GmNFR1 of Two Non-nodulation Mutants

Gene duplication in evolution has long been viewed as a mechanism for functional divergence. We recently cloned two related lipo-oligochitin receptor genes (GmNFR1α and GmNFR1β) in Glycine max (soybean) that allowed the distinction of two nodulation factor (NF) responses during early legume nodule ontogeny, namely invasion of the root hair and concomitant cortical cell divisions. Root-controlled GmNFR1α mutants nod49 and rj1 failed to form curled root hairs, infection threads and nodules but develop subepidermal cortical cell divisions (CCD) and mycorrhizal associations. In contrast GmNFR1β mutant PI437.654 had full symbiotic abilities. However, GmNFR1α mutants formed normal nodules at reduced frequency when inoculated with high Bradyrhizobium titers. The mutation was complemented in Agrobacterium rhizogenes K599 transformed roots using both CaMV 35S and the native GmNFR1α promoters. GmNFR1α may encode a high affinity NF receptor responsible for the entire nodulation cascade while GmNFR1β with lower affinity to NF suffices to induce cell divisions but not early infection events.