OsPHR2 activates OsPAP23 to promote organic phosphorus utilization in rice

To adapt to low-phosphate environments, plants have evolved elaborate response mechanisms. Among these, the transcription factor OsPHR2 functions as a central regulator of the phosphate (Pi) signaling network, orchestrating the expression of a series of Pi starvation responsive genes. In this study, by integrating ChIP-seq and transcriptomic data, we identified a novel direct downstream target gene of OsPHR2, OsPAP23, which encodes a purple acid phosphatase. Experimental validation confirmed that OsPHR2 activates the transcription of OsPAP23 by binding to the P1BS element in its promoter. OsPAP23 is primarily localized to the endoplasmic reticulum and its coding gene is expressed in various tissues including root epidermis, stems, and panicles. Overexpression of OsPAP23 significantly increases inorganic phosphate concentration, but not total phosphorus concentration, in rice leaves, and enhances total and root-secreted acid phosphatase activity. Additionally, OsPAP23 exhibits high in vitro hydrolytic activity toward phytate (InsP₆). Genetic analysis assay showed that overexpression of OsPAP23 reversed the Pi deficient phenotype in phr2. Furthermore, OsPAP23 overexpression lines showed better growth performance under culture conditions where organic phosphorus serves as the sole phosphorus source. Overexpression of OsPAP23 accelerates the remobilization of seed-stored phytate into Pi and promotes seed germination in rice. In conclusion, this study uncovers the important role of the OsPHR2-OsPAP23 regulatory module in mediating organic phosphorus mobilization and phosphorus homeostasis in rice, providing a new target for breeding crops with high phosphorus-use efficiency.