This NSF-funded project uses functional genomics to investigate the process of legume root hair infection by nitrogen-fixing rhizobia. This infection initiates the symbiosis between this bacterium and its host that will result in the de novo formation of a novel organ, the nodule. It is within the nodule that the bacterium fixes nitrogen providing its host plant an advantage in environments where this element is limiting. The establishment of the symbiosis involves a complex interplay between host and symbiont, which is orchestrated by the exchange of diffusible signal molecules.