Root-derived brassinosteroids coordinate high rice yield and methane mitigation under wetting alternating with mild drying management

• Wetting alternating with mild drying (WMD) synergistically achieves high rice yield and mitigates CH 4 emissions. • The WMD approach increases the level of root-derived brassinosteroids in rice. • Root-derived brassinosteroids optimize critical processes at the rice root-soil interface. This study explored the effects of a wetting alternating with mild drying (WMD) management strategy, on rice productivity and methane (CH 4 ) emissions, and its underlying mechanisms. A high-yielding hybrid rice cultivar was grown in field trials under either conventional irrigation (CI) or the WMD regimen from transplanting to maturity. Results revealed that the WMD approach significantly boosted grain yield while simultaneously reducing CH 4 emissions. It was accompanied by a slight increase in nitrous oxide (N 2 O) emissions versus CI. However, the mitigation benefits of decreased CH 4 emissions in lowering global warming potential (GWP) and greenhouse-gas intensity (GHGI) outweighed the adverse contributions of elevated N 2 O emissions. Elevated BR levels in roots enhanced antioxidant defense through the ascorbate-glutathione cycle pathway, which reduced ROS accumulation, thereby not only maintaining root activity but also suppressing root aerenchyma formation—ultimately restricting CH 4 transport pathways under WMD regime. Furthermore, the increased root BR levels suppressed CH 4 production by directly or indirectly inhibiting the mcrA gene abundance, while promoting CH 4 oxidation through rhizosphere exudates enriched with specific organic acids that stimulated the pmoA gene abundance in paddy soil. Under the WMD regime, BR-induced enhancement of root activity significantly boosted photosynthetic capacity, establishing a positive feedback loop that promoted assimilate accumulation. Concurrently, WMD facilitated photosynthate allocation from vegetative tissues to grains, collectively improving rice yield. Collectively, our data suggest that the WMD practices can effectively reduce CH 4 emissions, GWP, and GHGI in rice paddies while maintaining high grain yield by stimulating root-derived BR biosynthesis.