Complementary structures of the yeast phosphate transporter Pho90 provide insights into its transport mechanism.

Phosphate homeostasis is essential for all living organisms. Low-affinity phosphate transporters are involved in phosphate import and regulation in a range of eukaryotic organisms. We have determined the structures of the Saccharomyces cerevisiae phosphate importer Pho90 by electron cryomicroscopy in two complementary states at 2.3 and 3.1 Å resolution. The symmetrical, outward-open structure in the presence of phosphate indicates bound substrate ions in the binding pocket. In the absence of phosphate, Pho90 assumes an asymmetric structure with one monomer facing inward and one monomer facing outward, providing insights into the transport mechanism. The Pho90 transport domain binds phosphate ions on one side of the membrane, then flips to the other side where the substrate is released. Together with functional experiments, these complementary structures illustrate the transport mechanism of eukaryotic low-affinity phosphate transporters.

Phosphate Transporter BnaPT37 Regulates Phosphate Homeostasis in Brassica napus by Changing Its Translocation and Distribution In Vivo.

Inorganic phosphate (Pi) is actively taken up by Pi transporters (PTs) from the soil and transported into the plant. Here, we functionally characterized the Brassica napus gene BnaPT37, which belongs to the PHT1 family. BnaPT37 is a plasma membrane-localized protein containing 534 amino acids. Expression of BnaPT37 increased significantly under Pi deficiency in various tissues, especially in fully expanded leaves. Expression of the ß-glucuronidase reporter gene driven by the BnaPT37 promoter showed that BnaPT37 is expressed in the root, stem, calyx, and leaf under Pi deficiency. BnaPT37 can complement a yeast mutant strain defective in five Pi transporters and can restore the growth of the Arabidopsis atpt1/2 double mutant under Pi deprivation. Overexpression of BnaPT37 in rapeseed significantly increased Pi translocation from root to shoot. Moreover, the movement of Pi from fully expanded leaves to new leaves and roots was enhanced in the transgenic lines compared to the wild type. However, the overexpression of BnaPT37 inhibited the flowering time, plant height, and Pi accumulation in seeds. In conclusion, BnaPT37 functions as a plasma membrane-localized Pi transporter and might be involved in Pi translocation from root to shoot and Pi distribution from source to sink in B. napus.

Phosphate transporters OsPHT1;9 and OsPHT1;10 are involved in phosphate uptake in rice.

We characterized the function of two rice phosphate (Pi) transporters: OsPHT1;9 (OsPT9) and OsPHT1;10 (OsPT10). OsPT9 and OsPT10 were expressed in the root epidermis, root hairs and lateral roots, with their expression being specifically induced by Pi starvation. In leaves, expression of the two genes was observed in both mesophyll and vasculature. High-affinity Km values for Pi transport of OsPT9 and OsPT10 were determined by yeast experiments and two-electrode voltage clamp analysis of anion transport in Xenopus oocytes expressing OsPT9 and OsPT10. Pi uptake and Pi concentrations in transgenic plants harbouring overexpressed OsPT9 and OsPT10 were determined by Pi concentration analysis and (33) P-labelled Pi uptake rate analysis. Significantly higher Pi uptake rates in transgenic plants compared with wild-type plants were observed under both high-Pi and low-Pi solution culture conditions. Conversely, although no alterations in Pi concentration were found in OsPT9 or OsPT10 knockdown plants, a significant reduction in Pi concentration in both shoots and roots was observed in double-knockdown plants grown under both high- and low-Pi conditions. Taken together, our results suggest that OsPT9 and OsPT10 redundantly function in Pi uptake.