Receptor-mediated chitin perception in legume roots is functionally separable from Nod factor perception

Significance Like 80–90% of land plants, legumes form endosymbioses with arbuscular mycorrhizal fungi, host endophytes, support a rhizosphere community, and are attacked by pathogens. The ability of root cells to distinguish between these soil microbes and the mixture of chitinaceous compounds they display as signal molecules is important for an appropriate plant response. We show that legumes possess very similar receptors enabling root cells to separate perception of chitin, which triggers responses to pathogens, from perception of lipochitin oligosaccharides (Nod factors), which trigger endosymbiosis with rhizobial bacteria. The chitin receptors bind chitin in biochemical assays, and inactivation of the corresponding genes impairs defense responses toward pathogens. Together this establishes a long-sought foundation for dissecting plants’ response mechanisms toward different soil microbes.