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Gene Expression during Model Dough Fermentation after Freezing Preservation of S. cerevisiae Baker’s Yeast Cells

ABSTRACT: Freeze-thaw stress causes various cellular damages, survival and proliferation defects, and metabolic alterations, although how cells cope with it is poorly understood. In this study, model dough fermentations using two different strains of Saccharomyces cerevisiae baker’s yeast were compared after two-week cell preservation in the refrigerator or in the freezer. As a result, one strain specifically exhibited a decreased fermentation rate after exposed to freeze-thaw stress. A DNA microarray analysis of the cells during fermentation revealed that the genes involved in oxidative phosphorylation were upregulated after the freeze-thawing process in the stress-sensitive strain, suggesting a metabolism switching from glycolysis to respiration. In the identical strain, however, most of the genes that encode the components of the proteasome complex were commonly downregulated, and ubiquitinated proteins were highly accumulated by freeze-thaw stress. In the cells with a laboratory-strain background, treatment with a proteasome inhibitor MG132 or deletion of each transcriptional activator gene for the proteasomal genes (RPN4, PDR1, or PDR3) led to a marked decrease in the rate of model dough fermentation using the frozen cells. Based on these data, degradation of freeze-thaw damaged proteins by proteasome may guarantee the high fermentation performance. Furthermore, a heterozygous dominant-negative PDR3 allele (A148T/A229V/H336R/L541P) was found in the diploid genome of the stress-sensitive baker’s yeast strain, which may be associated with the decreased fermentation rate. Removal of such responsible mutations may improve the freeze-thaw stress tolerance and the fermentation performance of baker’s yeast strains, as well as other industrial S. cerevisiae yeast strains.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE101071 | GEO | 2017/07/11

SECONDARY ACCESSION(S): PRJNA393668

REPOSITORIES: GEO

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Project description:Saccharomyces cerevisiae is exposed to freeze-thaw stress in commercial processes including frozen dough baking. The cell viability and fermentation activity after freeze-thaw were dramatically decreased due to freeze-thaw injury. Because freeze-thaw injury involves complex phenomena, the mechanisms of it are not fully understood. We attempted to analyze the mechanisms of freeze-thaw injury by indirect gene expression analysis during post-thaw incubation after freeze-thaw treatment using DNA microarray profiling. The results showed that a high frequency of the genes involved in the homeostasis of metal ions were up-regulated depending on the freezing period. The phenotype of the deletion mutants of the up-regulated genes extracted by indirect gene expression analysis was assessed. The deletion strains of the MAC1 and CTR1 genes involved in copper ion homeostasis exhibited freeze-thaw sensitivity, suggesting that copper ion homeostasis is required for freeze-thaw tolerance. Supplementation with copper ions during post-thaw incubation increased intracellular superoxide dismutase activity. Inverse correlated with intracellular superoxide dismutase activity, intracellular levels of reactive oxygen species were decreased. Moreover, cell viability increased by supplementation with copper ions under specific assessment conditions. This study suggested that insufficiency of copper ion homeostasis may be one of the causes of freeze-thaw injury. Total RNA was extracted from the stress-treated yeast cells by using a hot phenol method. Poly(A)+ RNA was enriched from total RNA by using an Oligotex dT30 (Super) mRNA purification kit (Takara Bio, Ohtsu, Japan). cDNA synthesis, cRNA synthesis, and labeling were performed according to the Affymetrix user’s manual (Affymetrix, Santa Clara, USA). Biotinyated cRNA was fragmented and then used as a probe.Affimetrix Yeast Genome 2.0 arrays (Affymetrix) were used as DNA microarrays. All experiments were done in triplicate independently.

Project description:In frozen dough baking technology, bakerâs yeast Saccharomyces cerevisiae encounter freeze-thaw injury. After thawing, dramatically decrease in cell viability and fermentation activity is caused by freeze-thaw injury. The freezing period is critical factor in freeze-thaw injury, thus we focused and investigated time-dependent gene expression profiles in recovery process from freeze injury. First, changes in gene expression profiles in S. cerevisiae in recovery process from freeze-thaw injury were analyzed using a DNA microarray. The results showed the genes which were involved in homeostasis of metal ions were time-dependent up-regulated 2-fold or more in a series. Then we examined whether these genes were related to tolerance in freeze-thaw injury by using deletion strain. The results showed that deletion of MAC1, CTR1, and PCA1 genes which involved in copper ion transport exhibited freeze-thaw sensitivity in compared with wild type. These genes are involved in copper ion uptake to a cell under a copper deficiency condition or in copper ion homeostasis, suggesting that it may be related between freeze-thaw injury and copper ion transport. To determine the effect of supplementation of copper ion on cells after freeze-thaw treatment, cell viability, intracellular superoxide dismutase (SOD) activity, and intracellular levels of reactive oxygen species (ROS) were examined by various copper ion condition medium. The results showed that intracellular SOD activity was increased and intracellular levels of ROS were decreased by supplementation of copper ion, but there was no significant difference in cell viability. These results of the present study may suggest that copper ion concentration in yeast cell after freeze-thaw treatment is important to recovery from freeze-thaw injury due to redox control of intracellular levels of ROS, but copper ion did not directly affect cell viability. Experiment Overall Design: Total RNA was extracted from the stress-treated yeast cells by using a hot phenol method. Poly(A)+ RNA was enriched from total RNA by using an Oligotex dT30 (Super) mRNA purification kit (Takara Bio, Ohtsu, Japan). cDNA synthesis, cRNA synthesis, and labeling were performed according to the Affymetrix userâs manual (Affymetrix, Santa Clara, USA). Biotinyated cRNA was fragmented and then used as a probe.Affimetrix Yeast Genome 2.0 arrays (Affymetrix) were used as DNA microarrays. All experiments were done in duplicate independently

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Gene Expression during Model Dough Fermentation after Freezing Preservation of S. cerevisiae Baker’s Yeast Cells

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