A Genome based approach to characterize genes involved in yeast adaptation to Sherry-like wines’ biological ageing

Wine fermentation and flor ageing are performed by two different lineages of yeast strains, with very different lifestyles. In this thesis we have studied the genome of flor yeast in comparison to wine yeast in order to unravel their specificities. We have first developed a set of haploid flor strains for the molecular evaluation of different targets, and developed as well a synthetic media mimicking wine for that purpose. From the genome sequence of 16 strains (8 wine and 8 flor) from France, Hungary, Italy and Spain we have drawn a phylogeny that showed that flor yeast represent a specific group of yeast different from wine and identified divergent regions. These regions contain genes involved in key functions and several associated with velum growth. Remarkably, many genes involved inFLO11regulation such as MAP kinase, or Ras/PKA pathways were mutated among flor strains and many variations were encountered in genes involved with metal homeostasis such as zinc and divalent metal transporters. The impact of allelic variation of several genes has been evaluated for: the phosphatidylinositol 4-kinasePIK1possibly involved in pseudohyphal growth, the high affinity zinc transporterZRT1, and of the major pyruvate decarboxylasePDC1in order to assess their role in the flor phenotype.