LysM Receptor-Like Kinase LYK9 of L. May Regulate Plant Responses to Chitooligosaccharides Differing in Structure.

This study focused on the interactions of pea ( L.) plants with phytopathogenic and beneficial fungi. Here, we examined whether the lysin-motif (LysM) receptor-like kinase LYK9 is directly involved in the perception of long- and short-chain chitooligosaccharides (COs) released after hydrolysis of the cell walls of phytopathogenic fungi and identified in arbuscular mycorrhizal (AM) fungal exudates. The identification and analysis of pea mutants impaired in the gene confirmed the involvement of LYK9 in symbiosis development with AM fungi. Additionally, LYK9 regulated the immune response and resistance to phytopathogenic fungi, suggesting its bifunctional role. The existence of co-receptors may provide explanations for the potential dual role of LYK9 in the regulation of interactions with pathogenic and AM fungi. Co-immunoprecipitation assay revealed that LYK9 and two proposed co-receptors, LYR4 and LYR3, can form complexes. Analysis of binding capacity showed that LYK9 and LYR4, synthesized as extracellular domains in insect cells, were able to bind the deacetylated (DA) oligomers CO5-DA-CO8-DA. Our results suggest that the receptor complex consisting of LYK9 and LYR4 can trigger a signal pathway that stimulates the immune response in peas. However, LYR3 seems not to be involved in the perception of CO4-5, as a possible co-receptor of LYK9.