Nutrient signaling pathways control wine yeast performance

Abstract

Wine yeast adaptation to the industrial conditions is key for its biotechnological success. Saccharomyces cerevisiae has to be able to have a fully respiratory metabolism during biomass production and a strong fermentation power during winemaking and tolerate many different stress conditions. Nutrient signaling pathways control metabolism and stress response depending on the nutrients present and the environmental conditions. Their function is well known in laboratory conditions, but remain quite uncharacterized in industrial processes and in commercial yeasts. Yeast have favorite carbon and nitrogen sources and repress the use of non-preferred ones, via Protein Kinase A/SNF1 and Nitrogen Catabolite Repression (NCR) pathways respectively. Biochemical analysis of the main pathways revealed unexpected behavior during winemaking. For instance, regarding glucose repression mechanisms, Snf1 kinase was activated only when glucose was exhausted under laboratory conditions, but was active from early fermentation stages when sugar levels are very high. Transcription factor Gln3, which activates genes subject to NCR, was also active for the first hours, even when ammonium and amino acids were still present in media. Deletion analysis of regulatory pathways during winemaking also show that GLN3 and SNF1 share a similar impact in fermentation kinetics and metabolite production, suggesting that there are not isolated carbon or nitrogen signaling, but that both are connected. PKA has also a great impact on fermentation, and deletion on cAMP phosphodiesterase PDE2 by CRISPR-Cas9 increase fermentation speed. Stress response proteins have also an impact on metabolism. Peroxiredoxin Tsa1 acts as a redox sensor, and we have found that its deletion impacts defensive carbohydrate trehalose and glycogen accumulation during biomass propagation in molasses. Therefore, nutrient signaling, stress response and metabolism are all well coordinated in yeast to guarantee a successful biotechnological performance.