Stl1 transporter mediating the uptake of glycerol is not a weak point of Saccharomyces kudriavzevii's low osmotolerance.

Saccharomyces kudriavzevii is a nonconventional and rather osmosensitive yeast with a high potential of use in fermentation processes. To elucidate the basis of its relative osmosensitivity, the role of the STL1 gene encoding a putative glycerol uptake system was studied. Under higher osmotic pressure, the addition of a low amount of glycerol to the growth medium improved the growth of S. kudriavzevii and the expression of the STL1 gene was highly induced. Deletion of this gene decreased the strain's ability to grow in the presence of higher concentrations of salts and other solutes. Moreover, the mutant had a disturbed homeostasis of intracellular pH. Expression of the SkSTL1 gene in Saccharomyces cerevisiae complemented the osmosensitivity of the S. cerevisiae hog1Δ stl1Δ mutant, and the gene's tagging with GFP localized its product to the plasma membrane. Altogether, a deficiency in glycerol uptake did not seem to be the reason for S. kudriavzevii's low osmotolerance; its Stl1 transporter properly contributes to the regulation of intracellular pH and is crucial to its survival of osmotic stress. SIGNIFICANCE AND IMPACT OF THE STUDY: An increasing demand for food products with benefits for human health turns the attention to less-exploited nonconventional yeasts with interesting traits not found in Saccharomyces cerevisiae. Among them, Saccharomyces kudriavzevii has good potential for aroma-compound production, fermentations and other biotechnological applications, but it is less adapted to stressful industrial conditions. This report studied S. kudriavzevii relative osmosensitivity and its capacity for active glycerol uptake. The results obtained (on the activity and physiological function of S. kudriavzevii glycerol transporter) may contribute to a further engineering of this species aiming to improve its osmotolerance.

The human protein kinase HIPK2 phosphorylates and downregulates the methyl-binding transcription factor ZBTB4.

HIPK2 is a eukaryotic Serine-Threonine kinase that controls cellular proliferation and survival in response to exogenous signals. Here, we show that the human transcription factor ZBTB4 is a new target of HIPK2. The two proteins interact in vitro, colocalize and associate in vivo, and HIPK2 phosphorylates several conserved residues of ZBTB4. Overexpressing HIPK2 causes the degradation of ZBTB4, whereas overexpressing a kinase-deficient mutant of HIPK2 has no effect. The chemical activation of HIPK2 also decreases the amount of ZBTB4 in cells. Conversely, the inhibition of HIPK2 by drugs or by RNA interference causes a large increase in ZBTB4 levels. This negative regulation of ZBTB4 by HIPK2 occurs under normal conditions of cell growth. In addition, the degradation is increased by DNA damage. These findings have two consequences. First, we have recently shown that ZBTB4 inhibits the transcription of p21. Therefore, the activation of p21 by HIPK2 is two-pronged: stimulation of the activator p53, and simultaneous repression of the inhibitor ZBTB4. Second, ZBTB4 is also known to bind methylated DNA and repress methylated sequences. Consequently, our findings raise the possibility that HIPK2 might influence the epigenetic regulation of gene expression at loci that remain to be identified.

Wine yeast strains engineered for glycogen overproduction display enhanced viability under glucose deprivation conditions.

We used metabolic engineering to produce wine yeasts with enhanced resistance to glucose deprivation conditions. Glycogen metabolism was genetically modified to overproduce glycogen by increasing the glycogen synthase activity and eliminating glycogen phosphorylase activity. All of the modified strains had a higher glycogen content at the stationary phase, but accumulation was still regulated during growth. Strains lacking GPH1, which encodes glycogen phosphorylase, are unable to mobilize glycogen. Enhanced viability under glucose deprivation conditions occurs when glycogen accumulates in the strain that overexpresses GSY2, which encodes glycogen synthase and maintains normal glycogen phosphorylase activity. This enhanced viability is observed under laboratory growth conditions and under vinification conditions in synthetic and natural musts. Wines obtained from this modified strain and from the parental wild-type strain don't differ significantly in the analyzed enological parameters. The engineered strain might better resist some stages of nutrient depletion during industrial use.