Phosphite disrupts the acclimation of Saccharomyces cerevisiae to phosphate starvation

The influence of phosphite (H2PO3-) on the response of Saccharomyces cerevisiae to orthophosphate (HPO42-; P-i) starvation was assessed. Phosphate-repressible acid phosphatase (rAPase) derepression and cell development were abolished when phosphate-sufficient (+P-i) yeast were subcultured into phosphate-deficient (-P-i) media containing 0.1 mM phosphite. By contrast, treatment with 0.1 mM phosphite exerted no influence on rAPase activity or growth of +P-i cells. P-31 NMR spectroscopy revealed that phosphite is assimilated and concentrated by yeast cultured with 0.1 mM phosphite, and that the levels of sugar phosphates, pyrophosphate, and particularly polyphosphate were significantly reduced in the phosphite-treated -P-i cells. Examination of phosphite's effects on two PHO regulon mutants that constitutively express rAPase indicated that (i) a potential target for phosphite's action in -P-i yeast is Pho84 (plasmalemma high-affinity P-i transporter and component of a putative phosphate sensor-complex), and that (ii) an additional mechanism exists to control rAPase expression that is independent of Pho85 (cyclin-dependent protein kinase). Marked accumulation of polyphosphate in the Deltapho85 mutant suggested that Pho85 contributes to the control of polyphosphate metabolism. Results are consistent with the hypothesis that phosphite obstructs the signaling pathway by which S. cerevisiae perceives and responds to phosphate deprivation at the molecular level.