Channel-Like Characteristics of the Low-Affinity Barley Phosphate Transporter PHT1;6 When Expressed inXenopusOocytes

Abstract

Remobilization of inorganic phosphate (P i ) within a plant is critical for sustaining growth and seed production under external P i fluctuation. The barley (Hordeum vulgare) transporter HvPHT1;6 has been implicated in P i remobilization. In this report, we expressed HvPHT1;6 in Xenopus laevis oocytes, allowing detailed characterization of voltage-dependent fluxes and currents induced by HvPHT1;6. HvPHT1;6 increased efflux of P i near oocyte resting membrane potentials, dependent on external P i concentration. Time-dependent inward currents were observed when membrane potentials were more negative than 2160 mV, which was consistent with nH + :HPO 4 22 (n . 2) cotransport, based on simultaneous radiotracer and oocyte voltage clamping, dependent upon P i concentration gradient and pH. Time-and voltage-dependent inward currents through HvPHT1;6 were also observed for SO 4 22, and to a lesser degree for NO 3 2 and Cl 2, but not for malate. Inward and outward currents showed linear dependence on the concentration of external HPO 4 22 , similar to low-affinity P i transport in plant studies. The electrophysiological properties of HvPHT1;6, which locates to the plasma membrane when expressed in onion (Allium cepa) epidermal cells, are consistent with its suggested role in the remobilization of P i in barley plants.

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

“…Expression Levels of the Genes Related to Low-Affinity Pi Transporters Are Correlated with PUE HvPHT1;6 is a low-affinity Pi transporter (Preuss et al, 2010). It is expressed in both shoots and roots (Huang et al, 2008) and especially in phloem tissues of the leaf (Rae et al, 2003), suggesting that HvPHT1;6 plays a role in Pi remobilization in the whole plant.…”

“…HvPHT1;6 is expressed in both shoots and roots (Huang et al, 2008) and localized in the leaf phloem tissue (Rae et al, 2003). It displays unsaturated uptake in a millimolar range of Pi concentrations when expressed in oocytes (Preuss et al, 2010), suggesting that HvPHT1;6 is involved in Pi retranslocation. HvPHT1;7 is specifically expressed in green anthers (Druka et al, 2006), and HvPHT1;8 is a mycorrhiza-specific gene (Glassop et al, 2005).…”

“…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.…”

Structure and Expression Profile of the Phosphate Pht1 Transporter Gene Family in Mycorrhizal Populus trichocarpa

“…In annual plants, Himelblau and Amasino (2001) have found that about 80% of P is removed from senescing Arabidopsis (Arabidopsis thaliana) leaves. In barley (Hordeum vulgare), expression of the Pi transporter HvPT6, likely involved in Pi remobilization (Preuss et al, 2010), was increased as leaves aged (Rae et al, 2003).…”

A Constitutive Expressed Phosphate Transporter, OsPht1;1, Modulates Phosphate Uptake and Translocation in Phosphate-Replete Rice

“…Recently, Nagarajan et al (2011) reported that the Arabidopsis pht1;5-1 mutant had higher shoot P content compared with the wild type, while the P content in roots was reduced under Pi-replete conditions, suggesting that Pht1;5 may mobilize Pi between source and sink tissues. In addition, Preuss et al (2010) explored the characteristics of the low-affinity barley (Hordeum vulgare) PiT PHT1;6 using the Xenopus laevis oocyte expression system, implying that it may play a Pi-transport role at Pi-sufficient conditions in plants.…”