线粒体基因组在红血南极鱼和白血南极鱼中的适应性进化

Adaptive Evolution of Mitochondrial Genome in Red-blooded Antarctic Fish and White-blooded Antarctic Fish

线粒体有着自身独有的线粒体基因组并且编码氧化磷酸化相关的13个蛋白。通过氧化磷酸化反应,线粒体可以产生大量的三磷酸腺苷(adenosine triphosphate,ATP)和活性氧以满足生物日常活动中对能量的需求。血红蛋白的丢失使得白血南极鱼运输氧气的能力大幅下降,其线粒体基因组中的蛋白编码基因会在选择压力的作用下产生适应性的进化以补偿氧气供给的不足。为了分析血红蛋白对南极鱼线粒体基因组进化的影响,本文选取了三类鱼进行分析:6种白血南极鱼,5种红血南极鱼,以及与它们亲缘关系较近的9种热带地区鱼类作为实验对象,来探究这三类鱼线粒体蛋白编码基因在进化上的差异,包括进化速率分析、放松性选择分析、多态性氨基酸位点检测以及3D结构预测分析。研究结果表明,红血南极鱼线粒体基因组的进化速率远高于白血南极鱼和热带鱼,并且只有红血南极鱼的线粒体蛋白编码基因受到了放松性的选择压力作用。此外,多态性氨基酸位点检测表明红血南极鱼线粒体基因组编码的氨基酸序列中,多态性位点数量远远高于白血南极鱼和热带鱼;进一步证明红血南极鱼受到了放松性的选择作用。与此相对的是,白血南极鱼的线粒体蛋白编码基因进化速率较低,大部分基因受到强化性选择作用,蛋白质序列中的多态性位点也较少。本研究表明,血红蛋白在南极鱼中的存在与否可能影响线粒体基因组的适应性进化。

Mitochondron has its own unique mitochondrial genome which encodes 13 proteins related to oxidative phosphorylation.Through the oxidatire phosphorylation,the mitochondron can produce a large amount of adenosine triphosphate(ATP)and reactive oxygen species to meet the energy requirements of biological daily activities.The loss of hemoglobin in white-blooded Antarctic fish results in drastically decreased oxygen carrying capacity.Therefore,these mitochondrial protein-coding genes may be under adaptive evolution to cope with the oxygen supply challenge.To investigate the impact of hemoglobin on the evolution of the Antarctic fish mitochondrial protein-coding genes,we analyzed three kinds of fishes,including 6 white-blooded Antarctic fishes,5 redblooded Antarctic fishes,and 9 tropical fishes.we estimated evolutionary rates,relaxed selections,the polymorphisms of homologous sites and 3D structure prediction of 13 protein encoding genes.We found that evolutionary rates of mitochondrial genome were relatively increased in red-blooded Antarctic fishes than that of white-blood Antarctic fishes and tropical fishes.Furthermore,these genes were only under relaxed selection in red-blooded Antarctic fish.More amino acid polymorphic sites were presented in red-blooded Antarctic fish than the other two groups.On the contrary,the evolutionary rates of these genes in the white-blooded Antarctic fishes were relatively decreased and some genes were under intensified selection;the polymorphic sites of amino acid sequences were relatively less than that of red-blooded Antarctic fishes.This study indicates that existence of hemoglobin could affect the evolutionary behavior of the mitochondrial genes in Antarctic fishes.