Gene Expression Analysis of Cold and Freeze Stress in Baker's Yeast

Abstract

We used mRNA differential display to assess yeast gene expression under cold or freeze shock stress conditions. We found both up-and down-regulation of genes, although repression was more common. We identified and sequenced several cold-induced genes exhibiting the largest differences. We confirmed, by Northern blotting, the specificity of the response for TPI1, which encodes triose-phosphate isomerase; ERG10, the gene for acetoacetyl coenzyme A thiolase; and IMH1, which encodes a protein implicated in protein transport. These genes also were induced under other stress conditions, suggesting that this cold response is mediated by a general stress mechanism. We determined the physiological significance of the cold-induced expression change of these genes in two baker's yeast strains with different sensitivities to freeze stress. The mRNA level of TPI1 and ERG10 genes was higher in freeze-stressed than in control samples of the tolerant strain. In contrast, both genes were repressed in frozen cells of the sensitive strain. Next, we examined the effects of ERG10 overexpression on cold and freeze-thaw tolerance. Growth of wild-type cells at 10°C was not affected by high ERG10 expression. However, YEpERG10 transformant cells exhibited increased freezing tolerance. Consistent with this, cells of an erg10 mutant strain showed a clear phenotype of cold and freeze sensitivity. These results give support to the idea that a cause-and-effect relationship between differentially expressed genes and cryoresistance exists in Saccharomyces cerevisiae and open up the possibility of design strategies to improve the freeze tolerance of baker's yeast.Baker's yeast (Saccharomyces cerevisiae) responds to various stresses during its propagation and industrial application (3, 30). For example, extreme environmental conditions arise during freezing, frozen storage, and thawing of bread dough, resulting in yeast cells with reduced viability and dough-leavening capacity (11,14). These effects have a great technological and economic impact because the yeast gassing rate is critical in baking. Consequently, the improvement of the freeze tolerance in baker's yeast is of significant commercial importance.The response of S. cerevisiae to cold shock stress has not been characterized in detail, but it is generally accepted that freeze-thaw tolerance correlates with cellular factors including growth phase (39), respiratory metabolism (22), lipid composition of the membrane (10), and accumulation of trehalose (23,27,37). Cultural conditions that result in yeast cells with these characteristics, especially high trehalose content, are commonly employed in the production of baker's yeast (3, 30), even though they provide stress resistance only in the absence of fermentable sugars (37). Thus, an additional mechanism(s) is thought to be triggered in response to sharp downshift changes in temperature and to be required for the maintenance of freeze tolerance.Regulatory systems that control the stress response in S. cerevisiae act primarily at the transcr...

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“…Published reports by Rodriguez-Vargas et al and Schade et al provide evidence that alterations in membrane composition at 10°C may be due to changes in global transcriptional patterns (39,40). Although changes in gene expression certainly play a role in altering membrane composition in response to cold, evidence presented in this report suggests that posttranslational regulation is also involved in cold adaptation.…”

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

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