Glycerol accumulation in the dimorphic yeast Saccharomycopsis fibuligera: cloning of two glycerol 3‐phosphate dehydrogenase genes, one of which is markedly induced by osmotic stress

Abstract

Glycerol plays an important role in the osmoadaptation responses of Saccharomyces cerevisiae. However, there is no detailed investigation about the role of glycerol in the osmoadaptation responses of Saccharomycopsis fibuligera. Here we show that both intra- and extracellular glycerol concentrations in Sm. fibuligera cells responded very quickly when they were subjected to osmotic stress. We then cloned two isogenes encoding putative NAD(+)-dependent glycerol 3-phosphate dehydrogenase (GPD) from Sm. fibuligera PD70 by degenerate PCR and subsequent chromosome walking methods. Those two genes, designated SfGPD1 and SfGPD2, respectively, exhibited 86.6% pairwise identity in their encoding regions, while there was no obvious homology in their non-coding regions. Either SfGPD1 or SfGPD2 could complement the salt tolerance characteristics of the gpd1gpd2 double mutant strain of S. cerevisiae, further demonstrating that both of those genes are functional homologues of S. cerevisiae GPD1 and GPD2. Northern blot analysis revealed that SfGPD1 was induced markedly by osmotic stress, while SfGPD2 was not. In consistency with the observation that there was no obvious glycerol content change when the cells were transferred to anoxic conditions, neither SfGPD1 nor SfGPD2 was induced when the cells were transferred to anoxic conditions, thus suggesting a functional splitting of glycerol 3-phosphate dehydrogenase between S. cerevisiae and Sm. fibuligera.