Purple Acid Phosphatase Gene <i>PpPAP17a</i> Confers Phosphate Starvation Tolerance in <i>Pennisetum purpureum</i> by Mediating Organic Phosphate Utilization

Inefficient inorganic phosphate (Pi) fertilizer use exacerbates phosphorus resource depletion and environmental pollution. Purple acid phosphatases (PAPs) are crucial for plant adaptation to a Pi deficiency. In elephant grass (<i>Pennisetum purpureum</i>), 50 <i>PpPAP</i> genes were identified and classified into 13 low-molecular-weight (LMW) and 37 high-molecular-weight members. Transcriptomic analysis and RT-qPCR validation revealed that 17 <i>PpPAPs</i> responded to Pi starvation, notably the tandem-duplicated LMW gene <i>PpPAP17a</i>. This gene, which is uniquely conserved in elephant grass, was strongly upregulated in Pi-deficient roots. Yeast one-hybrid and dual-luciferase assays confirmed that its expression was directly activated by the phosphate starvation response regulators PpPHR20 and PpPHR34. Enzymatic assays showed that PpPAP17a efficiently hydrolyzes ATP and localizes to the plasma membrane and nucleus. Functionally, overexpressing <i>PpPAP17a</i> in rice enhanced acid phosphatase activity, increased phosphorus content, improved root growth and photosynthesis, and ultimately improved grain yield under low-Pi conditions. Thus, <i>PpPAP17a</i> represents a key candidate for developing Pi-efficient crops.