LAUSR

Understanding the composition and activation of multicomponent receptor complexes is a challenge in biology. To address this, we developed a synthetic approach based on nanobodies to drive assembly and activation of cell surface receptors and apply the concept by manipulating receptors that govern plant symbiosis with nitrogen-fixing bacteria. We show that the Lotus japonicus Nod factor receptors NFR1 and NFR5 constitute the core receptor complex initiating the cortical root nodule organogenesis program as well as the epidermal program controlling infection. We find that organogenesis signaling is mediated by the intracellular kinase domains whereas infection requires functional ectodomains. Finally, we identify evolutionarily distant barley receptors that activate root nodule organogenesis, which could enable engineering of biological nitrogen-fixation into cereals. Description Parsing nodulation pathways Legumes benefit from symbiotic microbes resident in root nodules that fix nitrogen, whereas most other plants depend on externally supplied or gathered nitrogen. Rübsam et al. identified a bifunctional receptor complex in the model legume Lotus japonicus that initiates development and infection of the root nodules. Development of root nodules could be driven solely by the intracellular domains containing the kinases once the receptor complex was formed, but the Nod factor–recognizing ectodomains were required to support rhizobial infection. Receptors identified in the cereal barley, which does not form symbiotic nitrogen-fixing root nodules, were able to support Lotus root nodule organogenesis, suggesting that the path to nitrogen fixation in cereals might be shorter than we thought. —PJH Llama nanobodies help identify the receptor complex that controls nodule organogenesis in plant symbiosis with nitrogen-fixing bacteria.