Nissolia brasiliensis as a nonnodulating model legume.
The nitrogen-fixing root nodule symbiosis is specifically formed by 4 orders of angiosperms. The largest of these 4 orders includes the legume family, the Fabaceae. Among legumes, historical model species have emerged, such as the root nodule symbiosis-forming Medicago truncatula and Lotus japonicus or, more recently, Aeschynomene evenia. By contrast, legume species that have lost root nodule symbiosis have been largely ignored. Here, we describe the first near chromosome-level assembly for a non-root nodule symbiosis-forming legume, the tropical Papilionoideae Nissolia brasiliensis. We compared its genome to closely related legumes and identified genes associated with root nodule symbiosis. Finally, we developed a stable transformation protocol that can be deployed in the future to reevolve root nodule symbiosis in legumes, a first step toward the goal of engineering root nodule symbiosis in nonlegume crops.