Molecular cloning and characterization of a tobacco leaf cDNA encoding a phosphate transporter

Phosphate acquired by roots is translocated to and utilized by the upper pa rt of the plant, where the phosphate transport in the cell is also importan t in the phosphate metabolism. Tn order to study the role of the phosphate transporter in the regulation of the phosphate movement across the membrane s in leaf cells, we isolated and characterized a 2,059 bp tobacco leaf cDNA clone, NtPT1. The 537 amino acid sequences, deduced from NtPT1, exhibited 93 and 91% identites to one of the high affinity phosphate transporters con stitutively expressed in potato and tomato roots, respectively. The NtPT1 c ontains 12 membrane-spanning domain with a central hydrophilic region. The expression of NtPT1 in the yeast high affinity phosphate transporter mutant strain, NS219, complemented the mutant and promoted cell growth significan tly, These results strongly suggest that NtPT1 encodes a functional phospha te transporter and that one of the high affinity phosphate transporters exp ressed in roots is also expressed in leaves. Southern analysis indicated th at tobacco phosphate transporter genes are low copy number genes and member s of a small multi-gene family.