Proton-coupled high-affinity phosphate transport revealed from heterologous characterization in Xenopus of barley-root plasma membrane transporter, HvPHT1;1

Abstract

High-affinity phosphate transporters mediate uptake of inorganic phosphate (Pi) from soil solution under low Pi conditions. The electrophysiological properties of any plant high-affinity Pi transporter have not been described yet. Here, we report the detailed characterization of electrophysiological properties of the barley Pi transporter, HvPHT1;1 in Xenopus laevis oocytes. A very low Km value (1.9 µm) for phosphate transport was observed in HvPHT1;1, which falls within the concentration range observed for barley roots. Inward currents at negative membrane potentials were identified as nH+:Pi- (n > 1) co-transport based on simultaneous Pi radiotracer uptake, oocyte voltage clamping and pH dependence. HvPHT1;1 showed preferential selectivity for Pi and arsenate, but no transport of the other oxyanions SO42− and NO3-. In addition, HvPHT1;1 locates to the plasma membrane when expressed in onion (Allium cepa L.) epidermal cells, and is highly expressed in root segments with dense hairs. The electrophysiological properties, plasma membrane localization and cell-specific expression pattern of HvPHT1;1 support its role in the uptake of Pi under low Pi conditions.