池蝶蚌线粒体基因组全序列分析

COMPLETE SEQUENCE ANALYSIS OF MITOCHONDRIAL GENOME IN HYRIOPSIS SCHLEGELII

采用普通PCR扩增、SHOT-GUN测序、软件拼接首次获得了池蝶蚌(Hyriopsis schlegelii)线粒体基因组全序列。线粒体基因组全长为15939 bp,由13个蛋白质编码基因、22个tRNA基因、2个SrRNA基因和28个长度为1—393 bp的非编码区组成;除ND3-ND5、ND4L、ATP6、ATP8、COX1-COX3、tRNA-D、tRNA-H之外,其他大多数基因在L链编码。池蝶蚌线粒体全基因组序列、蛋白编码基因、tRNA基因、rRNA基因及非编码区的A+T含量分别为60.36%、59.84%、61.7%、60.23%及62.5%,与其他淡水蚌类一致,均表现出A+T偏好性,淡水蚌类线粒体基因组长度的差异主要表现在非编码区长度的差异。池蝶蚌mtDNA的COX2-12SrRNA区域基因排列存在差异,是ND3、tRNAHis、tRNAAla、tRNASer1、tRNASer2、tRNAGlu、ND2、tRNAMet 8个基因发生重组造成。22个tRNA基因都具有典型的三叶草二级结构,tRNA-E与tRNA-W间的非编码区含有一个ORF区,而控制区并未发现。从GenBank上下载的14种双壳纲贝类的mtDNA序列构建的系统进化树,显示池蝶蚌与三角帆蚌亲缘关系最近。研究结果为淡水珍珠蚌线粒体基因重排及进化特征提供理论依据。

The complete mitochondrial genome of Hyriopsis schlegelii was obtained by using polymerase chain reaction （PCR）, shot-gun sequencing. The genome contains 15939 base pairs and 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and 28 non-coding regions ranged from 1bp to 393bp in size. Most genes were encoded on the L strand, while ND3-ND5, ND4L, ATP6, ATP8, COX1-COX3, tRNA-D, and tRNA-H were encoded on the H strand. The structure and organization of mitochondrial genomes of H. schlegelii and other 7 freshwater mussels were analyzed by using comparative genomics and bioinformatics methods. Results showed that：（i） Strong bias was toward A＋T for the genome of H. schlegelii. （ii） The striking mitochondrial genome difference in the size performed on the non-coding regions in all the freshwater mussels. （iii） The gene arrangement of H. schlegelii was identical to that of Hyriopsis cumingii and Lamprotula leai, but was different from that of Cristaria plicata, Lampsilis ornate, Pyganodon grandis, Quadrula quadrula and Venustaconcha ellipsiformis between COX2 and 12S rRNA. The difference was caused by rearrangement of 8 genes, including ND3, tRNAHis, tRNAAla, tRNASer1, tRNASer2, tRNAGlu, ND2 and tRNAMet. （iv） Protein-coding genes contained 4 initiation codons which were I （AUU, AUC）, V （GUG）, M （AUG）, and L （UUG） and 13 genes have complete stop codons （UAA or UAG）. （v） 22 tRNAs had typical cloverleaf structure. There were an ORF region between tRNA-E and tRNA-W but no control region. The MP-tree based on mtDNA genomes showed the evolu-tionary position of H. schlegelii relative to that of 14 other bivalvia species. The result showed that H. schlegelii and H. cumingii had the closest relationship than others. The results of this study provide the basis for gene rearrangement and evolutionary characterization of mitochondrial genome in bivalves.