Identification of causal nucleotide variants within a quantitative trait locus on chromosome 16 for low acetic acid...

Among sake yeasts, Kyokai No. 7 and related strains (the K7 group) are the predominant industrial strains currently used for sake making, being distinguished by their low acetic acid production. Excessive amounts of acetic acid in sake cause an off-flavor known as a vinegar-like odor; thus, reducing its production is desirable. To elucidate the genetic background underlying the low acetic acid production in the K7 group of sake yeast, we conducted quantitative trait locus (QTL) analysis using haploid segregants derived from a hybrid between a haploid derivative of the K7 strain and the laboratory strain. We detected a QTL on chromosome 16 that contributes to low acetic acid production via a sake yeast-type allele. Small-scale sake-making tests were conducted using allele-replaced strains of 14 genes located within the approximately 40 kb QTL interval on chromosome 16, and a gene of unknown function (YPL062W) was identified as a candidate gene. Results from real-time PCR analysis suggested that this gene is unlikely to function as an open reading frame (ORF) but likely functions as part of a promoter region. Additionally, this sequence was found to influence the expression of the gene encoding an aldehyde dehydrogenase, suggesting that its activity might be linked to acetic acid production. Small-scale sake-making tests using K7H-type nucleotide-substitution strains for mutations within this region identified multiple mutations that independently reduced acetic acid production. These results are expected to contribute to the development of DNA marker-assisted breeding for reduced acetic acid production.