A type 5 acid phosphatase gene from Arabidopsis thaliana is induced by phosphate starvation and by some other types of phosphate mobilising/oxidativestress conditions

Low phosphorous availability, a common condition of many soils, is known to stimulate phosphatase activity in plants; however, the molecular details o f this response remain mostly unknown. We purified and sequenced the N-term inal region of a phosphate starvation induced acid phosphatase (AtACP5) fro m Arabidopsis thaliana, and cloned its cDNA and the corresponding genomic D NA. The nucleotide sequence of the cDNA predicted that AtACP5 is synthesise d as a 338 amino acid-long precursor with a signal peptide. AtACP5 was foun d to be related to known purple acid phosphatases, especially to mammal typ e 5 acid pnospnarases. Other similarities with purple acid phosphatases, wh ich contain a dinuclear metal centre, include the conservation of all resid ues involved in metal ligand binding and resistance to tartrate inhibition. In addition, AtACP5, like other type 5 acid phosphatases, displayed peroxi dation activity. Northern hybridisation experiments, as well as in sifu glu curonidase (GUS) activity assays on transgenic plants harbouring AtACP5:GUS translational fusions, showed that AtACP5 is not only responsive to phosph ate starvation but also to ABA and salt stress. It is also expressed in sen escent leaves and during oxidative stress induced by H202r but not by paraq uat or salicylic acid. Given its bifunctionality, as it displays both phosp hatase and peroxidation activity, we propose that AtACP5 could be involved in phosphate mobilisation and in the metabolism of reactive oxygen species in stressed or senescent parts of the plant.