Small heat-shock protein Hsp12 contributes to yeast tolerance to freezing stress

Abstract

TheHSP12gene encodes one of the two major small heat-shock proteins ofSaccharomyces cerevisiaeand is induced under different conditions, such as low and high temperatures, osmotic or oxidative stress and high sugar or ethanol concentrations. However, few studies could demonstrate any correlation betweenHSP12deletion or overexpression and a phenotype of sensitivity/resistance, making it difficult to attribute a role for Hsp12p under several of these stress conditions. We investigated the possible role of Hsp12p in yeast freezing tolerance. Contrary to what would be expected, thehsp12null mutant when subjected to prolonged storage at −20 °C showed an increased resistance to freezing when compared with the isogenic wild-type strain. Because the mutant strain displayed a higher intracellular trehalose concentration than the wild-type, which could mask the effect of manipulatingHSP12, we overexpressed theHSP12gene in a trehalose-6-phosphate synthase (TPS1) null mutant. Thetps1Δ strain overexpressingHSP12showed an increase in resistance to freezing storage, indicating that Hsp12p plays a role in freezing tolerance in a way that seems to be interchangeable with trehalose. In addition, we show that overexpression ofHSP12in thistps1Δ strain also increased resistance to heat shock and that absence ofHSP12compromises the ability of yeast cells to accumulate high levels of trehalose in response to a mild heat stress.