MADS Box Transcription Factor Mbx2/Pvg4 Regulates Invasive Growth and Flocculation by Inducinggsf2+Expression in Fission Yeast

Abstract

ABSTRACTThe fission yeastSchizosaccharomyces pombeexhibits invasive growth and nonsexual flocculation in response to nitrogen limitation. Gsf2, a flocculin of fission yeast, is required not only for nonsexual flocculation but also for invasive growth through the recognition of galactose residues on cell surface glycoconjugates. We found that pyruvylation negatively regulates nonsexual flocculation by capping the galactose residues ofN-linked galactomannan. We investigated whether pyruvylation also regulates invasive growth. Thepvg4+gene originally was isolated as a multicopy suppressor of apvg4mutant defective in the pyruvylation ofN-linked oligosaccharides. However, we did not detect a defect in cell surface pyruvylation in thepvg4/mbx2deletion mutant, as assessed by alcian blue staining and a Q-Sepharose binding assay. Instead, the deletion prevented invasive growth under conditions of low nitrogen and high glucose, and it reduced the adhesion and flocculation of otherwise flocculent mutants by reducinggsf2+expression.mbx2+-overexpressing strains exhibited nonsexual and calcium-dependent aggregation, which was inhibited in the presence of galactose but mediated by the induction ofgsf2+. These findings indicate that Mbx2 mediates invasive growth and flocculation via the transcriptional activation ofgsf2+in fission yeast. In addition, we found that fission yeast Mbx2 induces the nonsexual flocculation of budding yeast by the activation ofFLO1.