Structure of a cDNA for an acid phosphatase from phosphate-deficient lupin (Lupinus albus L.) Roots

Abstract

We have isolated a cDNA clone, named LASAP1, for an acid phosphatase (EC 3.1.3.2; APase) from a cDNA library constructed from mRNA in phosphatedeficient lupin (Lupinus albus L. cv. Kievskij) roots. LASAP1 was 2,187 bp in length including a single open reading frame of 1,914 nucleotides that encodes 638 amino acid residues containing a putative signal sequence of 31 amino acids. The polypeptide encoded by LASAP1 was highly hydrophilic, while the putative signal peptide was highly hydrophobic. It was predicted that the peptide had a high affinity to the plasma membrane. The deduced amino acid sequence shared a high homology with that of purple APases from germinated seeds of Phaseolus vulgaris and those secreted from Arabidopsis thaliana. Seven amino acids composing the active center of the Phaseolus vulgaris purple APase were conserved in all the homologous APases. Northern blot analysis revealed that the corresponding mRNA accumulated in both shoots and roots under phosphate deficient conditions, and that the amount of transcript in the roots was much larger than that in the shoots. These results suggest that APase encoded by LASAP1 cDNA is expressed predominantly in the roots.

Key Words:

• acid phosphatase (APase)
• lupin
• phosphate deficiency
• secretion