Molecular genetics of the symbiosis of forage legumes and nitrogen fixing bacteria

OM AGUILAR

Ciudad Autonoma de Buenos Aires

Simposio; 6th International Symposium on the Molecular Breeding of Forage and Turf; 2010

Under conditions of nitrogen limitations, soil bacteria of the genera Rhizobium, Bradyrhizobium, Sinorhizobium, Mesorhizobium, and Azorhizobium, generically named rhizobia, enter into a symbiosis with certain legume plants that results in the formation of root nodules. In optimal growth conditions, this association provides enough fixed nitrogen to the plant, which represents an alternative fertilization independent of non-renewable resources. Our limited understanding of symbiosis –at the molecular level- was derived mainly from investigations on the model legumes Medicago truncatula and Lotus japonicus. Upon stimulation by flavonoids exuded from legume roots into the soil, rhizobia synthesize signaling molecules that are responsible for nodule formation. These signalling molecules have been identified as lipochitin oligosaccharides (LCOs), and are sufficient to activate the plant cell cycle machinery for cortical cell divisions. Progresses in the identification of members of this process led to propose a signal transduction pathway triggered by the nodulation factor. In this presentation, the basic mechanism of legume-rhizobia interaction involved in the legume early response to rhizobial infection will be shown. In addition, novel genes discovered in the grain legume Phaseolus vulgaris other than those participating in the Nod factor induced pathway will be discussed.