Abstract
Saccharomyces uvarum is one of the few fermentative species that can be used in winemaking, but its weak sulfite tolerance is the main reason for its further use. Previous studies have shown that the expression of the methionine synthase gene (MET4) is upregulated in FZF1 (a gene encoding a putative zinc finger protein, which is a positive regulator of the transcription of the cytosolic sulfotransferase gene SSU1) overexpression transformant strains, but its exact function is unknown. To gain insight into the function of the MET4 gene, in this study, a MET4 overexpression vector was constructed and transformed into S. uvarum strain A9. The MET4 transformants showed a 20 mM increase in sulfite tolerance compared to the starting strain. Ninety-two differential genes were found in the transcriptome of A9-MET4 compared to the A9 strain, of which 90 were upregulated, and two were downregulated. The results of RT-qPCR analyses confirmed that the expression of the HOMoserine requiring gene (HOM3) in the sulfate assimilation pathway and some fermentation-stress-related genes were upregulated in the transformants. The overexpression of the MET4 gene resulted in a significant increase in sulfite tolerance, the upregulation of fermentation-stress-related gene expression, and significant changes in the transcriptome profile of the S. uvarum strain.
Highlights
The quality of wine depends, to a certain extent, on the species or strain of yeast used in the fermentation process [1]
Three of the larger transformants grown in sulfite-tolerant medium were picked for RT-qPCR analysis, which showed that their relative expression was 10.11-fold higher than the mean value of the starting strain, with the difference reaching significance (p-value < 0.01)
Comparison with transformants transfected with the SSU1 gene and the FZF1 gene indicates that the transfection of this gene can enhance sulfite tolerance in grape juice yeast, but to a lesser extent than the overexpression transformants of the two genes mentioned above (See Table 2) [8,9]
Summary
The quality of wine depends, to a certain extent, on the species or strain of yeast used in the fermentation process [1]. In addition to the common brewing yeasts, Saccharomyces uvarum is often used in winemaking because of its ability to ferment at low temperatures and its ability to produce specific aromas [2]. Sulfites are known to be a widely used preservative that is toxic to many microorganisms, and can give wines a specific flavor during fermentation in the presence of yeast [3]. There are no compounds that can completely replace this additive because of its multifunctional properties, for example, the inhibition of the growth and enzymatic activity of the other microorganisms during winemaking and preservation [3,4]. Sulfite resistance in winemaking yeast is considered to be a vital trait in winemaking
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