The Burholderia pyrrocinia Purple Acid Phosphatase Pap9 Mediates Phosphate Acquisition in Plants

Increasing the expression level of purple acid phosphatases (PAPs), which hydrolyze organic phosphate to inorganic phosphate (Pi), is an important response to Pi starvation in plants. PAPs are widely distributed in eukaryotes like mammals and plants but distributed in limited microorganisms. A PAP-like protein named Pap9 from Burkholderia pyrrocinia CH-67 was isolated. The enzyme had optimal activity at atypical pH of 8.5 and temperature of 85°C. When pap9 was overexpressed in Arabidopsis thaliana, the APase activity in the transgenic plants was about 15% to 40% higher under acidic conditions and had an approximately four-fold increase under alkaline conditions compared with wild type. Overexpression of pap9 in plants enhanced APase activity under Pi-deficient conditions more than under Pi-sufficient conditions. In-gel assays revealed that Pap9 exists as a monomer in transgenic plants. Root surface-associated APase activity in transgenic plants increased dramatically during acidic and Pi-deficient conditions. These results indicated that bacterial Pap9 in transgenic plants was secreted onto the root surface and released into the rhizosphere. The transgenic plants have significantly enhanced biomass that have the potential for use in biotechnological applications.