Absence of Gup1p in Saccharomyces cerevisiae results in defective cell wall composition, assembly, stability and morphology

Saccharomyces cerevisiae Gup1p and its homologue Gup2p, members of the superfamily of membrane-bound O-acyl transferases, were previously associated with glycerol-mediated salt-stress recovery and glycerol symporter activity. Several other phenotypes suggested Gup1p involvement in processes connected with cell structure organization and biogenesis. The gup1Δ mutant is also thermosensitive and exhibits an altered plasma membrane lipid composition. The present work shows that the thermosensitivity is independent of glycerol production and retention. Furthermore, the mutant grows poorly on salt, ethanol and weak carboxylic acids, suggestive of a malfunctioning membrane potential. Additionally, gup1Δ is sensitive to cell wall-perturbing agents, such as Calcofluor white, Zymolyase, lyticase and sodium dodecyl sulphate and exhibits a sedimentation/aggregation phenotype. Quantitative analysis of cell wall components yielded increased contents of chitin and β-1,3-glucans and lower amounts of mannoproteins. Consistently, scanning electron microscopy showed a strikingly rough surface morphology of the mutant cells. These results suggest that the gup1Δ is affected in cell wall assembly and stability, although the Slt2p/MAP kinase from the PKC pathway was phosphorylated during hypo-osmotic shock to a normal extent. Results emphasize the pleiotropic nature of gup1Δ, and are consistent with a role of Gulp1p in connection with several pathways for cell maintenance and construction/remodelling.