title: Stable Pseudohyphal Growth in Budding Yeast Induced by Synergism between Septin Defects and Altered MAP-kinase Signaling.
abstract: Upon nutrient limitation, budding yeasts like Saccharomyces cerevisiae can be induced to adopt alternate filament-like growth patterns called diploid pseudohyphal or invasive haploid growth. Here, we report a novel constitutive pseudohyphal growth state, sharing some characteristics with classic forms of filamentous growth, but differing in crucial aspects of morphology, growth conditions and genetic regulation. The constitutive pseudohyphal state is observed in fus3 mutants containing various septin assembly defects, which we refer to as sadF growth (septin assembly defect induced filamentation) to distinguish it from classic filamentation pathways. Similar to other filamentous states, sadF cultures comprise aggregated chains of highly elongated cells. Unlike the classic pathways, sadF growth occurs in liquid rich media, requiring neither starvation nor the key pseudohyphal proteins, Flo8p and Flo11p. Moreover sadF growth occurs in haploid strains of S288C genetic background, which normally cannot undergo pseudohyphal growth. The sadF cells undergo highly polarized bud growth during prolonged G2 delays dependent on Swe1p. They contain septin structures distinct from classical pseudo-hyphae and FM4-64 labeling at actively growing tips similar to the Spitzenkörper observed in true hyphal growth. The sadF growth state is induced by synergism between Kss1p-dependent signaling and septin assembly defects; mild disruption of mitotic septins activates Kss1p-dependent gene expression, which exacerbates the septin defects, leading to hyper-activation of Kss1p. Unlike classical pseudo-hyphal growth, sadF signaling requires Ste5, Ste4 and Ste18, the scaffold protein and G-protein β and γ subunits from the pheromone response pathway, respectively. A swe1 mutation largely abolished signaling, breaking the positive feedback that leads to amplification of sadF signaling. Taken together, our findings show that budding yeast can access a stable constitutive pseudohyphal growth state with very few genetic and regulatory changes.
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America.
authors.forename: Junwon
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Rose
mesh_terms: D002453:Cell Cycle / Q000235:genetics*; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics; D002455:Cell Division / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal; D006238:Haploidy; D025301:Hyphae / Q000235:genetics* / Q000254:growth & development; D020935:MAP Kinase Signaling System / Q000235:genetics; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics; D020928:Mitogen-Activated Protein Kinases / Q000737:chemistry / Q000235:genetics; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics; D011505:Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics; D058112:Septins / Q000737:chemistry / Q000235:genetics*; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics
chemical_list: D018797:Cell Cycle Proteins; C110690:FLO11 protein, S cerevisiae; C100940:FLO8 protein, S cerevisaie; D008562:Membrane Glycoproteins; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; C099685:SWE1 protein, S cerevisiae; D011505:Protein-Tyrosine Kinases; C075580:FUS3 protein, S cerevisiae; C541984:KSS1 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; D058112:Septins