Abstract
BackgroundThiamine availability is involved in glycolytic flux and fermentation efficiency. A deficiency of this vitamin may be responsible for sluggish fermentations in wine making. Therefore, both thiamine uptake and de novo synthesis could have key roles in fermentation processes. Thiamine biosynthesis is regulated in response to thiamine availability and is coordinated by the thiamine sensor Thi3p, which activates Pdc2p and Thi2p. We used a genetic approach to identify quantitative trait loci (QTLs) in wine yeast and we discovered that a set of thiamine genes displayed expression-QTL on a common locus, which contains the thiamine regulator THI3.ResultsWe deciphered here the source of these regulatory variations of the THI and PDC genes. We showed that alteration of THI3 results in reduced expression of the genes involved in thiamine biosynthesis (THI11/12/13 and THI74) and increased expression of the pyruvate decarboxylase gene PDC1. Functional analysis of the allelic effect of THI3 confirmed the control of the THI and PDC1 genes. We observed, however, only a small effect of the THI3 on fermentation kinetics. We demonstrated that the expression levels of several THI genes are correlated with fermentation rate, suggesting that decarboxylation activity could drive gene expression through a modulation of thiamine content. Our data also reveals a new role of Thi3p in the regulation of the main pyruvate decarboxylase gene, PDC1.ConclusionsThis highlights a switch from PDC1 to PDC5 gene expression during thiamine deficiency, which may improve the thiamine affinity or conservation during the enzymatic reaction. In addition, we observed that the lab allele of THI3 and of the thiamin transporter THI7 have diverged from the original alleles, consistent with an adaptation of lab strains to rich media containing an excess of thiamine.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-1085) contains supplementary material, which is available to authorized users.
Highlights
Thiamine availability is involved in glycolytic flux and fermentation efficiency
Mapping of expression quantitative trait locus (QTL) over THI3 location Our previous study concerning the genetic analysis of expression variations during wine fermentation, in synthetic must [16] revealed a hotspot of 11 eQTLs that mapped to the position 310 kbp on chromosome 4
Several of these genes are involved in thiamine metabolism including thiamine biosynthesis (THI5/11/12/13) and thiamine mitochondrial transport (THI74), or regulated by thiamine level and have a putative role in thiamine metabolism (PET18) [18]
Summary
Thiamine availability is involved in glycolytic flux and fermentation efficiency. A deficiency of this vitamin may be responsible for sluggish fermentations in wine making. The glycolytic-fermentation pathway is an essential metabolic process that is linked to the availability of enzyme cofactors, such as NADH/NADPH [1] or vitamins, especially thiamine pyrophosphate (TPP). This vitamin is involved in pyruvate decarboxylation to acetaldehyde. The addition of thiamine to musts is a common practice in many cellars Yeasts actively incorporate this vitamin at the beginning of wine fermentation and no thiamine is left in the medium after six hours [4]. While PDC1 expression is reportedly not controlled by thiamine level, PDC5 expression is activated during thiamine deficiency by an unknown mechanism [9]
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