Identification of vacuolar phosphate efflux transporters in land plants

Inorganic phosphate (Pi) is an essential component of all life forms. Land plants acquire Pi from the soil through roots and associated symbioses, and it is then transported throughout the plant. When sufficient, excess Pi is stored in vacuoles for remobilization following Pi deficiency. Although Pi release from the vacuoles to the cytoplasm serves as a critical mechanism for plants to adapt to low-Pi stress, the transporters responsible for vacuolar Pi efflux have not been identified. Here, we identified a pair of Oryza sativa vacuolar Pi efflux transporters (OsVPE1 and OsVPE2) that were more abundant in plants grown under Pi-deficient conditions. These OsVPE proteins can transport Pi into yeast cells and Xenopus laevis oocytes. Vacuolar Pi content was higher in the loss-of-function Osvpe1 Osvpe2 double mutant than in wild type, particularly under low-Pi stress. Overexpression of either OsVPE1 or OsVPE2 in transgenic plants reduced vacuolar Pi content, consistent with a role in vacuolar Pi efflux. We demonstrate that these VPE proteins evolved from an ancient plasma membrane glycerol-3-phosphate transporter protein. Together, these data indicate that this transporter was recruited to the vacuolar membrane to catalyse Pi efflux during the course of land plant evolution. Phosphorus is one of the essential nutrients for all living organisms. Plants and fungi store phosphate in their vacuoles. Multiple plant influx transporters have been reported to import phosphate to the vacuoles. Now, two new phosphate efflux transporters are shown to be important for phosphate export from the vacuole in rice and probably other land plants.