Exploring genome plasticity and adaptive evolution in natural and de novo laboratory hybrid yeast species.
Barbara Dunn (1), Giani Liti (2), Ed Louis (2), R. Frank Rosenzweig (3), Gavin Sherlock (1)
(1) Department of Genetics, Stanford University, Stanford, CA 94305-5120, USA; (2) Department of Genetics, University of Leicester, University Road, Leicester LE1 7RH United Kingdom; (3) Division of Biological Sciences, The University of Montana, 32 Campus Drive #4824, Missoula MT, USA
Genome rearrangements have been implicated as a driving mechanism in the speciation of many organisms, as well as in the progression of cancers and various human aneuploidy syndromes. Using microarray-based Comparative Genomic Hybridization (array-CGH), in conjunction with novel two-species oligonucleotide microarrays, we have tracked, on a whole-genome scale, the chromosomal rearrangements that occur in both the S. cerevisiae and S. bayanus genomes during the initial steps of de novo speciation in laboratory-made hybrid yeasts formed between these two species. Furthermore, we have carried out the same analyses on S. pastorianus strains, which are natural hybrids of S. cerevisiae and S. bayanus. In the de novo laboratory hybrids, we have found that extensive whole-chromosome aneuploidy, sometimes involving more than half of the S. cerevisiae chromosomes, is the major type of chromosomal change seen during the early stages of hybrid speciation. In the S. pastorianus strains, we have identified several different rearrangements that occur in different isolates. While many of the rearrangements are found in multiple isolates, none of the isolates are identical; each distinct set of rearrangements thus defines a fingerprint for a particular strain. In the future, we will monitor genome rearrangements that occur in these newly-formed species during adaptive evolution as they are grown for many generations in chemostats under various stress conditions, and determine whether many of the rearrangements seen in S. pastorianus are recapitulated in the laboratory-generated species under the appropriate selective pressure(s). These studies represent not only the first genome-wide assessment of the extent and types of genome rearrangements that have occurred in extant natural hybrid species, but also rearrangements that occur during real-time hybrid speciation.