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GrainGenes Reference Report: PMB-53-27

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Reference	PMB-53-27
Title	Characterization of two phosphate transporters from barley; evidence for diverse function and kinetic properties among members of the Pht1 family
Journal	Plant Molecular Biology
Year	2003
Volume	53
Pages	27-36
Author	Rae AL Cybinski DH Jarmey JM Smith FW
Abstract	Summary: Putative phosphate transporters have been identified in a barley (Hordeum vulgare L.) genomic library by their homology to known phosphate transporters from dicot species. The genes designated HORvu;Pht1;1 and HORvu;Pht1;6 encode proteins of 521 and 535 amino acids respectively with 12 predicted membrane-spanning domains and other motifs common to the Pht1 family of phosphate transporters. HORvu;Pht1;1 is expressed exclusively in roots and is strongly induced by phosphate deprivation. HORvu;Pht1;6 is expressed in the aerial parts of the plant with strongest expression in old leaves and flag leaves. In situ hybridization showed that HORvu;Pht1;6 is expressed in the phloem of vascular bundles in leaves and ears. In order to study the biochemical properties of HORvu;Pht1;1 and HORvu;Pht1;6, the genes were expressed in transgenic rice (Oryza sativa L.) plants under the control of the rice actin promoter and suspension cell cultures were generated. Cells derived from transgenic plants were able to take up phosphate at a much higher rate than control cells, demonstrating that both genes encode functional phosphate transporters. The estimated Km for phosphate for cells expressing HORvu;Pht1;1 was 9.06(+/-)0.82 micromolar, which is characteristic of a high-affinity transporter. The rate of phosphate uptake decreased with increasing pH, suggesting that HORvu;Pht1;1 operates as a H+/H2PO4- symporter. In contrast, the estimated Km for phosphate for cells expressing HORvu;Pht1;6 was 385(+/-) 61 micromolar, which is characteristic of a low-affinity transporter. Taken together, the results suggest that HORvu;Pht1;1 functions in uptake of phosphate at the root surface, while HORvu;Pht1;6 probably functions in remobilization of stored phosphate from leaves
Keyword	[ Hide all but 1 of 37 ] amino arabidopsis thaliana barley cell cloning domain family gene genomic libraries homology hordeum hordeum vulgare hybridization in situ in situ hybridization ion transport kinetic properties mechanism member mineral nutrition oryza oryza sativa oryza sativum ph phloem phosphate phosphate transport phosphate uptake phosphorus promoter redistribution remobilization rice transgenic transgenic rice transporters vascular bundles

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