Specific gene regulations of non-usual micronutrient starvations leading to cell death during wine fermentation

Yeast cell death can occur during wine alcoholic fermentation, leading to stuck fermentations, which are a major issue for winemakers. Cell death is generally considered to result from ethanol stress that negatively affects membrane integrity. However, it has been recently found that yeast cell death is also related to nitrogen metabolism. Indeed, nitrogen starvation is one of the most frequently encountered starvations in oenological conditions, and yeast is correspondingly able to cope with these deficiencies. However, cell death can also result from yeast inability to implement an appropriate stress response under some conditions of nutrient limitations, most likely not encountered by yeast in the wild. More specifically, a set of micronutrients (oleic acid, ergosterol, pantothenic acid and nicotinic acid) was identified that led to cell death when present in low, growth-restricting concentrations. After an examination of gene expression under conditions of imbalance between nitrogen and these non-traditional micronutrients, it appeared that, in addition to already identified mechanisms of gene regulation in relation to nitrogen metabolism, some genes had specific deficiency regulations that may also explain some of the observed cell mortality. Our data include specific regulations of certain key genes of lipid metabolism as well as others concerning DNA stability under unusual deficiency conditions. Our work allows us to propose a model of the mechanisms involved in controlling yeast mortality under oenological fermentation conditions.