Signalling in symbiotic root nodule formation

Rhizobia form nodules on legume roots in which they carry out biological nitrogen fixation. The location and number of nodules is tightly regulated. Exchange of signal molecules that activate responses in the symbiotic partner takes place: plant flavonoids induce the production of rhizobial Nod factors; Nod factors induce gene expression and morphogenesis in the legume root. ENOD40 is a plant gene induced by Nod factors that is involved in root nodule formation. ENOD40 encodes a peptide of 12 amino acids in soya bean that can induce tolerance of high auxin concentrations in tobacco protoplasts.