Evolution of Repetitive Genomic Content and Gene Families Over Geo-Climatic Gradients in Brassicaceae

On temperature gradients such as elevation or latitude, species turnover is common, and specialists can persist in extreme environments. This is likely paralleled by adaptive and possibly also non-adaptive changes on a molecular level, from genes to the structure of genomes. Here, we investigated associations between elevation and latitude, partly represented by climate variables, with features of the genome, including genome size, transposable element (TE) content, and gene family expansion and contraction in the plant family Brassicaceae. Together, the geo-climatic variables were good predictors of genome size and TE content, explaining 40%-60% of the variation among species. The relationship of TE content with mean annual temperature was U-shaped, with species of cooler and hotter climates generally having more TEs, and those with elevation and mean annual precipitation (both corrected for temperature) were positive. Patterns were most prevalent for the most abundant TE class, long terminal repeat elements (LTR). Gene family expansions and contractions in species of high elevations highlighted a restructured genomic architecture of cell wall modeling, response to temperature stimulus, and processes involved in posttranslational protein modifications. Results point to abiotically extreme environments either promoting high TE content or constraining TE elimination at the level of species. Furthermore, establishing in distinct geo-climatic regions seems associated with considerable parallel evolution with overlapping gene families changing copy numbers.