Protein Phosphatase OsPP95 Regulates Phosphate Uptake And Remobilization By Affecting The Trafficking Of Phosphate Transporters In Rice

Phosphorus is an essential nutrient element for plant growth and development.Plant phosphate uptake is largely dependent on plasma membrane(PM)-localized Pi transporters(PTs).PTs trafficking from the endoplasmic reticulum(ER)to the PM requires the function of PHF1(PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR 1),a Sec12-related protein that facilitates PT exit from the ER.PTs are subject to phosphorylation modification which affects is trafficking from the ER to the PM in response to Pi status in Arabidopsis and rice.Previous study indicates that rice CK2(CASEIN KINASE2)could phosphorylates OsPT2 and OsPT8,impairing their interaction with OsPHF1 and resulting in retention of PTs in the ER.Protein phosphorylation is a reversible post-translational modification which is mediated by protein kinase and protein phosphatase and plays critical roles in protein localization,stability,and activity.However,whether there is a protein that dephosphorylates PTs is not known.Here,we identified a PP2 C type protein phosphatase,OsPP95,which interacted with OsPT2 and OsPT8 in vivo and in vitro.OsPP95 dephosphorylates OsPT8 at Ser-517,the same amino acid that could be phosphorylated by OsCK2.Overexpression of OsPP95 reduced the phosphorylation level of OsPT8,promoted the trafficking of OsPT2 and OsPT8 from the ER to the PM,and resulted in Pi accumulation in rice plant.Mutation of OsPP95 did not change the Pi level of the whole plant under Pi-sufficient condition,however,reduced Pi concentration in the youngest leaf and increased Pi accumulation in the old leaves compared to WT.Furthermore,our data showed that more OsPP95 protein was accumulated in plants grown under Pi-starvation condition compared to Pi-sufficient condition due to the rapid degradation of OsPP95 under Pi-sufficient condition.In addition,our data further indicated that OsPHO2 could interact with and degrade OsPP95.Taken together,our results indicate that OsPP95,a protein phosphatase negatively regulated by OsPHO2,positively regulate Pi uptake and remobilization through dephosphorylating PTs and affecting its trafficking to PM.This work uncovers a reversible PT phosphorylation mechanism that is essential for plants adaption to variable Pi environment.