Peptide Binding By Alloproteins and Mutants of a Receptor Like Kinase in Soybean

The protein encoded by GmRLK18-1 (Glyma_18_02680 on chromosome 18) and GmRLK11-1 were nearly identical, syntenic, receptor like kinases (RLK)  encoded within and outside the soybean (Glycine max L. Merr.) Rhg1/Rfs2 locus respectively. The locus underlies resistance to the soybean cyst nematode (SCN) Heterodera glycines (I.) and causal agent of sudden death syndrome (SDS) Fusarium virguliforme (Aoki). The aims here were to localize the RLKs; and evaluate 4 mutant alloproteins LRRs ability to;  homo-dimerize; bind larger proteins; and bind to small peptides. In planta proteins were localized to the pericycle by immunohistochemistry. The purified LRR domain, from residue 131-485, was seen to form a mixture of monomers and homo-dimers in vitro. Cross-linking experiments in vitro showed the H274N,Q and V region was close (<11.1 A) to the highly conserved cysteine residue C196 on the second homo-dimer subunit. Binding constants of 20-142 nM for peptides found in plant and nematode secretions were depended on peptide and mutant sequences. A LRR from GmRLK08-1 (Glyma_08_g11350) did not show these strong interactions. The LRR domain bound avidly to 4 different CLE peptides, a cyclophilin and a methionine synthase in a sequence dependent fashion. The CLE peptides GmTGIF and HgCLE were shown to alter stem morphology and resistance to SCN and SDS.  Therefore, the LRR domains of GmRLK18-1 and GmRLK11-1 might underlie both root development and disease resistance in soybean and provide an avenue to develop new variants and ligands that might promote reduced losses to SCN and SDS.