Inorganic phosphate is sensed by specific phosphate carriers and acts in concert with glucose as a nutrient signal for activation of the protein kinase A pathway in the yeast Saccharomyces cerevisiae

Abstract

SummaryYeast cells starved for inorganic phosphate on a glucose-containing medium arrest growth and enter the resting phase G0. We show that re-addition of phosphate rapidly affects well known protein kinase A targets: trehalase activation, trehalose mobilization, loss of heat resistance, repression of STREcontrolled genes and induction of ribosomal protein genes. Phosphate-induced activation of trehalase is independent of protein synthesis and of an increase in ATP. It is dependent on the presence of glucose, which can be detected independently by the Gprotein coupled receptor Gpr1 and by the glucosephosphorylation dependent system. Addition of phosphate does not trigger a cAMP signal. Despite this, lowering of protein kinase A activity by mutations in the TPK genes strongly reduces trehalase activation. Inactivation of phosphate transport by deletion of PHO84 abolishes phosphate signalling at standard concentrations, arguing against the existence of a transport-independent receptor. The nonmetabolizable phosphate analogue arsenate also triggered signalling. Constitutive expression of the Pho84, Pho87, Pho89, Pho90 and Pho91 phosphate carriers indicated pronounced differences in their transport and signalling capacities in phosphatestarved cells. Pho90 and Pho91 sustained highest phosphate transport but did not sustain trehalase activation. Pho84 sustained both transport and rapid signalling, whereas Pho87 was poor in transport but positive for signalling. Pho89 displayed very low phosphate transport and was negative for signalling. Although the results confirmed that rapid signalling is independent of growth recovery, long-term mobilization of trehalose was much better correlated with growth recovery than with trehalase activation. These results demonstrate that phosphate acts as a nutrient signal for activation of the protein kinase A pathway in yeast in a glucose-dependent way and they indicate that the Pho84 and Pho87 carriers act as specific phosphate sensors for rapid phosphate signalling.

Arbuscular Mycorrhizal Symbiosis Requires a Phosphate Transceptor in the Gigaspora margarita Fungal Symbiont

“…GigmPT also shows sequence and structural similarities to the yeast Pho84 sensor ( Giots et al, 2003 andPopova et al, 2010). Based on these similarities, we further determined whether GigmPT could act as both a transporter and a receptor, or a "transceptor," in yeast.…”

Identification of Genes Affecting Lipid Content Using Transposon Mutagenesis inSaccharomyces cerevisiae

“…PRE9 encoding an ubiquitin-dependent endopeptidase of the 20S proteasome 29) might degrade proteins to retrieve nitrogen sources, and hence can affect the balance of carbon sources and nitrogen sources, which regulates lipid accumulation. 30) PHO90 encoding a phosphate transporter 31) is involved in phosphate-induced signaling in concert with glucose, 32) raising the possibility that PHO90 is involved in lipid accumulation by phosphate depletion. Finally, SPT21 encoding a regulator of transcription 33) might negatively regulate transcription of genes involved in lipid accumulation.…”

A Plasma Membrane Association Module in Yeast Amino Acid Transporters

“…The KPRWYR motif in the C terminus of Gap1 has been shown to be important for trafficking from the trans-Golgi network to the PM (19). In addition, a dileucine motif in a predicted ␣-helical region of the Gap1 C terminus is required for NH 4 ϩ -induced endocytosis (25,36). Deletion of the last 28 residues of Bap2 was shown to stabilize the protein at the plasma membrane by decreasing its basal turnover (28).…”

“…E-mail: b.poolman@rug.nl. 4 The abbreviations used are: PM, plasma membrane; VM, vacuolar membrane; APC, amino acid/polyamine/organocation; MFS, major facilitator superfamily; AAPTII, amino acid/polyamine transporter II; AAP, amino acid permease; ER, endoplasmic reticulum; NLS, nuclear localization signal; cNLS, classical nuclear localization signal; tcNLS, tandem classical NLS; FRAP, fluorescence recovery after photobleaching; MCC, microcompartment of Can1. …”

“…The most prominent example is Gap1, which has a receptor function whereby it signals the protein kinase A (PKA) pathway (3). This so-called transceptor function has also been described for the phosphate transporter Pho84 and the ammonium transporter Mep2 but not for any other AAPs (4,5). On the other end of the spectrum is Ssy1, an endoplasmic reticulum (ER)-resident AAP member, that plays a role in amino acid sensing but has no transport function (6 -8).…”