Abstract
The production of acetic acid during wine fermentation is a critical issue for wineries since the sensory quality of a wine can be affected by the amount of acetic acid it contains. We found that the C2H2-type zinc-finger transcription factor YML081Wp regulated the mRNA levels of ALD4 and ALD6, which encode a cytosolic acetaldehyde dehydrogenase (ACDH) and a mitochondrial ACDH, respectively. These enzymes produce acetate from acetaldehyde as part of the pyruvate dehydrogenase bypass. This regulation was also reflected in the protein levels of Ald4p and Ald6p, as well as total ACDH activity. In the absence of ALD6, YML081W had no effect on acetic acid levels, suggesting that this transcription factor’s effects are mediated primarily through this gene. lacZ reporter assays revealed that Yml081wp stimulates ALD6 transcription, in large part from a GAGGGG element 590 base pairs upstream of the translation start site. The non-annotated ORF YML081W therefore encodes a transcription factor that regulates acetate production in Saccharomyces cerevisiae. We propose AAF1 as a gene name for the YML081W ORF.
Highlights
During fermentation, yeast cells are exposed to a challenging environment: low pH, hypoxia, high osmotic pressure, and a rising ethanol concentration
This paper shows that Yml081wp stimulates expression of both the ALD4 and ALD6 genes, and that the regulation of ALD6 in particular is the basis of its acetic acid phenotype
Strain Construction All strains used in this paper were based on the industrial M2 wine yeast [8,9]. This strain of Saccharomyces cerevisiae was chosen for its amenability to genetic manipulation, as well as its ability to carry out industrial wine fermentations
Summary
Yeast cells are exposed to a challenging environment: low pH, hypoxia, high osmotic pressure, and a rising ethanol concentration. 62 of these genes are non-annotated; they are not linked to any specific function. We have been exploring wine fermentation as a means for elucidating a role for these genes in yeast metabolism. We created wine yeast strains that carry null mutations for each of the 62 non-annotated FSR genes. We created strains that overexpress each non-annotated FSR gene. These strains were used to perform wine fermentations. We observed that the null strain for one FSR gene, YML081W, produced less acetic acid than its wild-type counterpart. The strain overexpressing YML081W produced wine with elevated acetic acid levels. We investigated the role and mechanism of Yml081Wp in regulating acetic acid production
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