A spatiotemporal single-cell atlas reveals coordinated immune, metabolic, and nutrient exchange programs and a coumarin-centered metabolic switch during soybean arbusular mycorrhizal symbiosis

Arbuscular mycorrhizal fungi (AMF) establish intimate symbiosis with plant roots, yet the cell-type-specific regulatory and metabolic programs governing this interaction remain poorly resolved. Here, we integrate single-nucleus RNA sequencing (snRNA-seq) with spatial metabolomics across a temporal gradient of soybean root colonization (2-8 weeks post inoculation) to construct a high-resolution, multi-omic atlas of AMF symbiosis. Profiling 33,410 nuclei spanning all major root cell types, we uncover dynamic, cell-type-resolved transcriptional reprogramming coupled to spatially localized metabolite accumulation. Early colonization triggers a robust, epidermis-localized immune response alongside cortex-specific epigenetic reprogramming, mediated by RNA-directed DNA methylation machinery, suggesting active suppression of defense in fungal accommodation zones. Spatial metabolomics reveals a biphasic metabolic transition from flavonoid- and terpenoid-rich signaling states to lipid-dominated nutrient exchange, aligned with colonization progression. In parallel, coordinated carbon allocation and lipid biosynthesis pathways were activated in cortex and vascular tissues, supporting fungal dependence on host-derived fatty acids and sugars. Nutrient exchange programs, particularly nitrogen and phosphorus transport, exhibit strong pericycle and phloem specificity, highlighting systemic integration of symbiotic benefits. Through co-expression network analysis, we identify a previously uncharacterized coumarin-centered metabolic switch, governed by GmF6H1-2, that is essential for efficient colonization, as validated by natural loss-of-function variants. Collectively, this study provides a comprehensive, spatially resolved framework linking gene regulation, metabolism, and cell identity, revealing that AMF symbiosis is orchestrated through coordinated immune modulation, metabolic rewiring, and nutrient flux partitioning at single-cell resolution.