Molecular Cloning and Root Specific Expression of Secretory Acid Phosphatase from Phosphate Deficient Lupin (Lupinus albus L.)

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During the growth of lupin (Lupinus albus L.) plants, a shortage of phosphate induces the secretion of acid phosphatase (APase) from their roots. We have already isolated and characterized the lasap1 cDNA clone for an APase from phosphate-deficient roots. In this paper, we report on an another cDNA clone, designated as lasap2, encoding secretory APase (S-APase) from phosphate-deficient lupin roots. The lasap2 cDNA consisted of 1,541 bp and had an open reading frame composed of 462 amino acid residues with a signal peptide of 34 residues. Several amino acid sequences of purified lupin S-APase were completely contained in the deduced amino acid sequence (LASAP2). The mature LASAP2 was highly hydrophilic, while the signal peptide was highly hydrophobic. The PSORT prediction program indicated that the mature LASAP2 might be secreted from cells. The primary sequence of LASAP2 shared about 70% homology with that of purple APase from germinating seeds of kidney bean as well as LASAP1. RT-PCR and Western blot analyses revealed that the accumulation of mRNAs and the corresponding proteins for S-APase encoded by lasap2 was induced only in roots under phosphate-deficient conditions, while it was assumed that the LASAP1 hydrolyzed phosphate ester compounds which reached the root surfaces or were released from old organs to the apoplastic space.
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