A vacuolar phosphate transporter essential for phosphate homeostasis inArabidopsis

Abstract

Inorganic phosphate (Pi) is stored in the vacuole, allowing plants to adapt to variable Pi availability in the soil. The transporters that mediate Pi sequestration into vacuole remain unknown, however. Here we report the functional characterization of Vacuolar Phosphate Transporter 1 (VPT1), an SPX domain protein that transports Pi into the vacuole in Arabidopsis. The vpt1 mutant plants were stunted and consistently retained less Pi than wild type plants, especially when grown in medium containing high levels of Pi. In seedlings, VPT1 was expressed primarily in younger tissues under normal conditions, but was strongly induced by high-Pi conditions in older tissues, suggesting that VPT1 functions in Pi storage in young tissues and in detoxification of high Pi in older tissues. As a result, disruption of VPT1 rendered plants hypersensitive to both low-Pi and high-Pi conditions, reducing the adaptability of plants to changing Pi availability. Patch-clamp analysis of isolated vacuoles showed that the Pi influx current was severely reduced in vpt1 compared with wild type plants. When ectopically expressed in Nicotiana benthamiana mesophyll cells, VPT1 mediates vacuolar influx of anions, including Pi, SO42−, NO3−, Cl−, and malate with Pi as that preferred anion. The VPT1-mediated Pi current amplitude was dependent on cytosolic phosphate concentration. Single-channel analysis showed that the open probability of VPT1 was increased with the increase in transtonoplast potential. We conclude that VPT1 is a transporter responsible for vacuolar Pi storage and is essential for Pi adaptation in Arabidopsis.

Vacuolar SPX-MFS transporters are essential for phosphate adaptation in plants

“…When ectopically expressed in the vacuoles of Nicotiana benthamiana mesophyll cells, VPT1 could mediate several anions influx across the tonoplast, including Pi, SO 4 2¡ , NO 3 ¡ , Cl ¡ , and malate with Pi as that preferred anion. 3 Complementary to our results, 31 P-magnetic resonance spectroscopy analysis revealed that loss-of-function of vpt1 mutants accumulated less Pi and exhibited a lower vacuolar-to-cytoplasmic Pi ratio than the wild types. 4 Taken together, these results indicate that the members of SPX-MFS family are the candidate transporters conducting Pi across the tonoplast.…”

“…6 We found that the transgenic plants expressing At1g63010 with a green fluorescent protein (GFP) fusion displayed the fluorescent signals specifically detected in the tonoplast, and thus named this gene as VPT1 (Vacuolar Phosphate Transporter 1). 3 The subcellular location of VPT1 in the tonoplast was further confirmed in an independent study, where it was named as PHT5;1 (PHOSPHATE TRANSPORTER 5;1).…”

“…During most phases of plant development, Pi concentration is much higher in the vacuole than in the cytosol, indicating that the vacuole has transport proteins responsible for the transport of Pi across tonoplast. 2 Recently, we, 3 Liu et al, 4 and Wang et al 5 independently revealed that SPX-MFS family potentially might function as a new group of vacuolar Pi transporters in plants. SPX-MFS proteins contain an evolutionally conserved SPX domain [named after yeast Syg1 and Pho81 and human xenotropic and polytropic retrovirus receptor 1 (XPR1)] with an MFS (Major Facilitator Superfamily) domain.…”

Purification and functional characterization of the vacuolar malate transporter tDT from Arabidopsis

“…This inability of tDT to accept sulphate and phosphate as substrates concurs, however, with the presence of specific PO 4 2--and SO 4 2-carriers in the vacuolar membrane (33,34). It appears likely that the functions of the latter carriers in controlling cellular phosphate-and sulphate homeostasis would be hampered by the simultaneous presence of additional carboxylate/SO 4 2--or carboxylate/PO 4 2--transport capacity across the tonoplast.…”

Phosphorus Transport in Arabidopsis and Wheat: Emerging Strategies to Improve P Pool in Seeds

“…In contrast, PHT2 proteins are localized in chloroplasts, while PHT3/MPT proteins are mostly mitochondrial membrane transporters and PHT4 proteins are Golgi-apparatus located transporters. A vacuolar Pi transporter was identified in Arabidopsis and designated as PHT5/VPT/SPX-MFS proteins [26].…”