Glucose depletion causes haploid invasive growth in yeast

Haploid yeast invades solid agar in response to nutrient limitation. To dec ipher the cues that underlie invasion, we have developed a single cell inva sive growth assay. Using this assay, as well as the traditional plate-washi ng assay, we show that invasive growth occurs in response to glucose deplet ion. in the absence of glucose (or other fermentable sugar), individual cel ls adopted a nonaxial budding pattern and elongated morphology within the f irst cell divisions, and invasion into the agar was observed in microcoloni es containing as few as 10 cells. In support of this observation, we found that glucose suppressed the hyperinvasive growth morphology of STE11-4 pbs2 . hsl7, and RAS2V19 mutations. In addition, removal of glucose from YPD med ium caused constitutive invasion in wild-type cells. We tested glucose cont rol proteins for a role in invasion and found that Snf1, a protein required for derepression of glucose-repressed genes, was required for invasive gro wth. The transcription factor Sip4 which interacts with Snf1 and is induced during the diauxic shift, had an inhibitory role on invasive growth, sugge sting that multiple mechanisms are required for glucose depletion-dependent invasion.