Existence of a tightly regulated water channel in Saccharomyces cerevisiae

Meyrial, Valerie; Laizé, Vincent; Gobin, Renée; Ripoche, Pierre; Hohmann, Stefan; Tacnet, Frédérique

doi:10.1046/j.1432-1327.2001.01882.x

Cited by 17 publications

(34 citation statements)

References 26 publications

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“…Aquaporins mediate the rapid transport of water across the plasma membrane (2,26). Our hypothesis is that higher levels of aquaporins in the plasma membrane allow rapid water efflux, especially at freezing temperatures, when water diffusion through the phospholipid layer of the membrane is limiting.…”

Section: Discussionmentioning

confidence: 99%

Aquaporin-Mediated Improvement of Freeze Tolerance of Saccharomyces cerevisiae Is Restricted to Rapid Freezing Conditions

Tanghe

Dijck

Colavizza

et al. 2004

Appl Environ Microbiol

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Previous observations that aquaporin overexpression increases the freeze tolerance of baker's yeast (Saccharomyces cerevisiae) without negatively affecting the growth or fermentation characteristics held promise for the development of commercial baker's yeast strains used in frozen dough applications. In this study we found that overexpression of the aquaporin-encoding genes AQY1-1 and AQY2-1 improves the freeze tolerance of industrial strain AT25, but only in small doughs under laboratory conditions and not in large doughs under industrial conditions. We found that the difference in the freezing rate is apparently responsible for the difference in the results. We tested six different cooling rates and found that at high cooling rates aquaporin overexpression significantly improved the survival of yeast cells, while at low cooling rates there was no significant effect. Differences in the cultivation conditions and in the thawing rate did not influence the freeze tolerance under the conditions tested. Survival after freezing is determined mainly by two factors, cellular dehydration and intracellular ice crystal formation, which depend in an inverse manner on the cooling velocity. In accordance with this so-called two-factor hypothesis of freezing injury, we suggest that water permeability is limiting, and therefore that aquaporin function is advantageous, only under rapid freezing conditions. If this hypothesis is correct, then aquaporin overexpression is not expected to affect the leavening capacity of yeast cells in large, industrial frozen doughs, which do not freeze rapidly. Our results imply that aquaporinoverexpressing strains have less potential for use in frozen doughs than originally thought.Although much correlative evidence is available, the determinants of freeze resistance in Saccharomyces cerevisiae are largely unknown (for a review see reference 34). The injury sustained during freezing and thawing is caused by a combination of multiple types of stress imposed on the cells, such as changes in temperature, water content, water state, pH, and free radical, ion, and solute concentrations. The concomitant loss of survival is not attributable to any one form of injury and depends on the cooling and warming rates, the final temperature, the duration of freezing, and the suspending medium (23,24).When a cell suspension is cooled to a temperature of 0°C or less, both the suspending medium and the cells initially supercool. Extracellular ice crystal formation precedes intracellular freezing and is determined by the freezing point of the suspending medium and the presence of ice-nucleating agents. Based only on osmolarity, the freezing point of the cytoplasm is predicted to be approximately Ϫ1°C. Nevertheless, the cell interior typically remains unfrozen until the temperature is Ϫ10 to Ϫ15°C. This intracellular supercooling may be due to prevention of growth of ice into the cell interior by the cell membrane and due to the lack of nucleators of supercooled water within the cell (23, 24).Following external fr...

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Section: Discussionmentioning

confidence: 99%

Aquaporin-Mediated Improvement of Freeze Tolerance of Saccharomyces cerevisiae Is Restricted to Rapid Freezing Conditions

Tanghe

Dijck

Colavizza

et al. 2004

Appl Environ Microbiol

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“…However, the somewhat unusual strain ⌺1278b, which is also used to study pseudohyphal development, appears to have functional AQY1 and AQY2 genes (82,311). While the water transport function of Aqy1p has been demonstrated in the heterologous oocyte system, water transport via Aqy2p could not be shown in that system (54,82,382).…”

Section: Mip Channelsmentioning

confidence: 99%

Osmotic Stress Signaling and Osmoadaptation in Yeasts

Hohmann

2002

Microbiol Mol Biol Rev

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1,440

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The ability to adapt to altered availability of free water is a fundamental property of living cells. The principles underlying osmoadaptation are well conserved. The yeast Saccharomyces cerevisiae is an excellent model system with which to study the molecular biology and physiology of osmoadaptation. Upon a shift to high osmolarity, yeast cells rapidly stimulate a mitogen-activated protein (MAP) kinase cascade, the high-osmolarity glycerol (HOG) pathway, which orchestrates part of the transcriptional response. The dynamic operation of the HOG pathway has been well studied, and similar osmosensing pathways exist in other eukaryotes. Protein kinase A, which seems to mediate a response to diverse stress conditions, is also involved in the transcriptional response program. Expression changes after a shift to high osmolarity aim at adjusting metabolism and the production of cellular protectants. Accumulation of the osmolyte glycerol, which is also controlled by altering transmembrane glycerol transport, is of central importance. Upon a shift from high to low osmolarity, yeast cells stimulate a different MAP kinase cascade, the cell integrity pathway. The transcriptional program upon hypo-osmotic shock seems to aim at adjusting cell surface properties. Rapid export of glycerol is an important event in adaptation to low osmolarity. Osmoadaptation, adjustment of cell surface properties, and the control of cell morphogenesis, growth, and proliferation are highly coordinated processes. The Skn7p response regulator may be involved in coordinating these events. An integrated understanding of osmoadaptation requires not only knowledge of the function of many uncharacterized genes but also further insight into the time line of events, their interdependence, their dynamics, and their spatial organization as well as the importance of subtle effects

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“…The physiological role of aquaporins in yeasts is still being debated and remains unclear (3,7). The discovery that aquaporins enhance cellular tolerance for rapid freezing in Saccharomyces cerevisiae suggests their ecological and physiological relevance, which is reinforced by their observed conservation during evolution, since aquaporin genes have been found in 67% of the 33 species of eukaryotic microbes whose genomes have been sequenced (7).…”

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confidence: 99%