Complete dominant inheritance of intracellular leucine accumulation traits in polyploid yeasts

The yeast Saccharomyces cerevisiae is widely used for ethanol production. In the production of alcoholic beverages, flavours are affected mainly by yeast metabolism in the fermentation process. To increase the contents of initial scented fruity flavours, such as isoamyl alcohol and isoamyl acetate, leucine accumulation in yeast cells is induced by a decrease of leucine feedback inhibition in the l-leucine synthetic pathway using conventional mutagenesis. Diploid strains are commonly used in sake brewing because of better fermentation performance, such as vitality and endurance, compared with those of haploid strains. Heterozygous mutations are mostly detected in target genes of brewing yeasts generated through mutation breeding. Here we describe that an allele of the LEU4 gene, LEU4(G516S), dominantly induced leucine accumulation even in triploid and tetraploid yeasts as with in diploid yeasts. Importantly, we demonstrated that there is no difference in the intracellular amount of branched-chain amino acids between LEU4(G516S)/LEU4 heterozygous diploids and LEU4(G516S)/LEU4(G516S) homozygous diploids. The approach to increase isoamyl alcohol and isoamyl acetate by intracellular leucine accumulation can potentially be applied to a variety of yeast strains, including aneuploid and polyploid yeasts.

Automated summary

The study found that reducing leucine feedback inhibition in the l-leucine synthetic pathway could induce leucine accumulation in yeast cells, thereby increasing the content of fruity flavors in the fermentation process. A specific allele of the LEU4 gene (LEU4(G516S)) was identified to dominantly induce leucine accumulation in yeast cells, including triploid and tetraploid strains. Furthermore, the intracellular amount of branched-chain amino acids was found to be the same between heterozygous and homozygous diploid strains carrying the LEU4(G516S) allele.