Synthetic microbial community-assisted regulation of arsenic transport and metabolism reduces grain arsenic accumulation in rice across developmental stages.

Arsenic contamination in paddy soils threatens crop productivity and results in the accumulation of toxic arsenic in rice grains. Here, we demonstrate that a defined synthetic microbial community (SynCom) of Priestia flexa and Pseudomonas putida mitigates arsenic toxicity and restricts arsenic accumulation in rice (Oryza sativa var. Sarju-52). Under arsenic stress [As(III), 18 mg/kg; As(V), 50 mg/kg], plants exhibited impaired growth, reduced photosynthetic performance, and increased oxidative stress. Inoculation with SynCom restored physiological function and metabolic balance, as evidenced by improved photosynthesis, increased soluble sugars, and reduced proline accumulation. Accompanied by attenuation of antioxidant enzyme overactivation, which indicates effective control of reactive oxygen species. Mechanistically, SynCom substantially reduced arsenic accumulation in roots, shoots and grains by coordinate downregulation of arsenic transporter genes (Lsi1, Lsi2, Lsi3, OsNIP1;1, and OsNIP3;3), which limits arsenic uptake and translocation. Metabolomic profiling also indicated stress-associated metabolite suppression and enrichment of growth-related pathways. These results demonstrate that microbiome engineering can reprogram plant responses to arsenic stress and provide a scalable strategy to reduce dietary arsenic exposure from staple crops. Additionally, this study lays a strong foundation for developing SynCom as an effective and sustainable biotechnological intervention to improve food safety and agricultural resilience in arsenic-contaminated areas.