RNA interference-mediated silencing of the key flavonoid and isoflavone biosynthesis enzyme, respectively, by two different research groups has provided direct genetic evidence for the essential roles that these compounds play in nodulation. Anton Wasson et al. have shown that flavonoids are essential for localized auxin transport inhibition during nodulation in the indeterminate legume Medicago truncatula. By contrast, Senthil Subramanian et al. have shown that isoflavones are essential for endogenous nod gene induction in the determinate legume soybean.