Mutation exposed: a neutral explanation for extreme base composition of an endosymbiont genome.
Mutation exposed: a neutral explanation for extreme base composition of an endosymbiont genome.
复制标题
突变暴露：内共生体基因组极端碱基组成的中性解释。
DOI：
10.1007/s00239-003-0192-z
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发表时间：
2004
影响因子：
3.9
通讯作者：
Funk,DanielJ
中科院分区：
文献类型：
--
作者：
Wernegreen,JenniferJ;Funk,DanielJ
中性突变压力与选择对碱基组成进化的影响是一个相当有争议的问题。然而，目前的研究代表了第一个明确的人口遗传学分析，这个问题在原核生物中，其中碱基组成的变化是最显着的。在这里，我们探讨的影响，突变和选择的同义词变化的动态inBuchnera aphidicola，富AT的细菌内共生体的蚜虫。具体而言，我们评估了三种形式的证据。(i)我们比较了Buchner种内和种间同义位点的定向碱基变化（AT→GC vs. GC→AT）的频率，以测试这些突变类别的选择性偏好与有效中性。在一个强大的种内同源性重建的突变变化显示出近1：1的AT→GC：GC→AT的比例。同样地，碱基组成的稳定性表明布氏种的AT→GC和GC→AT取代率相等。物种内部和物种之间的这些模式的相似性支持中性模型。(ii)我们观察到一个等效的相对每个站点AT突变率和当前AT含量在同义站点，表明碱基组成是在突变平衡。(iii)我们在记录同义位点选择的平行哺乳动物研究中证明了Buchnerathan突变类别频率在统计学上更大的平等性。我们的研究结果表明，有效的中性突变压力，而不是选择，是主要的驱动力在Buchnera基地组成的演变。因此，他们进一步证实了最近的证据reducedNe在细菌内共生体的分子进化中的关键作用。
The influence of neutral mutation pressure versus selection on base composition evolution is a subject of considerable controversy. Yet the present study represents the first explicit population genetic analysis of this issue in prokaryotes, the group in which base composition variation is most dramatic. Here, we explore the impact of mutation and selection on the dynamics of synonymous changes inBuchnera aphidicola, the AT-rich bacterial endosymbiont of aphids. Specifically, we evaluated three forms of evidence. (i) We compared the frequencies of directional base changes (AT→GC vs. GC→AT) at synonymous sites within and betweenBuchneraspecies, to test for selective preference versus effective neutrality of these mutational categories. Reconstructed mutational changes across a robust intraspecific phylogeny showed a nearly 1:1 AT→GC:GC→AT ratio. Likewise, stationarity of base composition amongBuchneraspecies indicated equal rates of AT→GC and GC→AT substitutions. The similarity of these patterns within and between species supported the neutral model. (ii) We observed an equivalence of relative per-site AT mutation rate and current AT content at synonymous sites, indicating that base composition is at mutational equilibrium. (iii) We demonstrated statistically greater equality in the frequency of mutational categories inBuchnerathan in parallel mammalian studies that documented selection on synonymous sites. Our results indicate that effectively neutral mutational pressure, rather than selection, represents the major force driving base composition evolution inBuchnera. Thus they further corroborate recent evidence for the critical role of reducedNein the molecular evolution of bacterial endosymbionts.