Transcriptomic shift in ethanol and amino acid metabolic genes regulated by Med15 during fermentation

Wine yeast are specialized strains that are adapted to survive in the wine making environment while producing high concentrations of ethanol. In addition to large genomic changes that differentiate wine yeast from yeast used in other industries, single nucleotide and polyglutamine tract polymorphisms in the transcriptional regulator Med15 are associated with the fermentation efficiency and stress response phenotypes of wine yeast. In this study we investigated the transcriptional differences during wine fermentation in transgenic lab strain yeast having integrated wine yeast MED15 alleles. Compared to the lab strain, a strain with a MED15 allele from a palm wine yeast strain, exhibited enhanced expression of glycolytic, fermentation, and amino acid biosynthesis genes. Our experimental data confirms the importance of arginine biosynthetic genes during the fermentation process and suggests that the improvement in fermentation efficiency in strains with MED15 alleles from wine yeast strains may be related to the role of Med15 in expression of the genes of the arginine biosynthetic pathway. The global benefit conferred by polymorphisms in a single transcriptional regulator, makes Med15 a prime target for engineering of strains devoted to various types of alcohol production. Individual fermentation reactions in 5 mL supplemented white grape juice were prepared for two biological replicates each of the med15Δ strain and integrants of the LAB, WY7, WY15, and WY23 MED15 alleles. Weight loss was monitored, and RNA was extracted from yeast at the 35% weight loss point (~37 hours for MED15 strains, and 48 hours for med15Δ strains).