Whole-Genome Duplication and Acceleration of Molecular Evolution are Associated with the Early Diversification of Cornus L. (Cornaceae): Insights from De Novo Assembled Transcriptome Sequences. Cornus

Here we compare ten de novo-assembled transcriptomes representing the major lineages of the angiosperm genus Cornus (dogwood) and relevant outgroups using a customized pipeline for analyses. Using three distinct approaches, molecular dating of orthologous genes, analyses of the distribution of synonymous substitutions between paralogous genes, and examination of substitution rates through time, we detected a shared WGD event in the late Cretaceous across all taxa sampled. The inferred doubling event coincides temporally with the paleoclimatic changes associated with reconstructed increases in sea surface temperature and the initial divergence of the genus into three major lineages. Analyses also showed an immediate acceleration of rates of molecular evolution after WGD. These results, coupled with the information from phylogenetic dating, suggest that the early diversification of Cornus was rapid, and likely driven by WGD and subsequent accelerated molecular evolution associated with environmental stress. The highest rates of molecular evolution were observed in the transcriptome of the herbaceous lineage, C. canadensis, a species commonly found at higher latitudes, including the Arctic.