Transcriptome and metabolome analysis support that nitrate primarily promotes N and C metabolism in soybean roots and reduces those in nodules.

To dissect differences in gene expression profile of soybean roots and root nodules, we have employed microarray analysis. Seeds of soybean (Glycine max L. cv. Nourin No. 2) were inoculated with rhizobia (Bradyrhizobium diazoefficiens USDA110) and were hydroponically cultivated under controlled conditions with nitrogen free culture solution (Saito et al. 2014). At 19 days after planting, each plant were treated with or without 5 mM nitrate for 24 hours. Roots and nodules from three plants were pooled with three biological replications, and total RNA was extracted. Gene expressions in soybean roots and nodules inoculated with Bradyrhizobium diazoefficiens were analyzed after 24 hours of 5 mM nitrate treatment compared with control with N free medium. Three independent experiments were performed at each inoculation.