%0 Journal Article
%T Slow but not low: genomic comparisons reveal slower evolutionary rate and higher dN/dS in conifers compared to angiosperms
%A Emmanuel Buschiazzo
%A Carol Ritland
%A J£¿rg Bohlmann
%A Kermit Ritland
%J BMC Evolutionary Biology
%D 2012
%I BioMed Central
%R 10.1186/1471-2148-12-8
%X Based upon pairwise comparisons of 3,723 spruce and pine orthologues, we found an average synonymous genetic distance (dS) of 0.191, and an average dN/dS ratio of 0.314. Using a fossil-established divergence time of 140 million years between spruce and pine, we extrapolated a nucleotide substitution rate of 0.68 ¡Á 10-9 synonymous substitutions per site per year. When compared to angiosperms, this indicates a dramatically slower rate of nucleotide substitution rates in conifers: on average 15-fold. Coincidentally, we found a three-fold higher dN/dS for the spruce-pine lineage compared to the poplar-Arabidopsis lineage. This joint occurrence of a slower evolutionary rate in conifers with higher dN/dS, and possibly positive selection, showcases the uniqueness of conifer genome evolution.Our results are in line with documented reduced nucleotide diversity, conservative genome evolution and low rates of diversification in conifers on the one hand and numerous examples of local adaptation in conifers on the other hand. We propose that reduced levels of nucleotide mutation in large and long-lived conifer trees, coupled with large effective population size, were the main factors leading to slow substitution rates but retention of beneficial mutations.Determining the mutational and the selective forces responsible for evolution has overarching implications in biology, e.g. in understanding what makes species unique and how organisms respond to biotic and abiotic challenges. Identifying the rate of evolution and the patterns of nucleotide substitution underlying DNA evolution has thus become a fundamental goal of molecular genomics [1,2]. Key to the central dogma of molecular biology, protein-coding sequences (hereafter referred to as genes) have classically been regarded as a major unit of evolution. Substitutions at synonymous (silent) and non-synonymous (replacement) sites are commonly distinguished to differentiate between neutral (or at least weak) and active selective f
%U http://www.biomedcentral.com/1471-2148/12/8