Abstract
Saccharomyces cerevisiae is used as a host strain in bioproduction, because of its rapid growth, ease of genetic manipulation, and high reducing capacity. However, the heat produced during the fermentation processes inhibits the biological activities and growth of the yeast cells. We performed whole-genome sequencing of 19 intermediate strains previously obtained during adaptation experiments under heat stress; 49 mutations were found in the adaptation steps. Phylogenetic tree revealed at least five events in which these strains had acquired mutations in the CDC25 gene. Reconstructed CDC25 point mutants based on a parental strain had acquired thermotolerance without any growth defects. These mutations led to the downregulation of the cAMP-dependent protein kinase (PKA) signaling pathway, which controls a variety of processes such as cell-cycle progression and stress tolerance. The one-point mutations in CDC25 were involved in the global transcriptional regulation through the cAMP/PKA pathway. Additionally, the mutations enabled efficient ethanol fermentation at 39 °C, suggesting that the one-point mutations in CDC25 may contribute to bioproduction.
Highlights
Saccharomyces cerevisiae is used as a host strain in bioproduction, because of its rapid growth, ease of genetic manipulation, and high reducing capacity
In order to identify mutations that contribute to thermotolerance in S. cerevisiae, we sequenced the whole-genome of the parental strain and 19 intermediate strains isolated in the stepwise breeding[6] (Fig. 1a, DDBJ accession number DRA004175)
Forty-nine genomic mutations including SNPs, insertions, and deletions were identified in the intermediate strains by comparing them with the genomic sequence of MT8-1
Summary
Saccharomyces cerevisiae is used as a host strain in bioproduction, because of its rapid growth, ease of genetic manipulation, and high reducing capacity. Reconstructed CDC25 point mutants based on a parental strain had acquired thermotolerance without any growth defects These mutations led to the downregulation of the cAMP-dependent protein kinase (PKA) signaling pathway, which controls a variety of processes such as cell-cycle progression and stress tolerance. The one-point mutations in CDC25 were involved in the global transcriptional regulation through the cAMP/PKA pathway. Saccharomyces cerevisiae is a widely used host strain for bioproduction, because of its rapid growth under aerobic and anaerobic conditions, ease of genetic manipulation, and high reducing capacity[2]. Despite these advantages, little is known about the mutations involved in thermotolerance. Excessive downregulation of the cAMP/PKA pathway leads to a trade-off between thermotolerance and diminished growth rate, because the cell cycle is under the control of this pathway[15]
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