Abstract
SummaryThe toxic effect of ethanol is one of the most important handicaps for many biotechnological applications of yeasts, such as bioethanol production. Elucidation of ethanol stress response will help to improve yeast performance in biotechnological processes. In the yeast Saccharomyces cerevisiae, ethanol stress has been recently described as an activator of the unfolded protein response (UPR), a conserved intracellular signalling pathway that regulates the transcription of ER homoeostasis‐related genes. However, the signal and activation mechanism has not yet been unravelled. Here, we studied UPR's activation after ethanol stress and observed the upregulation of the key target genes, like INO1, involved in lipid metabolism. We found that inositol content influenced UPR activation after ethanol stress and we observed significant changes in lipid composition, which correlate with a major membrane fluidity alteration by this amphipathic molecule. Then, we explored the hypothesis that membrane fluidity changes cause UPR activation upon ethanol stress by studying UPR response against fluidification or rigidification agents and by studying a mutant, erg2, with altered membrane fluidity. The results suggest that the membrane fluidification effects of ethanol and other agents are the signal for UPR activation, a mechanism that has been proposed in higher eukaryotes.
Highlights
Yeasts are key organisms involved in a myriad of biotechnological applications, such as the production of alcoholic drinks or fuels as bioethanol
To gain insights into the mechanism that activates unfolded protein response (UPR) in response to ethanol stress, we focused on the key target genes that have been previously characterized for their activation through this pathway after ER stress
We studied the mRNA levels of a gene involved in inositol metabolism, INO1, and four genes involved in protein folding, ERO1, LHS1, HLJ1 and MPD1, after exposing cells to physiological levels of ethanol (8%)
Summary
Yeasts are key organisms involved in a myriad of biotechnological applications, such as the production of alcoholic drinks or fuels as bioethanol. Ethanol is a small two-carbon alcohol which, given its short alkene chain and the hydroxyl group, is soluble in both aqueous and lipid environments and can pass to cells through the plasmatic membrane by producing an increase in membrane fluidity (Jones and Greenfield, 1987; Lloyd et al, 1993). This fluidity increase causes loss of membrane integrity and favours permeability (Marza et al, 2002). This effect has been described in ethanol-resistant bacteria (Kinji, 1974; Ingram, 1990), while accumulation of other lipids, such as ergosterol, has been related to ethanol resistance due to an increased stability of membranes (Shobayashi et al, 2005; Aguilera et al, 2006)
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