广西5种常见星虫动物的线粒体基因组特征和系统进化分析

Mitochondrial Genome Characteristics and Phylogenetic Analysis of Five Common Sipunculans (Peanut Worms) in Guangxi

关键词:  北部湾  星虫动物  线粒体基因组  遗传变异  系统进化

Key words:  Beibu Gulf  sipuncula  mitogenome  genetic variation  phylogenetic evolution

摘要:

为探明广西北部湾星虫动物的线粒体基因组遗传变异和基因序列特征，采用高通量测序测定广西北部湾5种常见星虫动物的线粒体基因组，并对其基因序列特征、遗传变异、系统进化进行分析。结果显示，星虫动物线粒体基因组具有典型的无脊椎动物线粒体基因组的特征，基因排列高度保守，特别是其13个蛋白质编码基因（PCGs）。此外，星虫动物线粒体基因组的基因均编码在H链上，并存在3个高度保守的基因排列区块，与环节动物和螠虫动物线粒体基因组特征较为相似。cox1、cox2和cob等3个基因进化速率最慢、遗传变异水平最低，适合作为星虫动物种属系统进化研究以及不同种间生物条形码构建的分子标记。nad6、nad4、nad5和nad2等4个基因的遗传变异水平较高（大于60%），变异位点数量较多，适合作为星虫动物种群遗传多样性研究的分子标记。星虫动物线粒体13个蛋白质编码基因的Ka/Ks比值均低于1（0.058 2-0.726 6），其中cox1、cox3和cob等3个基因的Ka/Ks比值最低（小于0.1），表明在星虫动物线粒体遗传进化过程中，这3个蛋白质编码基因承受强烈的自然选择压力和功能束缚。基于线粒体基因组蛋白质编码基因系统进化树的研究结果表明，星虫动物可分为方格星虫纲和革囊星虫纲两个进化分支，星虫动物与环节动物的进化地位、亲缘关系较近，而与软体动物的亲缘关系较远。本研究结果不仅为广西北部湾特色星虫动物渔业资源多样性调查和保护提供分子遗传数据，也为星虫动物系统进化研究提供了科学参考。

Abstract:

In order to ascertain the genetic variation and gene sequence characteristics of the mitochondrial genomes of sipunculans in Guangxi Beibu Gulf,the high-throughput sequencing technique was used to determine the mitochondrial genomes of 5 common sipunculans in the Beibu Gulf of Guangxi.And their gene sequence characteristics,genetic variation and system evolution were analyzed.The results show that the mitochondrial genome of sipunculans has the characteristics of a typical invertebrate mitochondrial genome,and the gene arrangement is highly conservative,especially its 13 protein-coding genes (PCGs). In addition,the genes of the mitochondrial genome of sipunculans are all encoded on the H chain,and there are three highly conserved gene arrangement blocks,which are similar to the mitochondrial genome characteristics of Annelida and Echiura mitogenome.Among sipunculans,the three genes,cox1,cox2 and cob,have the slowest evolution rate and the lowest level of genetic variation.They are suitable to be used as molecular markers for the study of the systematic evolution of sipunculans and the construction of bio-barcodes for identification species. nad6,nad4,nad5,nad2 genes have a relatively high genetic variation level (greater than 60%),and a large number of mutation sites which are suitable to be used as a molecular markers for the study of the genetic diversity of sipunculans populations.The Ka/Ks ratios of the 13 PCGs in the sipunculans were all lower than 1 (0.058 2-0.726 6),and the Ka/Ks ratio of three genes,cox1,cox3, and cob, was the lowest (less than 0.1),indicating that during the genetic evolution of insect mitochondria,these three protein-coding genes are under strong natural selection pressure and functional constraints.The research results based on the phylogenetic tree of mitochondrial genome protein-coding genes show that sipunculans can be divided into two evolutionary branches,the Sipunculidea and the Phascolosomatidea.The evolutionary status and genetic relationship of the sipunculans and annelids are close,and the kinship with mollusks is far away.This study not only provides molecular genetic data for the investigation and protection of the diversity of sipunculans fishery resources in the Beibu Gulf,but also provides a scientific basis for the systematic evolution study of sipunculans.