A conserved Pho4-Pho84 axis ubiquitously maintains intracellular phosphate homeostasis in yeast

Inorganic phosphate (Pi) is central to fundamental cellular processes and the metabolic economy, and is constantly acquired in order to maintain intracellular Pi levels. While much is known about cellular adaptation during Pi starvation, how intracellular Pi is maintained in Pi-replete conditions remains unclear. Here, using Saccharomyces cerevisiae, we uncover an essential role for the Pho4 transcription factor in maintaining intracellular Pi under Pi-replete conditions, via the high affinity Pho84 transporter. Basal Pho4-dependent output is required for intracellular Pi maintenance, and the loss of Pho4 results in decreased intracellular Pi. We uncover that the Pho4 dependent, high affinity Pi transporter Pho84 is the primary transporter required for this intracellular Pi maintenance in phosphate replete conditions, and is not compensated by other transporters. The loss of Pho4 or Pho84 decreases intracellular Pi, with reduced ATP and glycolysis, and decreased growth. Through comparative genomic and phylogenetic analyses we establish that Pho84 is universally conserved across fungi, and Pho84 alone is orthologous to the plant high-affinity phosphate transporter PHT1. Thus, Pho84 is a primary determinant of intracellular Pi homeostasis during phosphate replete growth, and Pi acquisition in replete conditions is built around high-affinity phosphate transport. These findings reiterate the importance of Pi acquisition via high-affinity transport for metabolic homeostasis, with implications for microbial fermentation-based applications.