Weak acid and alkali stress regulate phosphatidylinositol bisphosphate synthesis in Saccharomyces cerevisiae

摘要

pWeak organic acids are used as food preservatives to inhibit the growth of spoilage yeasts, including iSaccharomyces cerevisiae/i. Long-term adaptation to weak acids requires the increased expression of the ATP-binding cassette transporter Pdr12p, which catalyses the active efflux of the weak acids from the cytosol; however, very little is known about the signalling events immediately following application of weak acid stress. We have investigated the effects of weak acids on two stress-responsive signalling molecules, PtdIns(3,5)iP/isub2/sub and PtdIns(4,5)iP/isub2/sub, which in iS. cerevisiae/i are synthesized by Fab1p and Mss4p respectively. At low extracellular pH, benzoic acid, sorbic acid and acetic acid all cause a transient reduction in PtdIns(3,5)iP/isub2/sub accumulation and a more persistent rise in PtdIns(4,5)iP/isub2/sub levels. The increase in PtdIns(4,5)iP/isub2/sub levels is accompanied by a reorganization of the actin cytoskeleton. However, changes in PtdInsiP/isub2/sub levels are independent of weak acid-induced Pdr12p expression. In contrast, changing the extracellular medium to alkaline pH provokes a prolonged and substantial rise in PtdIns(3,5)iP/isub2/sub levels. As PtdIns(3,5)iP/isub2/sub synthesis is required for correct vacuole acidification, it is possible that levels of this molecule are modulated to maintain intracellular pH homoeostasis in response to weak acid and alkali stresses. In conclusion, we have expanded the repertoire of stress responses that affect PtdInsiP/isub2/sub levels to include weak acid and alkali stresses./p