OsPHR2‐OsDIR55 Module Enhances Root Barrier Integrity and Rice Tolerance to Phosphate Deficiency

ABSTRACT Low bioavailability of inorganic phosphate (P i ) in soil severely constrains plant growth and crop productivity. Here, we demonstrate that P i deficiency induced localised lignification in rice roots. Overexpression of OsDIR55 , a beneficial gene we previously implicated in salt tolerance, significantly enhances plant performance under low P i conditions, characterised by increased root‐to‐shoot ratio and biomass accumulation, whereas loss‐of‐function dir55 mutants exhibit contrast phenotypes. Importantly, the transcription factor OsPHR2 physically binds to the P1BS cis ‐elements in the OsDIR55 promoter, and P i deprivation upregulates OsDIR55 expression in an OsPHR2‐dependent manner. We further showed that OsDIR55 maintains cellular P i homoeostasis under P i starvation by reinforcing root apoplastic barrier functionality. Disruption of OsDIR55 leads to excessive P i accumulation and aberrant physiological responses under P i ‐sufficient conditions with leaf tip necrosis, indicative of P i toxicity. Our work uncovers an essential role of the OsPHR2‐OsDIR55 module in mediating root anatomical adaptations to P i scarcity, refines P i stress signalling pathways and highlights the significance of lignification in plant responses to environmental stresses.