Vacuolar phosphate efflux transporter ZmVPEs mediate phosphate homeostasis and remobilization in maize leaves

Phosphorus(P) is an essential macronutrient for plant growth and development. Vacuoles play a crucial role in inorganic phosphate(Pi) storage and remobilization in plants. However, the physiological function of vacuolar phosphate efflux transporters in plant Pi remobilization remains obscure. Here, we identified three Zm VPE genes(ZmVPE1, ZmVPE2a, ZmVPE2b) by combining them with transcriptome and quantitative real-time polymerase chain reaction(PCR) analyses,showing a relatively higher expression in older leaves than in younger leaves in maize. Moreover,the expression of the ZmVPEs was triggered by Pi deficiency and abscisic acid. ZmVPEs were localized to the vacuolar membrane and responsible for vacuolar Pi efflux. Compared with the wild-type, Pi remobilization from older to younger leaves was enhanced in Zm VPE-overexpression lines. zmvpe2a mutants displayed an increase in the total P and Pi concentrations in older leaves, but a decrease in younger leaves. In rice, Pi remobilization was impaired in the osvpe1osvpe2 double mutant and enhanced in OsVPE-overexpression plants, suggesting conserved functions of VPEs in modulating Pi homeostasis and remobilization in crop plants. Taken together, our findings revealed a novel mechanism underlying Pi remobilization from older to younger leaves mediated by plant vacuolar Pi efflux transporters, facilitating the development of Pi-efficient crop plants.