Characterization of alcohol-induced filamentous growth in Saccharomyces cerevisiae

Diploid cells of the budding yeast Saccharomyces cerevisiae starved for nit rogen differentiate into a filamentous growth form. Poor carbon sources suc h as starches can also stimulate filamentation, whereas haploid cells under go a similar invasive growth response in rich medium. Previous work has dem onstrated a role for various alcohols, by-products of amino acid metabolism , in altering cellular morphology. We found that several alcohols, notably isoamyl alcohol and 1-butanol, stimulate filamentous growth in haploid cell s in which this differentiation is normally repressed. Butanol also induces cell elongation and changes in budding pattern, leading to a pseudohyphal morphology, even in liquid medium. The filamentous colony morphology and ce ll elongation require elements of the pheromone-responsive MAPK cascade and TEC1, whereas components of the nutrient-sensing machinery, such as MEP2 G PA2, and GPR1, do not affect this phenomenon. A screen for 1-butanol-insens itive mutants identified additional proteins that regulate polarized growth (BUD8, BEM1, BEM4, and FIG1), mitochondrial function (MSM1, MRP21, and HMI 1), and a transcriptional regulator (CHD1). Furthermore, we have also found that ethanol stimulates hyperfilamentation in diploid cells, again in a MA PK-dependent manner. Together, these results suggest that yeast may sense a combination of nutrient limitation and metabolic by-products to regulate d ifferentiation.