Characterization of Arabidopsis acid phosphatase promoter and regulation of acid phosphatase expression

The expression and secretion of acid phosphatase (APase) was investigated i n Indian mustard (Brassica juncea L. Czern.) plants using sensitive in vitr o and activity gel assays. Phosphorus (P) starvation induced two APases in Indian mustard roots, only one of which was secreted. Northern-blot analysi s indicated transcriptional regulation of APase expression. Polymerase chai n reaction and Southern-blot analyses revealed two APase homologs in Indian mustard, whereas in Arabidopsis, only one APase homolog was detected. The Arabidopsis APase promoter region was cloned and fused to the beta -glucuro nidase (GUS) and green fluorescent protein (GFP) reporter genes. GUS expres sion was first evident in leaves of the P-starved Arabidopsis plants. In P- starved roots, the expression of GUS initiated in lateral root meristems fo llowed by generalized expression throughout the root. GUS expression dimini shed with the addition of P to the medium. Expression of GFP in P-starved r oots also initiated in the lateral root meristems and the recombinant GFP w ith the APase signal peptide was secreted by the roots into the medium. The APase promoter was specifically activated by low P levels. The removal of other essential elements or the addition of salicylic or jasmonic acids, kn own inducers of gene expression, did not activate the APase promoter. This novel APase promoter may be used as a plant-inducible gene expression syste m for the production of recombinant proteins and as a tool to study P metab olism in plants.