Abstract
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.
Highlights
Phosphorus (P) is an essential mineral nutrient for plant development and reproduction and an integral component of biomacromolecules such as phospholipids and nucleic acids
OsPP95 Physically Interacts with Pi transporters (PTs) To investigate whether protein phosphatase is responsible for the dephosphorylation of PTs and affects their endoplasmic reticulum (ER) exit and trafficking to the plasma membrane (PM), we investigated the subcellular localizations of GFP-tagged OsPT2 and OsPT8 treated with or without a general protein phosphatase inhibitor (Supplemental Figure 1)
In contrast to untreated plants, in which most OsPT8-GFP was localized to the PM, OsPT8-GFP was detected in the ER after treatment with protein phosphatase inhibitor, resembling the localization of OsPT8GFP in the OsCK2α3 overexpression line
Summary
Phosphorus (P) is an essential mineral nutrient for plant development and reproduction and an integral component of biomacromolecules such as phospholipids and nucleic acids. Rice PHT1 genes show different tissue-specific expression patterns and responses to Pi starvation, and encode enzymes with different affinities for Pi. For instance, the high-affinity Pi transporter OsPT8 (PHOSPHATE TRANSPORTER 8) is not responsive to Pi starvation at the transcriptional level but is universally expressed in rice tissues and plays an important role in Pi uptake (Chen et al, 2011; Jia et al, 2011). The low-Pi-induced transporter OsPT2, which is localized in the stele of roots, plays important roles in Pi uptake and root-to-shoot translocation under Pi-deficient conditions (Ai et al, 2009). Other functionally characterized PHT1 genes including OsPT3/6/9/10 are induced by low Pi and play diverse roles in Pi uptake and translocation (Ai et al, 2009; Sun et al, 2012; Wang et al, 2014; Chang et al, 2019)
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