A GmNRF5a-GmCERK1-GmCAK1 module mediates chitin/chitosan-triggered immune response in soybean

Chitin and its deacetylated derivative chitosan are the major components of fungal cell walls and are recognized by plant pattern-recognition receptors (PRRs) as pathogen-associated molecular patterns that induce innate immunity. Recognition of chitin oligosaccharide (CTOS) in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) requires the membrane-localized lysin-motif (LysM)-domain-containing receptors AtLYK5 and OsCEBiP, respectively. However, the mechanism underlying chitosan oligosaccharide (CSOS)-induced plant immunity remains unclear. In this study, we determined that CTOS and CSOS trigger immune responses and boost disease resistance in soybean (Glycine max) through the LysM-domain-containing protein GmNRF5a and its co-receptor GmCERK1. Surprisingly, both GmNFR5a and GmCERK1 bind directly to CTOS and CSOS, with distinct binding sites. The receptor-like kinase GmCAK1 acts downstream of GmCERK1 and is essential for CTOS/CSOS-mediated immune activation. Overall, these findings uncovered how soybean plants respond to CSOS and initiate immune signaling, demonstrating that soybean exploits shared immune sectors to transduce immune signals triggered by CTOS/CSOS, paving the way for the development of disease-resistant crops with broad-spectrum resistance.