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

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.