MBE Advance Access published online on January 4, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msl212
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Research Article |
Gene Expression and Protein Length Influence Codon Usage and Rates of Sequence Evolution in Populus tremula
Umeå Plant Science Centre Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden, tel: +46-(0)90-786-7414, fax: +46-(0)90-786-6705
e-mail: pelle{at}wallace.emg.umu.se
Accepted for publication December 22, 2006.
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 non-synonymous sites in the long-lived, woody perennial plant Populus tremula (Salicaceae). Using expression data for 558 genes derived from 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 non-synonymous sites. I show that gene expression have direct effects 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.
Key Words: codon bias • gene expression • Populus • translational selection