Abstract

Phosphorus (P) scarcity severely limits crop productivity; yet, mechanisms balancing P allocation between vegetative and reproductive organs remain unclear. Here, we identify OsPH-2 as a phosphate-responsive regulator in rice ( Oryza sativa L.). Under low-P (LP) conditions, OsPHI-2 is transcriptionally repressed by the KNOX family factor OSH1 (KNOX family class 1 homeobox gene of rice), which directly binds its promoter. CRISPR-edited OsPHI-2 knockout lines exhibited enhanced biomass and adaptive root–shoot resource allocation under LP, whereas overexpression lines showed impaired panicle development and reduced grain yield. This repression fine-tunes P partitioning by modulating expression of transporters ( OsPT2 , OsPHO1;2 ) and vacuolar effluxes ( OsVPE1 ), prioritizing reproductive over vegetative sinks. Haplotype analysis indicated that subspecies-specific P remobilization strategies may be associated with OsPHI-2 . Under P deficiency, Indica rice rapidly suppresses OsPHI-2 expression to preferentially remobilize P to panicles, thereby enhancing adaptation to low-P environments. Our study uncovers an OSH1- OsPHI-2 module that coordinates P allocation, providing a genetic target for improving P-use efficiency in rice.