A role for
aquaporins in yeast freeze tolerance revealed by genome-wide gene expression
analysis.
An Tanghe (1),
Patrick Van Dijck (1), Aloys Teunissen (2), Stefan Hohmann (3), Johan Thevelein
(1)
(1) Lab. of Molecular Cell Biology, Katholieke Universiteit Leuven, Kasteelp.
Arenb. 31, Heverlee, 3001, Belgium (An.Tanghe@bio.kuleuven.ac.be); (2)
Department of Pharmacology, ErasmusMC, Box 1738, 3000 DR-Rotterdam, The
Netherlands; (3) Department of Cell and Molecular Biology, Göteborg University,
Box 462, S-40530 Göteborg, Sweden.
Although much correlative evidence is available, the precise determinants of freeze resistance in Saccharomyces cerevisiae are largely unknown. Genome-wide gene expression analyses of freeze-resistant and -sensitive strains have revealed a correlation between freeze resistance and expression of aquaporin encoding genes. This relationship was confirmed by deletion and overexpression of AQY1 and AQY2, reducing and enhancing yeast freeze tolerance, respectively. Similar effects were obtained in Schizosaccharomyces pombe, Candida albicans and Nicotiana tabacum cells. Heterologous expression of the poorly functional human aquaporin encoding hAQP1-A73M allele supports a role for plasma membrane water transport activity in determination of yeast freeze tolerance. We suggest that rapid osmotically driven water efflux upon freezing reduces intracellular ice crystal formation and resulting cell damage. Aquaporin overexpression also improved maintenance of viability of industrial strains, without affecting commercially important characteristics. These results open new perspectives for the successful development of freeze-resistant baker's yeast strains for frozen dough applications. Unfortunately, the aquaporin-mediated improvement of freeze tolerance seems to be restricted to rapid freezing conditions. Further research is required to evaluate the putative physiological and industrial importance of aquaporin-mediated freeze resistance in yeast and possibly other microorganisms.