GC content evolution in coding regions of angiosperm genomes: a unifying hypothesis

• We propose a new hypothesis to explain gene GC-content patterns in plants.
• Recombination gradients along genes could explain GC-content gradients.
• Gene gradients and gene structures could drive GC-content distributions.
• Methylation and nucleosome positioning could also have a role.

In angiosperms (as in other species), GC content varies along and between genes, within a genome, and between genomes of different species, but the reason for this distribution is still an open question. Grass genomes are particularly intriguing because they exhibit a strong bimodal distribution of genic GC content and a sharp 5′–3′ decreasing GC content gradient along most genes. Here, we propose a unifying model to explain the main patterns of GC content variation at the gene and genome scale. We argue that GC content patterns could be mainly determined by the interactions between gene structure, recombination patterns, and GC-biased gene conversion. Recent studies on fine-scale recombination maps in angiosperms support this hypothesis and previous results also fit this model. We propose that our model could be used as a null hypothesis to search for additional forces that affect GC content in angiosperms.