聚为单独的一进化分枝,而是分别聚类到触角动物下面的足刺动物和沟触角动物,多毛纲内部分类不同于现有的形态学分类结果。

In this study,the structure and organization of mitochondrial genomes,a significant tool for understanding of classification and evolutionary history of metazoan animals,were analyzed in 16 species of annelids in GenBank,aiming at further researches of classification and molecular evolution of annelids as an ancient animal phylum.The results showed that there was A＋T content of over 54.3% and low content of G,2.6%—12.7%in their 3rd position,in the mitochondrial genome of 16 species of annelids.The gene order and composition of the mitochondrial genome were conservative,and five conserved gene clusters were found in the mitochondrial genomes playing an important role in phylogeny of annelids.Calculation of average genetic distances of 13protein-coding genes and 2rRNA genes revealed that cox1（0.34）was the most conservative and atp8（0.8）was the least conservative.The stem-loop structure was observed in the putative control region of mitochondrial genomes of most annelids.The robust phylogenetic trees based on amino acid sequences of 13protein-coding genes were constructed by three methods,and the Hirudinea and Oligochaeta formed an volutionary branch which was a monophyletic group Clitellata.Echiura,Sipuncula and Polychaetes also formed a monophyletic group.The evolutionary relationships of 5classes were not consistent with previous researches based on mitochondrial genomes and other molecular data.The class Polychaeta showed monophyletic and had been split into two major groups.The Orbiniidae and Maldanidae which were before classified into the Scolecida did not form an volutionary branch,but were clustered into Aciculata and Canalipalpata,respectively,which were classified into Palpata.Relationships of Polychaeta families were not consistent with the present morphological classification.