银色裂腹鱼线粒体基因组序列特征与系统进化分析

Mitochondrial genome sequence characteristics and phylogenetic analysis of Schizothorax argentatus

摘要:

银色裂腹鱼（Schizothorax argentatus）在我国仅分布于新疆地区的伊犁河流域，是我国裂腹鱼类中珍稀濒危品种之一，具有较高的科研和经济价值。本研究采用高通量测序技术获得了银色裂腹鱼长度为16 580 bp的线粒体基因组全序列，其基因组成和排列顺序均与典型的脊椎动物相似，共有13个蛋白质编码基因、22个tRNA基因、2个rRNA基因和1个非编码区（D-loop）。碱基组成分别为A （30.25%）、G （17.28%）、C （27.20%）和T （25.27%），呈现明显的AT偏好性和反G偏倚。tRNA基因中仅tRNA-Ser^（GCU）因缺少二氢尿嘧啶茎而无法形成典型的三叶草结构。ND6基因的AT-skew和GC-skew值波动最大，揭示该基因经历的选择和突变压力可能与其他基因不同。银色裂腹鱼线粒体控制区包含了3个不同的结构域：终止序列区（ETAS）、中央保守区（CSB-F、CSB-E、CSB-D和CSB-B）和保守序列区（CSB1、CSB2和CSB3），且在CSB3下游约50 bp处识别到鲤形目（Cypriniformes）鱼类中普遍存在的保守序列片段TT （AT） nGTG。基于28种裂腹鱼属鱼类线粒体基因组全序列构建的系统发育关系表明银色裂腹鱼分化时间较早，与其他类群亲缘关系较远，这可能与其所生活的水域地理位置和水文环境有密切关系。

Abstract:

Schizothorax argentatus that only distributes in the Ili River basin in Xinjiang is one of the rare and endangered species of schizothorax in China, thus has high scientific and economic values. In this study, the complete mitochondrial genome sequence of S. argenteus with a length of 16 580 bp was obtained by high-throughput sequencing. The gene compositions and arrangement were similar to those of typical vertebrates. It contained 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a non-coding region (D-loop). The nucleotide compositions were A (30.25%), G (17.28%), C (27.20%), and T (25.27%), respectively, showing obvious AT bias and anti-G bias. Among the tRNA genes, only tRNA-Ser^(GCU) could not form a typical cloverleaf structure due to the lack of dihydrouracil arm. The AT-skew and GC-skew values of the ND6 gene were fluctuating the most, suggesting that the gene may experience different selection and mutation pressures from other genes. The mitochondrial control region of S. argenteus contained three different domains, i.e., termination sequence region (ETAS), central conserved region (CSB-F, CSB-E, CSB-D, and CSB-B), and conserved sequence region (CSB1, CSB2, and CSB3). The conserved sequence fragment TT (AT) nGTG, which was ubiquitous in Cypriniformes, was identified at about 50 bp downstream CSB3. Phylogenetic relationships based on the complete mitochondrial genome sequence of 28 Schizothorax species showed that S. argenteus had differentiated earlier and had a distant relationship with other species, which may be closely related to the geographical location and the hydrological environment where it lives.