Overexpression of OsPAP10a, A Root-Associated Acid Phosphatase, Increased Extracellular Organic Phosphorus Utilization in Rice

Phosphorus (P) deficiency is a major limitation for plant growth and development. Among the wide set of responses to cope with low soil P, plants increase their level of intracellular and secreted acid phosphatases (APases), which helps to catalyze inorganic phosphate (Pi) hydrolysis from organo-phosphates. In this study we characterized the rice (Oryza sativa) purple acid phosphatase 10a (OsPAP10a). OsPAP10a belongs to group Ia of purple acid phosphatases (PAPs), and clusters with the principal secreted PAPs in a variety of plant species including Arabidopsis. The transcript abundance of OsPAP10a is specifically induced by Pi deficiency and is controlled by OsPHR2, the central transcription factor controlling Pi homeostasis. In gel activity assays of root and shoot protein extracts, it was revealed that OsPAP10a is a major acid phosphatase isoform induced by Pi starvation. Constitutive overexpression of OsPAP10a results in a significant increase of phosphatase activity in both shoot and root protein extracts. In vivo root 5-bromo-4-chloro-3-indolyl-phosphate (BCIP) assays and activity measurements on external media showed that OsPAP10a is a root-associated APase. Furthermore, overexpression of OsPAP10a significantly improved ATP hydrolysis and utilization compared with wild type plants. These results indicate that OsPAP10a can potentially be used for crop breeding to improve the efficiency of P use.