Conditional Osmotic Stress in Yeast

Abstract

The accumulation and transport of solutes are hallmarks of osmoadaptation. In this study we have employed the inability of the Saccharomyces cerevisiae gpd1⌬ gpd2⌬ mutant both to produce glycerol and to adapt to high osmolarity to study solute transport through aquaglyceroporins and the control of osmostress-induced signaling. High levels of different polyols, including glycerol, inhibited growth of the gpd1⌬ gpd2⌬ mutant. This growth inhibition was suppressed by expression of the hyperactive allele Fps1-⌬1 of the osmogated yeast aquaglyceroporin, Fps1. The degree of suppression correlated with the relative rate of transport of the different polyols tested. Transport studies in secretory vesicles confirmed that Fps1-⌬1 transports polyols at increased rates compared with wild type Fps1. Importantly, wild type Fps1 and Fps1-⌬1 showed similarly low permeability for water. The growth defect on polyols in the gpd1⌬ gpd2⌬ mutant was also suppressed by expression of a heterologous aquaglyceroporin, rat AQP9. We surmised that this suppression was due to polyol influx, causing the cells to passively adapt to the stress. Indeed, when aquaglyceroporin-expressing gpd1⌬ gpd2⌬ mutants were treated with glycerol, xylitol, or sorbitol, the osmosensing HOG pathway was activated, and the period of activation correlated with the apparent rate of polyol uptake. This observation supports the notion that deactivation of the HOG pathway is closely coupled to osmotic adaptation. Taken together, our "conditional" osmotic stress system facilitates studies on aquaglyceroporin function and reveals features of the osmosensing and signaling system.

Pheromone-Induced Morphogenesis Improves Osmoadaptation Capacity by Activating the HOG MAPK Pathway

“…We compared reporter expression in cells grown in the presence of 1 M sorbitol or with 0.5 M sorbitol and 0.5 M glycerol. These two media present a similar osmotic challenge (30). However, in the second solution yeast experience a lower glycerol gradient and expression of the HOG reporter was lower than in 1 M sorbitol, adopting a value intermediate between 1 M glycerol and 1 M sorbitol (Fig.…”

Yeast responses to stresses associated with industrial brewery handling: Figure 1

“…The HOG pathway also appears to regulate the activity of the glyceroaquaporin Fps1p (Luyten et al, 1994;Tamás et al, 1999;Karlgren et al, 2005), which reduces the net efflux of glycerol and thus aids intracellular accumulation. The HOG pathway also appears to regulate the activity of the glyceroaquaporin Fps1p (Luyten et al, 1994;Tamás et al, 1999;Karlgren et al, 2005), which reduces the net efflux of glycerol and thus aids intracellular accumulation.…”

Factors Influencing the Production of Sensory Active Substances in Brewer's and Wine Yeast

“…HOG dráha pravděpodobně reguluje i membránový protein Fsp1 ovlivňující tok glycerolu. Mutanti S. cerevisiae, kterým protein Fsp1 chyběl, byli citliví na osmotický šok (Karlgren et al, 2005).…”

“…HOG pathway probably regulates the membrane protein Fsp1 that affects the fl ow of glycerol. Mutants of S. cerevisiae lacking Fsp1 protein were sensitive to osmotic shock (Karlgren et al, 2005).…”