Enhancement of volatile thiol release of Saccharomyces cerevisiae strains using molecular breeding

Abstract

Cysteine-conjugated volatile thiols are powerful aromatic compounds that contribute to the fruity notes of many white wines and especially Sauvignon Blanc. Genetic selection programs of wine yeast starters able to produce more volatile thiols constitute, therefore, an important goal for the wine industry. Recent investigations on yeast metabolism suggested that the ß-lyase Irc7p and the control of its gene expression by nitrogen catabolite repression constitute a rational way for yeast genetic improvement. This work demonstrates that the use of a natural ure2 mutation can be used to design wine starters with an enhanced capacity of volatile thiols production. By applying backcrosses driven by molecular markers, this allelic form was introduced in different starter backgrounds. Our investigations demonstrate that the ure2 inheritance is able to enhance the production of 4MMP (recently renamed 4MSP) and 3MH (recently renamed 3SH). For 4MMP, this effect depends of the presence of the allele IRC7LT encoding a long form of the Irc7 protein. Moreover, a correlation in between the expression level of this allelic form and 4MMP production was found within industrial starters. All together, these results emphasised the use of molecular breeding for improving quantitative traits of industrial strains without the use of genetically modifying strategies.

Unravelling glutathione conjugate catabolism in Saccharomyces cerevisiae: the role of glutathione/dipeptide transporters and vacuolar function in the release of volatile sulfur compounds 3-mercaptohexan-1-ol and 4-mercapto-4-methylpentan-2-one

“…Specific and relatively uncommon alleles of IRC7 have been shown to determine 4-MMP release from its cysteine precursor (Dufour et al 2013;Roncoroni et al 2011), while 3-MH release remains ambiguous, with other genes such as STR3 potentially involved (Holt et al 2011). Recent evidence suggests that other metabolic pathways may also contribute to 3-MH formation during fermentation .…”

Inactivating Mutations in Irc7p Are Common in Wine Yeasts, Attenuating Carbon-Sulfur β-Lyase Activity and Volatile Sulfur Compound Production

“…Interestingly, while Irc7p was found to be the key determinant of 4-MMP release from Cys-4-MMP and is a significant contributor to 3-MH release from Cys-3-MH (27), most strains of S. cerevisiae have a 38-bp deletion in the IRC7 coding sequence that renders the protein inactive (27,30). It has been hypothesized that the presence or absence of this deletion might account for the strain variation observed in 4-MMP release, and a positive correlation between the expression level of the full-length and active version of IRC7 and 4-MMP production within industrial strains has been reported (31). Irc7p also shows cysteine desulfhydrase activity, thereby releasing ammonium and H 2 S (32), and this deletion has the potential to affect formation of negative VSCs during winemaking.…”

A study of phenotypic plasticity ofSaccharomyces cerevisiaein natural grape juices shed light on allelic variation under balanced selection

“…Therefore, in order to match enological practices as closely as possible, the genetic material used was derived from commercial wine starters and the culture conditions used were natural grape juices. This choice was also motivated by the possibility of using the QTLs detected in further selection programs using molecular markers as previously described (Marullo et al 2007; Dufour et al 2013; Noble, Sanchez, et Blondin 2015).…”