The role of large-scale gene duplication in the evolution of the eukaryotic membrane traffic system

While the role of gene duplication in the evolution of individual proteins or interacting protein pairs has been well documented, less is known about the conditions under which large gene sets are duplicated. The membrane traffic system of eukaryotic cells dynamically emerges via the interaction of proteins belonging to large gene families, such as Rabs, SNAREs, and coats. Biophysical and phylogenetic analyses suggest that the evolution of organelles with new compositions requires gene family expansion. Both whole-genome duplication and inter-species hybridization are sources of such genetic novelty. What is the fate of gene duplicates arising from these distinct processes? The lager brewing yeast Saccharomyces pastorianus is an ideal model system to study this question. This allotetraploid species arose about 500 years ago via a hybridization event, closely followed by a whole-genome duplication event. We have compared the hybrid with its parents, using genome, transcriptome and functional assays. Our data show that hybridization outstrips whole-genome duplication as a source of persistent genetic novelty. Hybridization may have thus played a pivotal role in the evolution of unicellular eukaryotes.