MBE Advance Access originally published online on September 4, 2008
Molecular Biology and Evolution 2008 25(12):2567-2577; doi:10.1093/molbev/msn194
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Research Articles |
Patterns of Divergence among Conifer ESTs and Polymorphism in Pinus sylvestris Identify Putative Selective Sweeps
* Department of Evolutionary Functional Genomics, Uppsala University, S-752 36 Uppsala, Sweden
Department of Biology, University of Oulu, FIN-90014 Oulu, Finland
Department of Biological Statistics and Computational Biology, Cornell University
E-mail: anna.palme{at}ebc.uu.se.
Accepted for publication August 30, 2008.
Finding genes that are under positive selection is a difficult task, especially in non-model organisms. Here, we have analyzed expressed sequence tag (EST) data from 4 species (Pinus pinaster, Pinus taeda, Picea glauca, and Pseudotsuga menziesii) to investigate selection patterns during their evolution and to identify genes likely to be under positive selection. To confirm selection, population samples of these genes have been sequenced in Pinus sylvestris, a species that was not included in the EST data set. The estimates of branch-specific Ka/Ks (nonsynonymous/synonymous substitution rates) across all genes in the EST data set were similar or smaller than estimates from other higher plant species. There was no evidence for the traditional indication of positive selection, Ka/Ks above 1. However, several lines of evidence based on polymorphism patterns suggest that genes with high Ka/Ks (0.20–0.52) in the EST data set are in fact more affected by positive selection in P. sylvestris than genes with low Ka/Ks (0.01–0.04). The high Ka/Ks genes have a lower level of polymorphism and more negative Tajima's D than the low Ka/Ks genes. Further, in the high Ka/Ks group, the Hudson–Kreitman–Aguade test is significant. This suggests that the EST data set is a good starting point for finding genes under positive selection in conifers and that even moderate Ka/Ks values could be indicative of selection. A group of 5 genes with high Ka/Ks collectively show evidence for positive selection within P. sylvestris.
Key Words: selection • candidate genes • Ka/Ks • dn/ds • Pinus sylvestris • Scots pine
John H McDonald, Associate Editor
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