Molecular control of acid phosphatase secretion into the rhizosphere of proteoid roots from phosphorus-stressed white lupin

White lupin (Lupinus albus) grown under P deficiency displays a suite of hi ghly coordinated adaptive responses. Included among these is secretion of c opious amounts of acid phosphatase (APase). Although numerous reports docum ent that plants secrete APases in response to P deficiency, little is known of the biochemical and molecular events involved in this process. Here we characterize the secreted APase protein, cDNA, and gene from white lupin. T he secreted APase enzyme is a glycoprotein with broad substrate specificity . It is synthesized as a preprotein with a deduced M-r of 52,000 containing a 31-amino acid presequence. Analysis of the presequence predicts that the protein is targeted to outside the cell. The processed protein has a predi cted M-r of 49,000 but migrates as a protein with M-r of 70,000 on sodium d odecyl sulfate gels. This is likely due to glycosylation. Enhanced expressi on is fairly specific to proteoid roots of P-stressed plants and involves e nhanced synthesis of both enzyme protein and mRNA. Secreted APase appears t o be encoded by a single gene containing seven exons interrupted by six int rons. The 5'-upstream putative promoter of the white lupin-secreted APase c ontains a 50-base pair region having 72% identity to an Arabidopsis APase p romoter that is responsive to P deficiency. The white lupin-secreted APase promoter and targeting sequence may be useful tools for genetically enginee ring important proteins from plant roots.