The control of intracellular glycerol in Saccharomyces cerevisiae influences osmotic stress response and resistance to increased temperature

Abstract

Glycerol has been demonstrated to serve as the major osmolyte of Saccharomyces cerevisiae. Consistently, mutant strains gpd1gpd2 and gpp1gpp2, which are devoid of the main glycerol biosynthesis pathway, have been shown to be osmosensitive. In addition, the primary hyperosmotic stress response is affected in these strains. Hog1p phosphorylation turned out to be prolonged and osmostress‐induced gene expression is delayed compared with the kinetics observed in wild‐type cells. A hog1 deletion strain was previously found to contain lower internal glycerol and therefore displays an osmosensitive phenotype. Here, we show that the osmosensitivity of hog1 is suppressed by growth at 37°C. We reasoned that this temperature‐remedial osmoresistance might be caused by a higher intracellular glycerol level at the elevated temperature. This hypothesis was confirmed by measurement of the glycerol concentration, which was shown to be similar for wild type and hog1 cells only at elevated growth temperatures. In agreement with this finding, hog1 cells containing an fps1 allele, encoding a constitutively open glycerol channel, have lost their temperature‐remedial osmoresistance. Furthermore, gpd1gpd2 and gpp1gpp2 strains were found to be temperature sensitive. The growth defect of these strains could be suppressed by adding external glycerol. In conclusion, the ability to control glycerol levels influences proper osmostress‐induced signalling and the cellular potential to grow at elevated temperatures. These data point to an important, as yet unidentified, role of glycerol in cellular functioning.

Thermosensitivity of the Saccharomyces cerevisiae gpp1gpp2 double deletion strain can be reduced by overexpression of genes involved in cell wall maintenance

“…As was shown previously, loss of both genes encoding the glycerol-3-P phosphatases, resulted in an osmosensitive phenotype (Pahlman et al 2001;Siderius et al 2000). This phenotype occurs despite the existence of an alternative metabolic route of glycerol synthesis or the possibility to take it up from the medium through transporters (Blomberg 1997;Lages and Lucas 1997).…”

“…In order to determine the relation between intracellular glycerol level, cell wall adaptations and MAPK pathway activation, we set out to search for multicopy suppressors of the ts phenotype of the gpp1gpp2 double deletion strain (Siderius et al 2000). As expected, the GPP2 gene was isolated a few times.…”

“…Overexpression of GPD1, encoding glycerol-3-phosphate dehydrogenase responsible for the rate-limiting step in glycerol synthesis, suppresses the osmosensitive phenotype. Interestingly, suppression of the osmosensitive phenotype can also be achieved by culturing the cells at elevated temperatures resulting in a higher basal level of glycerol in the cell (Siderius et al 2000). The molecular cause for the higher intracellular glycerol concentration at elevated temperatures could be the increased levels of GPD1 and GPP2 expression.…”

“…Apparently, the alternative means to produce/take up glycerol suYce for the need of glycerol as the precursor of lipids and for the role that glycerol synthesis plays in maintaining cellular redox balance (Ansell et al 1997). However, at elevated temperatures, the gpp1gpp2 strain cannot grow at all, a phenotype that is displayed already by gpp2 single deletion strain (Siderius et al 2000).…”

Identification of a Novel Gene Family Involved in Osmotic Stress Response inCaenorhabditis elegans

“…Mutants in the Hog1 pathway are sensitive to high osmolarity, but this sensitivity is alleviated by growth at high temperature (Siderius et al 2000). The most likely explanation for this alleviation is the activation of a second pathway involving protein kinase C (Pkc1), which responds to high temperature, cell wall damage, and osmotic stress (Gustin et al 1998).…”