Genetic Basis for Osmosensitivity and Genetic Instability of the Wine YeastSaccharomyces cerevisiaeVIN7

Saccharomyces cerevisiae is exposed to sugar-induced osmotic stress in fermenting grape must. As part of the osmotic stress response, yeast strains display different phenotypes for acetic acid and glycerol formation in wine. We investigated why an osmosensitive industrial wine yeast, VIN7, produces high amounts of acetic acid and glycerol compared with the industrial wine yeast ST. Comparison of global gene expression patterns revealed that Hog1p and Msn2/Msn4p-regulated genes are expressed at higher levels in VIN7. Furthermore, data suggests that acetic acid production by wine yeast is the result of the reaction catalyzed by Ald6p and influenced by the pentose phosphate pathway and lipid biosynthesis. PCR analyses on the genome of VIN7 revealed that ~30 Kb on the left arm of chromosome XV, close to the telomere, is absent. Among the genes absent is YOL159C, a gene whose deletion causes osmosensitivity and an increase in Ty1 retrotranspositions, which may cause genetic instability in S. cerevisiae.