PROTEIN PHOSPHATASE95 Regulates Phosphate Homeostasis by Affecting Phosphate Transporter Trafficking in Rice

Phosphate (Pi) uptake in plants depends on plasma membrane (PM)-localized phosphate transporters (PTs). OsCK2 phosphorylates PTs and inhibits their trafficking from the endoplasmic reticulum (ER) to the PM in rice (Oryza sativa), but how PTs are dephosphorylated is unknown. We demonstrate that the protein phosphatase type 2C (PP2C) protein phosphatase OsPP95 interacts with OsPT2 and OsPT8 and dephosphorylates OsPT8 at Ser-517. Rice plants overexpressing OsPP95 reduced OsPT8 phosphorylation and promoted OsPT2 and OsPT8 trafficking from the ER to the PM, resulting in Pi accumulation. Under Pi-sufficient conditions, Pi levels were lower in young leaves and higher in old leaves in ospp95 mutants than in those of the wild type, even though the overall shoot Pi levels were the same in the mutant and the wild type. In the wild type, OsPP95 accumulated under Pi starvation but was rapidly degraded under Pi-sufficient conditions. We show that OsPHO2 interacts with and induces the degradation of OsPP95. We conclude that OsPP95, a protein phosphatase negatively regulated by OsPHO2, positively regulates Pi homeostasis and remobilization by dephosphorylating PTs and affecting their trafficking to the PM, a reversible process required for adaptation to variable Pi conditions.