Data from: Patterns and evolution of nucleotide landscapes in seed plants

Nucleotide landscapes, which is the way base composition is distributed
along a genome, strongly vary among species. The underlying causes of
these variations have been much debated. Though mutational bias and
selection were initially invoked, GC-biased gene conversion (gBGC), a
recombination-associated process favoring the G and C over A and T bases,
is increasingly recognized as a major factor. As opposed to vertebrates,
evolution of GC content is less well known in plants. Most studies have
focused on the GC-poor and homogeneous Arabidopsis genome and the much
more GC-rich and heterogeneous rice (Oryza sativa) genome and has often
been generalized as a dicot/monocot dichotomy. This vision is clearly
phylogenetically biased and does not allow understanding the mechanisms
involved in GC-content evolution in plants. To tackle these issues, we
used EST data from more than 200 species and provided the most
comprehensive description of gene GC content across the seed plant
phylogeny so far available. As opposed to the classically assumed
dicot/monocot dichotomy, we found continuous variations in GC content from
the probably ancestral GC-poor and homogeneous genomes to the more derived
GC-rich and highly heterogeneous ones, with several independent enrichment
episodes. Our results suggest that gBGC could play a significant role in
the evolution of GC content in plant genomes.