Interspecific hybridization and aneuploidy as adaptive mechanisms in saccharomyces yeasts

Resumen

With the explosion of genome sequencing technologies, mechanisms such as aneuploidy, polyploidy, and hybridization are emerging as being more frequent and relevant than what was considered earlier. An interesting model to study such mechanisms is Saccharomyces yeast as much data is available on its genome structure and evolution, and important hybrids between the different species of the genus are known. In this doctoral thesis, we aimed to investigate different aspects of the adaptive value of aneuploidy and interspecific hybridization in Saccharomyces. In the first chapter, we were interested in studying what genomic differences were underlying the different ethanol tolerance observed in S. cerevisiae strains. The most interesting genomic change we observed was a shared polysomy of chromosome III in the highest ethanol tolerant strains. We could determine that this correlation between ethanol tolerance and chromome III copy number also appeared in different background and we confirmed it was an adaptive mechanism on ethanol stress. In the second chapter of this work, we asked how S. cerevisiae x S. kudriavzevii hybrids mate and how this mechanism would influence the genomic and adaptability outcome of these hybrids. We found that rare-mating was the most frequent but not the only mechanism used and that the ploidy outcome influenced the phenotype of the strain. In chaper 3, we studied in detail the genome of the hybrid VIN7 and showed that its genome was unstable. The instability influenced the stress resistance of the strain suggesting that genomic instability, probably triggered by hybridization, is an important factor of phenotypic variability, and therefore to adaptability. The fouth chapter of this work deals with short-term evolution of artificial hybrids between S. cerevisiae and S. kudriavzevii. We wanted to know how the genome content changed in conditions in which the species that form the hybrid had different phenotype : ethanol, were S. cerevisiae is better fit, and cold temperature, where the best species is S. kudriavzevii. We showed that recombination between subgenome was less frequent than between the two copies of the S. cerevisiae subgenome. We found that ploidy was strongly influencing transcription and the evolution mechanisms available for the hybrids. We determined also that the selection on transcriptional rewiring during the evolution occurred at processes levels instead of genes or subgenomes.