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 by comparative genomics using the plant family
Brassicaceae. Together, the geo-climatic variables were good predictors of
TE content and genome size, explaining 40-60% or more of the variation
among species. The relationship between mean annual temperature and TE
content was U-shaped, with species of cooler and hotter climates generally
having more TEs. The relationships 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 regarding cell
wall modeling, the response to temperature stimulus and processes involved
in posttranslational protein modifications. Results point to abiotically
extreme environments either favoring high TE contents or constraining TE
silencing on the level of species. Furthermore, establishing in distinct
geo-climatic regions seems associated with considerable parallel evolution
with overlapping gene families changing copy numbers.