The Dual‐Barrier Mechanism of Gibberellin in Alleviating Aluminium Toxicity: Cell Wall Immobilization and Casparian Strip Reinforcement

Aluminium (Al) toxicity severely limits crop productivity in acidic soils by inhibiting root growth and nutrient uptake, yet the hormonal mechanisms coordinating Al defence in tobacco remain unclear. Here, we show that Al stress rapidly induces gibberellin (GA) biosynthesis in tobacco roots, and that GA signalling mitigates Al toxicity by promoting root growth and reducing Al accumulation. Using exogenous GA application, CRISPR/Cas9-mediated NtGA3-ox1 mutants, GA biosynthesis inhibitors, transcriptomic profiling, and biochemical analyses, we demonstrate that GA enhances Al exclusion through two complementary mechanisms: remodelling root cell wall composition, particularly by increasing hemicellulose content to sequester Al, and reinforcing the endodermal Casparian strip (CS) through the upregulation of CS-associated genes. Pharmacological manipulation of lignin biosynthesis confirms that early CS formation was critical for restricting Al entry. These findings reveal GA as a dynamic regulator of Al stress adaptation, coordinating structural and biochemical defences to maintain root growth, and highlight GA signalling as a potential target for improving crop tolerance to Al-toxic acidic soils.