Ingvarsson Pär K
Umeå Plant Science Centre, Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
Mol Biol Evol. 2007 Mar;24(3):836-44. doi: 10.1093/molbev/msl212. Epub 2007 Jan 4.
Codon bias is generally thought to be determined by a balance between mutation, genetic drift, and natural selection on translational efficiency. However, natural selection on codon usage is considered to be a weak evolutionary force and selection on codon usage is expected to be strongest in species with large effective population sizes. In this paper, I study associations between codon usage, gene expression, and molecular evolution at synonymous and nonsynonymous sites in the long-lived, woody perennial plant Populus tremula (Salicaceae). Using expression data for 558 genes derived from expressed sequence tags (EST) libraries from 19 different tissues and developmental stages, I study how gene expression levels within single tissues as well as across tissues affect codon usage and rates sequence evolution at synonymous and nonsynonymous sites. I show that gene expression have direct effects on both codon usage and the level of selective constraint of proteins in P. tremula, although in different ways. Codon usage genes is primarily determined by how highly expressed a genes is, whereas rates of sequence evolution are primarily determined by how widely expressed genes are. In addition to the effects of gene expression, protein length appear to be an important factor influencing virtually all aspects of molecular evolution in P. tremula.
密码子偏好性通常被认为是由突变、遗传漂变以及对翻译效率的自然选择之间的平衡所决定的。然而，密码子使用上的自然选择被认为是一种较弱的进化力量，并且在有效种群规模较大的物种中，对密码子使用的选择预计最为强烈。在本文中，我研究了长寿木本多年生植物欧洲山杨（杨柳科）同义位点和非同义位点上密码子使用、基因表达与分子进化之间的关联。利用来自19个不同组织和发育阶段的表达序列标签（EST）文库的558个基因的表达数据，我研究了单个组织内以及不同组织间的基因表达水平如何影响同义位点和非同义位点上的密码子使用和序列进化速率。我发现基因表达对欧洲山杨的密码子使用和蛋白质的选择约束水平都有直接影响，尽管方式不同。密码子使用基因主要由基因的高表达程度决定，而序列进化速率主要由基因的广泛表达程度决定。除了基因表达的影响外，蛋白质长度似乎是影响欧洲山杨分子进化几乎所有方面的一个重要因素。
