Duplicated Nod-Factor receptor 5 (NFR5) genes are mutated in soybean

In symbiosis with Bradyrhizobium japonicum, soybean (Glycine max L.) forms nitrogen-fixing nodules in its roots after mitogenic stimulation from a bacterial lipo-oligosaccharide (the 'Nod-factor'). In our recent paper in Plant and Cell Physiology we utilize two recessive loss-of-function plant mutants with a non-nodulation phenotype, and comparative genomics to clone and functionally analyze relevant soybean genes of the LysM receptor kinase family which are needed for perception of Nod-factor released by its microsymbiont B. japonicum. Two highly related lipo-oligochitin LysM type receptor kinase genes were cloned; they are presumed to be the critical nodulation inducing (Nod) factor receptor. These duplicated receptor genes were called GmNFR5α and GmNFR5β. Non-sense mutations in GmNFR5α and GmNFR5β were functionally complemented by both wild-type GmNFR5α and GmNFR5β in transgenic roots, indicating that both genes are functional. Both genes are wild-type in some soybean cultivars; however, non-functional NFR5β alleles were discovered in several others, which harbored an identical 1,407 bp retroelement-type insertion. GmNFR5α but not GmNFR5β was expressed in tap and lateral root portions at about 10-25% of GmATS1 (ATP synthase subunit 1), but not in trifoliate leaves and shoot tips. In general, inoculation treatment down-regulated GmNFR5α/β transcripts in tap and lateral root portions.