The microRNA399-PHOSPHATE2 module acts as a dual regulator of root architecture and systemic signaling under phosphate starvation in rice

The microRNA399-PHOSPHATE2 ( miR399-PHO2 ) module is known to maintain phosphate homeostasis in plants, yet its spatiotemporal control and integration of phosphate signaling under low-phosphate (LP) stress remain unclear. In this study, we show that LP induces distinct OsmiR399/OsPHO2 expression dynamics in roots versus shoots, and root-derived OsmiR399 preferentially suppresses OsPHO2 to facilitate P uptake and translocation. An OsmiR399 -resistant OsPHO2-b mutant with deletion of OsmiR399 -binding sites within OsPHO2 5′-UTR, significantly reduces shoot P overaccumulation in OsPHR2/OsmiR399 overexpressors under P-replete conditions. Under LP stress, both OsPHO2-b and osmir399 mutants display reduced root plasticity, enhanced shoot growth inhibition and accelerated leaf senescence. Transcriptomic and cellular analyses revealed tissue-specific dysregulation of P-starvation response (PSR) genes, with suppressed expression in roots but elevated in shoots, as well as defective root-shoot P redistribution. Root-split experiments further showed that OsPHO2-b disrupts systemic auxin signaling and root elongation response to local LP stimuli. Genetic evidence revealed that OsPHO2 functionally intersects with OsNLA1 to synergistically regulate PSRs in a P-dependent manner. Meanwhile, overexpression of OsPHO1-2 significantly enhances root elongation and P translocation in OsPHO2-b . Collectively, our findings establish the OsmiR399-OsPHO2 module as a central hub for root-shoot communication, coordinating root plasticity with systemic signaling to facilitate LP acclimation in rice.