BRADYRHIZOBIUM-ELKANII LIPO-OLIGOSACCHARIDE SIGNALS INDUCE COMPLETE NODULE STRUCTURES ON GLYCINE-SOJA SIEBOLD ET ZUCC

The (Brady)rhizobium nodulation gene products synthesize lipo-oligosac charide (LOS) signal molecules that induce nodule primordia on legume roots. Previously, nodule primordia had been induced by LOS on several legumes, but the induction of a complete nodule structure by LOS had only been shown on alfalfa. Since alfalfa can spontaneously form nodul es at a low frequency, it has been unclear whether LOS molecules are s ufficient to induce morphologically complete nodules on plants that do not spontaneously form nodules. In this study, we isolated LOS from B radyrhizobium elkanii previously Bradyrhizobium japonicum group II; Ku ykendall et al. 1992, Can. J. Microbiol. 38, 501-505) strain USDA61 an d determined their biological activity on Glycine soja. When spot-inoc ulated onto G. soja roots, these LOS induced a morphologically complet e nodule structure showing many features similar to root nodules induc ed by rhizobia. These features include a broad mitotically active nodu le primordium in the root outer cortex and a vascular bundle that eman ates from the pericycle and bifurcates to surround the mitotically act ive cells. From this work it can be concluded that LOS are sufficient to induce a structurally complete nodule on plants that form determina te nodules.