Nutritional requirements of wine yeast strains: Role of the TORC1 pathway on winemaking conditions

Trabajo presentado a la 28th International Conference on Yeast Genetics and Molecular Biology (ICYGMB), celebrada en Praga (Republica Checa) del 27 de agosto al 1 de septiembre de 2017.Wine alcoholic fermentation is mainly carried out by enological strains of Saccharomyces cerevisiae, hence the importance of the environmental and genetic factors that determine their growth and aging, not only for their relevance on the fermentative process but also by their impact on wine organoleptic properties. When a nutrient is scarce, dietary restriction happens, which consists in the reduction of nutrients supply without inducing malnutrition. Dietary restriction controls longevity through nutrient signaling pathways, as the TORC1 pathway, which promotes growth and protein synthesis when nitrogen sources are abundant. As sugars are plenty in grape juice, generally is nitrogen the limiting nutrient. Thus, the study of the physiological processes by which a selective nitrogen source is used is of great importance. Hence, our interest in TORC1 targets, such as ribosomal Rps6 protein and the nitrogen catabolic repression (NCR) system, that represses the use of poor nitrogen sources when optimal sources are present. Its main effectors are GATA transcriptional factors (Gln3 and Gat1), controlled mainly by TORC1. The behaviour of NCR transcription factors Gat1 and Gln3 is being studied in wine strains. Our results indicate genetic differences between wine and laboratory yeast strains, mainly in their response to nitrogen shortage. Indeed, using phosphorylation of Rps6 as a tool to study TORC1 activity, our data indicate that wine and laboratory yeast strains behave differently against several TOR inhibitors, such as rapamycin or methionine sulfoximine (MSX). Moreover, TORC1 pathway seems to be only active in the first hours of winemaking, indicating that signalling of nitrogen shortage occurs earlier than expected. Under these conditions, other nutrient signalling pathways (Ras/AMPc/PKA or Snf1) could be active to promote growth, and that aspect is being also addressed. In general, TORC1 pathway can integrate the nitrogen signal and coordinate other pathways to respond to the specific environmental winemaking conditions.Peer reviewe