Superior yield and phosphorus (P)-use efficiency closely coupled with leaf P remobilization and grain P allocation in an elite rice line under low P availability.

Rice germplasm with high phosphorus (P)-use efficiency for grain production (PUEg) and superior yield under reduced P-fertilizer input is important for sustainable agriculture. However, elite resources with high PUEg and the underlying physiological and molecular traits associated with their superior performance are not well characterized. This study identified an elite rice germplasm with superior PUEg and grain yield under low P availability, and characterized its photosynthetic parameters, leaf P fractions and allocation, transcript expression of acid phosphatase (ACP) and P transporters. Among 36 rice lines, R527 was identified as a P-efficient line, exhibiting 1.34-fold higher PUEg, 1.74-fold higher partial factor productivity of applied P, and 34% higher yield than IR58025 under low P availability. R527 maintained faster net photosynthetic rates and higher photosynthetic PUE while maintaining a similar leaf P concentration to IR58025. R527 exhibited significantly higher ACP activity and expression of OsACP1 and OsACP2. These changes were associated with greater hydrolysis of lipid P and residual P. R527 upregulated P-transporter genes (OsPHT1;8, OsPHO1;1, OsPHT1;7, SPDT, OsPHO1;2) in node I. This was accompanied by enhanced grain P allocation under low P availability. We conclude that the superior productivity and higher PUEg of R527 under low P availability are closely coupled with a coordinated synergy of enhanced leaf P remobilization and efficient nodal P transport to grain. This study provides both valuable germplasm and novel insights for breeding P-efficient rice varieties with superior yield under reduced P fertilizer application.