Bacterial modification of the root cell wall facilitates rice aluminum resistance in acidic soils

The root cell wall is a pivotal microbial interface for crop stress resilience in adverse soils. While rhizosphere microorganisms influence root development through nutrient exchange and hormonal signaling, their role in remodeling the cell wall under aluminum toxicity in acidic soils remains unknown. Here, we demonstrate that a synthetic microbial community (SynCom) enhances root tolerance to aluminum in rice by activating xyloglucan endotransglucosylase activity. This response reduces aluminum-binding sites within cell-wall xyloglucans, thereby decreasing aluminum accumulation by 47.5% in the root apoplast. SynCom promotes brassinosteroid biosynthesis through the mevalonate pathway. Multi-omics analyses and genetic evidence from xyloglucan endotransglucosylase- and brassinosteroid-deficient mutants reveal that SynCom serves as a metabolic contributor, supplying brassinosteroid precursors to the root apex. This microbial regulation establishes hormonal homeostasis and directs cell-wall remodeling to alleviate aluminum toxicity. Our findings propose a microbially enhanced strategy to improve crop resilience in acidic soils by reinforcing root stress adaptation.