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 mM) 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 SO4 2-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.

Phosphate Utilization Efficiency Correlates with Expression of Low-Affinity Phosphate Transporters and Noncoding RNA, IPS1, in Barley

“…The promoter::reporter fusions of HvPHT1;1 and HvPHT1;2 show that reporters are expressed in root hairs, epidermal and cortex cells, and vascular tissues of roots (Schü nmann et al, 2004;Glassop et al, 2005). Recently, it was confirmed that HvPHT1;1 is a high-affinity Pi transporter with a K m of 1.9 mM when expressed in Xenopus laevis oocytes (Preuss et al, 2011), suggesting that HvPHT1;1 is involved in Pi acquisition. HvPHT1;6 is expressed in both shoots and roots (Huang et al, 2008) and localized in the leaf phloem tissue (Rae et al, 2003).…”

“…Our recent work revealed that HvPHT1;1 is a highaffinity Pi transporter with a K m value of 1.9 mM when expressed in Xenopus oocytes (Preuss et al, 2011). Higher transcript abundance of HvPHT1;1 is found in the root hair zone than in the root tip (Preuss et al, 2011). The expression pattern of HvPHT1;1 in root tissues overlaps with HvPHT1;2 (Schü nmann et Glassop et al, 2005), suggesting that both HvPHT1;1 and HvPHT1;2 are involved in P acquisition.…”

“…S2). Our recent work revealed that HvPHT1;1 is a highaffinity Pi transporter with a K m value of 1.9 mM when expressed in Xenopus oocytes (Preuss et al, 2011). Higher transcript abundance of HvPHT1;1 is found in the root hair zone than in the root tip (Preuss et al, 2011).…”

“…RNA isolation and real-time quantitative RT-PCR analysis of transcripts were conducted as described by Preuss et al (2011). Briefly, total RNA from roots was prepared using Trizol reagent according to the manufacturer's instructions (Invitrogen) and treated with DNase I (Ambion).…”

“…To address this issue, we used barley, a diploid relative of hexaploid wheat, as a model system for winter cereals to study the functions of PHT1 genes involved in the acquisition and remobilization of Pi (Preuss et al, 2010(Preuss et al, , 2011. In this report, we show that differences in expression levels of four paralogs of the high-affinity Pi transporter gene HvPHT1;1, are not apparent among four barley genotypes differing in PAE, but there is a large difference in the expression of the lowaffinity Pi transporter HvPHT1;6 and a close homolog, HvPHT1;3.…”