Legumes are widely-consumed plants that use soil bacteria to obtain nitrogen through root nodulation. The process is energetically costly, and so legumes inhibit nodulation when soil nitrate is available. However, the mechanism that drives this inhibition is unknown. Researchers found that NRSYM1 is responsible for inhibiting nodulation in the presence of nitrate, and acts by directly regulating gene expression. The findings may aid agricultural efforts to improve the crop efficiency of legumes.