Carotenoid biosynthesis drives root plasticity through aerenchyma and iron plaque formation in rice.

Rice roots develop aerenchyma, which transports oxygen from shoots to roots, facilitating adaptation to waterlogged conditions. This oxygen oxidizes ferrous ions into ferric compounds, forming iron plaque that mitigates iron toxicity. However, the molecular mechanisms linking aerenchyma and iron plaque formation remain poorly understood. Here we identified a rice mutant (AZ1302) defective in both aerenchyma and iron plaque formation, with the causal mutation mapped to the PHYTOENE SYNTHASE 2 (OsPSY2) gene. CRISPR-Cas9-induced psy2 mutants exhibited reduced levels of carotenoid-derived hormones, strigolactones and abscisic acid, in roots. In psy2 mutants, exogenous application of strigolactones rescued aerenchyma formation, while abscisic acid restored iron plaque deposition, providing evidence for distinct hormonal regulatory functions in the two processes. These findings revise the current understanding by dissociating the roles of aerenchyma and iron plaque formation, establishing a role for OsPSY2 in integrating hormonal signalling to drive root plasticity and offering new insights into plant adaptation under environmental stress.