Arabidopsis Purple Acid Phosphatase with Phytase Activity Increases Foliar Ascorbate

• Published in: Plant physiology (Bethesda) 2008-02, Vol.146 (2), p.431-440
• Main Authors: Zhang, Wenyan, Gruszewski, Hope A, Chevone, Boris I, Nessler, Craig L
• Format: Article
• Language: English
• Subjects: Acid Phosphatase - genetics; Acid Phosphatase - metabolism; Amino Acid Sequence; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Ascorbic Acid - biosynthesis; Biochemical Processes and Macromolecular Structures; Biological and medical sciences; Biosynthesis; Cauliflower mosaic virus; Enzymes; Fundamental and applied biological sciences. Psychology; Gene expression regulation; Gene Expression Regulation, Plant - physiology; Genes. Genome; Glycoproteins - genetics; Glycoproteins - metabolism; Inositols; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; Multienzyme Complexes - genetics; Multienzyme Complexes - metabolism; Ozone; Phosphatases; Phosphates; Phytic Acid - metabolism; Plant Leaves - metabolism; Plant roots; Plants; Yeasts
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.107.109934

Ascorbate (AsA) is the most abundant antioxidant in plant cells and a cofactor for a large number of key enzymes. However, the mechanism of how AsA levels are regulated in plant cells remains unknown. The Arabidopsis (Arabidopsis thaliana) activation-tagged mutant AT23040 showed a pleiotropic phenotype, including ozone resistance, rapid growth, and leaves containing higher AsA than wild-type plants. The phenotype was caused by activation of a purple acid phosphatase (PAP) gene, AtPAP15, which contains a dinuclear metal center in the active site. AtPAP15 was universally expressed in all tested organs in wild-type plants. Overexpression of AtPAP15 with the 35S cauliflower mosaic virus promoter produced mutants with up to 2-fold increased foliar AsA, 20% to 30% decrease in foliar phytate, enhanced salt tolerance, and decreased abscisic acid sensitivity. Two independent SALK T-DNA insertion mutants in AtPAP15 had 30% less foliar AsA and 15% to 20% more phytate than wild-type plants and decreased tolerance to abiotic stresses. Enzyme activity of partially purified AtPAP15 from plant crude extract and recombinant AtPAP15 expressed in bacteria and yeast was highest when phytate was used as substrate, indicating that AtPAP15 is a phytase. Recombinant AtPAP15 also showed enzyme activity on the substrate myoinositol-1-phosphate, indicating that the AtPAP15 is a phytase that hydrolyzes myoinositol hexakisphosphate to yield myoinositol and free phosphate. Myoinositol is a known precursor for AsA biosynthesis in plants. Thus, AtPAP15 may modulate AsA levels by controlling the input of myoinositol into this branch of AsA biosynthesis in Arabidopsis.