Phosphite disrupts the acclimation of Saccharomyces cerevisiae to phosphate starvation

The influence of phosphite (H2PO3-) on the response of Saccharomyces cerevi siae to orthophosphate (HPO42-; P-i) starvation was assessed. Phosphate-rep ressible acid phosphatase (rAPase) derepression and cell development were a bolished when phosphate-sufficient (+P-i) yeast were subcultured into phosp hate-deficient (-P-i) media containing 0.1 mM phosphite. By contrast, treat ment with 0.1 mM phosphite exerted no influence on rAPase activity or growt h of +P-i cells. P-31 NMR spectroscopy revealed that phosphite is assimilat ed and concentrated by yeast cultured with 0.1 mM phosphite, and that the l evels of sugar phosphates, pyrophosphate, and particularly polyphosphate we re significantly reduced in the phosphite-treated -P-i cells. Examination o f phosphite's effects on two PHO regulon mutants that constitutively expres s 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 mechan ism exists to control rAPase expression that is independent of Pho85 (cycli n-dependent protein kinase). Marked accumulation of polyphosphate in the De ltapho85 mutant suggested that Pho85 contributes to the control of polyphos phate metabolism. Results are consistent with the hypothesis that phosphite obstructs the signaling pathway by which S. cerevisiae perceives and respo nds to phosphate deprivation at the molecular level.