Mu Xidong, Yang Yexin, Liu Yi, Luo Du, Xu Meng, Wei Hui, Gu Dangen, Song Hongmei, Hu Yinchang
Key Laboratory of Tropical&Subtropical Fishery Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Xingyu Road1, Guangzhou, 510380, China.
Parasit Vectors. 2017 Jan 6;10(1):11. doi: 10.1186/s13071-016-1956-9.
Mitochondrial (mt) genome sequences are widely used for species identification and to study the phylogenetic relationships among Gastropoda. However, to date, limited data are available as taxon sampling is narrow. In this study we sequenced the complete mt genomes of the freshwater gastropods Radix swinhoei (Lymnaeidae) and Planorbarius corneus (Planorbidae). Based on these sequences, we investigated the gene rearrangement in these two species and the relationships with respect to the ancestral gene order and assessed their phylogenetic relationships.
The complete mt genomes of R. swinhoei and P. corneus were sequenced using Illumina-based paired-end sequencing and annotated by comparing the sequence information with that of related gastropod species. Putative models of mitochondrial gene rearrangements were predicted for both R. swinhoei and P. corneus, using Reishia clavigera mtDNA structure as the ancestral gene order. The phylogenetic relationships were inferred using thirteen protein sequences based on Maximum likelihood and Bayesian inference analyses.
The complete circular mt genome sequences of R. swinhoei and P. corneus were 14,241 bp and 13,687 bp in length, respectively. Comparison of the gene order demonstrated complex rearrangement events in Gastropoda, both for tRNA genes and protein-coding genes. The phylogenetic analyses showed that the family Lymnaeidae was more closely related to the family Planorbidae, consistent with previous classification. Nevertheless, due to the position recovered for R. swinhoei, the family Lymnaeidae was not monophyletic.
This study provides the complete mt genomes of two freshwater snails, which will aid the development of useful molecular markers for epidemiological, ecological and phylogenetic studies. Additionally, the predicted models for mt gene rearrangement might provide novel insights into mt genome evolution in gastropods.
线粒体（mt）基因组序列被广泛用于物种鉴定以及研究腹足纲动物之间的系统发育关系。然而，迄今为止，由于分类群抽样范围狭窄，可用数据有限。在本研究中，我们对淡水腹足类动物斯氏萝卜螺（椎实螺科）和角圆扁螺（扁卷螺科）的完整线粒体基因组进行了测序。基于这些序列，我们研究了这两个物种中的基因重排情况以及与祖先基因顺序的关系，并评估了它们的系统发育关系。
采用基于Illumina的双末端测序法对斯氏萝卜螺和角圆扁螺的完整线粒体基因组进行测序，并通过将序列信息与相关腹足类物种的序列信息进行比较来进行注释。以枝背螺线粒体DNA结构作为祖先基因顺序，预测了斯氏萝卜螺和角圆扁螺线粒体基因重排的可能模型。基于最大似然法和贝叶斯推断分析，利用13个蛋白质序列推断系统发育关系。
斯氏萝卜螺和角圆扁螺的完整环状线粒体基因组序列长度分别为14241 bp和13687 bp。基因顺序比较表明，腹足纲动物中无论是tRNA基因还是蛋白质编码基因都发生了复杂的重排事件。系统发育分析表明，椎实螺科与扁卷螺科的关系更为密切，这与之前的分类一致。然而，由于斯氏萝卜螺的位置，椎实螺科并非单系类群。
本研究提供了两种淡水螺的完整线粒体基因组，这将有助于开发用于流行病学、生态学和系统发育研究的有用分子标记。此外，预测的线粒体基因重排模型可能为腹足纲动物线粒体基因组进化提供新的见解。
