LysM-Type Mycorrhizal Receptor Recruited for Rhizobium Symbiosis in Nonlegume Parasponia

Rhizobium root nodule symbiosis is generally considered to be unique for legumes. However, there is one exception and that is Parasponia . In this nonlegume, the rhizobial nodule symbiosis evolved independently and is, like in legumes, induced by rhizobium Nod factors. We used Parasponia to identify genetic constrains underlying evolution of Nod factor signalling. Part of the signalling cascade, downstream of Nod factor perception, has been recruited from the more ancient arbuscular endomycorrhizal symbiosis. However, legume Nod factor receptors that activate this common signalling pathway are not essential for arbuscular endomycorrhizae. Here, we show that in Parasponia a single Nod factor-like receptor is indispensable for both symbiotic interactions. Therefore we conclude that also the Nod factor perception mechanism is recruited from the widespread endomycorrhizal symbiosis.