Glucose depletion causes haploid invasive growth in yeast

Abstract

Haploid yeast invades solid agar in response to nutrient limitation. To decipher the cues that underlie invasion, we have developed a single cell invasive growth assay. Using this assay, as well as the traditional plate-washing assay, we show that invasive growth occurs in response to glucose depletion. In the absence of glucose (or other fermentable sugar), individual cells adopted a nonaxial budding pattern and elongated morphology within the first cell divisions, and invasion into the agar was observed in microcolonies 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 medium caused constitutive invasion in wild-type cells. We tested glucose control proteins for a role in invasion and found that Snf1, a protein required for derepression of glucose-repressed genes, was required for invasive growth. The transcription factor Sip4, which interacts with Snf1 and is induced during the diauxic shift, had an inhibitory role on invasive growth, suggesting that multiple mechanisms are required for glucose depletion-dependent invasion. S everal yeast͞fungal species have the ability to adopt two growth forms, a vegetative (yeast) form and a pseudohyphal or filamentous form. In pathogenic organisms such as Candida albicans, this morphological transition is important for invasion of host tissue and therefore pathogenesis (1). In nonpathogenic organisms, the transition can occur upon nutrient limitation and has therefore been suggested to be a mechanism to permit foraging for nutrients. Insight into the signal transduction mechanisms that are necessary for the morphological change will contribute to an understanding of basic biological phenomena and of pathogenesis.The budding yeast Saccharomyces cerevisiae provides a genetic system to investigate the morphological transition from vegetative to filamentous development. In diploid yeast, loss of environmental fixed nitrogen causes the transition from vegetative growth, in which cells are round and bud in a bipolar fashion, to pseudohyphal growth, in which cells are elongated and bud in a unipolar budding pattern (2). In haploid yeast, nutrient limitation causes a similar developmental switch that allows cells to penetrate the surface of an agar medium in a process called invasive growth (see refs. 3-6 for reviews). For simplicity, we will use the term filamentous form to refer to both pseudohyphal and invasive growth, although there are differences between these two growth responses.At least two signal transduction pathways are required for filamentous growth. One pathway uses a number of components from the pheromone response pathway, notably the p21-activated kinase (PAK) kinase Ste20, the kinases Ste11 and Ste7 from the first two tiers of the mitogen-activated protein (MAP) kinase cascade, and the transcription factor Ste12 (7, 8), but has unique components as well-the MAP kinase Kss1 (9-11) and a second t...

Phosphoproteomic identification of targets of the Arabidopsis sucrose nonfermenting-like kinase SnRK2.8 reveals a connection to metabolic processes

“…50 mg of leaves from wild type and snrk2.8-1 Ϯ NaCl treatment for 3 days were homogenized in 1 ml of 0.1 M sodium phosphate buffer (pH 7.0) containing 0.811 mM MgSO 4 and 20% glycerol and centrifuged at 50,000 ϫ g for 20 min. For assays of glyI activity in plant extracts, supernatant was diluted with potassium phosphate buffer (pH 6.6) and 0.2% (vol/vol) methylglyoxyal solution, and reduced glutathione was added as substrates.…”

“…AMPK is implicated in the development and treatment of metabolic disorders, including obesity and type 2 diabetes (2), and mutations in AMPK causes cardiac abnormalities (3). In yeast, SNF1 is required for regulation of glucose-responsive genes necessary for pseudohyphal growth in response to nutrient limitations (4) and for controlling the onset of meiosis in yeast (5). SNF1 provides a mechanism for crosstalk between metabolic pathways and cell cycle signaling processes (6).…”

In Saccharomyces cerevisiae an unbalanced level of tyrosine phosphorylation down-regulates the Ras/PKA pathway

“…Different environmental stimuli induce dimorphic switch in haploids (invasive growth) and diploids (pseudohyphal growth) cells. The triggering signal appears to be glucose starvation in haploids (Cullen & Sprague, 2000;Roberts & Fink, 1994) and nitrogen starvation in diploids (Gimeno et al, 1992). In both cases, a major alteration in cell morphology is observed so that cells become elongated and do not separate after cytokinesis, generating cell chains that invade the growth substrate.…”

Reversible induction of translational isoforms of p53 in glucose deprivation

“…Methionine synthase, a key enzyme that clears intracellular homocysteine, is induced by its cofactor, vitamin B12, at a translational level through an IRES in the 5'UTR of the mRNA. 26 In response to glucose deprivation, haploid Saccharomyces cerevisiae cells dramatically downregulate translation of most cellular messages, 27,28 but several yeast genes required for invasive growth, a developmental pathway induced by nutrient limitation, contain potent IRESs. 29 Serum starvation of mammalian cell cultures showed induction of Bcl-2 IRES 30 and activated translation of XIAP mRNA.…”