Auxin Biosynthesis Is Required for Phosphorus Deficiency‐Induced Root Architecture Remodelling in Rice

Phosphorus (P) deficiency severely restricts plant growth due to its low mobility in soil, driving the evolution of adaptive root system architecture (RSA) remodelling. While auxin has been implicated in P deficiency responses, the molecular mechanisms governing RSA plasticity in rice (Oryza sativa) remain unclear. Here, we identify LRLP1/OsTAR2 and OsYUC8 as key regulators of P-dependent RSA modifications through auxin biosynthesis. The lrlp1 mutant, exhibiting impaired lateral root (LR) and root hair (RH) development under low P, harbors a loss-of-function mutation in OsTAR2, a tryptophan aminotransferase essential for indole-3-pyruvic acid (IPyA)-dependent auxin production. Similarly, CRISPR-Cas9 knockout of OsYUC8, a downstream flavin monooxygenase in the auxin pathway, attenuated LR and RH responses to P stress. Spatial analysis using DR5::VENUS revealed P-deficiency-enhanced auxin signaling in root tips, LR primordia, and epidermal cells. Both lrlp1 and yuc8 mutants showed diminished IAA concentration responses compared to WT under both P conditions. Transcriptomic profiling demonstrated that both mutants exhibit blunted induction of P-starvation response (PSR) genes and auxin signaling genes, including phosphate transporters (OsPHT1s), phosphate signaling components (OsSPXs), and Auxin Response Factors (OsARFs), linking auxin biosynthesis and signaling to PSR regulation. Our work uncovers a conserved yet diversified auxin biosynthesis module that shapes RSA plasticity under P stress, with OsTAR2 adopting a broader regulatory role than its Arabidopsis homologs and downstream gene OsYUC8 in rice. These findings provide actionable targets for breeding P-efficient rice through precision engineering of auxin-mediated root adaptations.