Patterns of Divergence among Conifer ESTs and Polymorphism in Pinus sylvestris Identify Putative Selective Sweeps

• Finding genes that are under positive selection is a difficult task, especially in non-model organisms. Here, we haveanalyzed expressed sequence tag (EST) data from 4 species (Pinus pinaster, Pinus taeda, Picea glauca, and Pseudotsugamenziesii) to investigate selection patterns during their evolution and to identify genes likely to be under positiveselection. To confirm selection, population samples of these genes have been sequenced in Pinus sylvestris, a species thatwas not included in the EST data set. The estimates of branch-specific Ka/Ks (nonsynonymous/synonymous substitutionrates) across all genes in the EST data set were similar or smaller than estimates from other higher plant species. Therewas no evidence for the traditional indication of positive selection, Ka/Ks above 1. However, several lines of evidencebased on polymorphism patterns suggest that genes with high Ka/Ks (0.20–0.52) in the EST data set are in fact moreaffected by positive selection in P. sylvestris than genes with low Ka/Ks (0.01–0.04). The high Ka/Ks genes have a lowerlevel of polymorphism and more negative Tajima’s D than the low Ka/Ks genes. Further, in the high Ka/Ks group, theHudson–Kreitman–Aguade test is significant. This suggests that the EST data set is a good starting point for findinggenes under positive selection in conifers and that even moderate Ka/Ks values could be indicative of selection. A groupof 5 genes with high Ka/Ks collectively show evidence for positive selection within P. sylvestris.

Ämnesord

NATURVETENSKAP  -- Biologi -- Genetik (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Genetics (hsv//eng)

Nyckelord

selection

candidate genes

Ka/Ks

dn/ds

Pinus sylvestris

Scots pine

Genetics

Genetik

Genetics

genetik

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