Identification of plant vacuolar transporters mediating phosphate storage

Plant vacuoles serve as the primary intracellular compartments for inorganic phosphate (Pi) storage. Passage of Pi across vacuolar membranes plays a critical role in buffering the cytoplasmic Pi level against fluctuations of external Pi and metabolic activities. Here we demonstrate that the SPX-MFS proteins, designated as Phosphate Transporter 5 family (PHT5), also named Vacuolar Phosphate Transporter (VPT), function as vacuolar Pi transporters. Based on 31P-magnetic resonance spectroscopy analysis, Arabidopsis pht5;1 loss-of-function mutants accumulate less Pi and exhibit a lower vacuolar-to-cytoplasmic Pi ratio than controls. Conversely, overexpression of PHT5 leads to massive Pi sequestration into vacuoles and altered regulation of Pi starvation-responsive genes. Furthermore, we show that heterologous expression of OsSPX-MFS1, the rice PHT5 homolog, mediates Pi influx to yeast vacuoles. Our findings uncover a group of Pi transporters in vacuolar membranes that regulate the cytoplasmic Pi homeostasis required for the fitness of plant growth. Overall design: 10-day seedlings grown on Pi-sufficient medium or followed by 1-day or 3-day Pi starvation, shoot RNA and root RNA were extracted separately