Large-scale multi-omics unveils host–microbiome interactions driving root development and nitrogen acquisition

The rhizosphere microbiome plays a crucial role in determining plant performance and fitness. Nevertheless, regulatory mechanisms linking host genetic variation, root gene regulation and microbiome assembly-and their collective influence on plant nutritional traits-remain poorly understood. Here we generated and integrated 1,341 paired datasets, including root transcriptomes, rhizosphere bacterial 16S rRNA profiles and root ionomes, across 175 resequenced Brassica napus ecotypes grown at two contrasting field sites. We identified 203 highly heritable bacterial amplicon sequence variants (ASVs), many of which were significantly associated with root nitrogen (N) levels. Host transcriptome-wide gene expression and these microbial features together explained up to 45% of natural variation in N uptake while genome-wide association analyses revealed host loci regulating ASV abundance, many of which were under the control of eQTL hotspots linked to carbon and N metabolism. Isolate-level inoculation, whole-genome sequencing, metabolite profiling and confocal imaging demonstrated that the dominant, genetically regulated bacterial genus Sphingopyxis modulates auxin biosynthesis and promotes lateral root development to enhance N acquisition under stress. This study therefore identifies Sphingopyxis as a functionally relevant taxon with potential for microbiome-assisted breeding of nutrient-efficient crops.