IDENTIFICATION OF THE TRANSPORTER RESPONSIBLE FOR IRON UPTAKE BY NITROGEN-FIXING CELLS IN MODEL LEGUME MEDICAGO TRUNCATULA

Researchers at CBGP publish in Plant Physiology the identification and characterization of an iron transporter localized in model legume Medicago truncatula symbiotic root nodules. Iron is essential at many steps of symbiotic nitrogen fixation, a key process towards diminishing nitrogen fertilizer use in agriculture.

Iron is an essential element for plants that participates in multiple biological processes, such as photosynthesis or germination. Iron is also used in legumes as a cofactor of many of the enzymes involved in the symbiotic nitrogen fixation carried out in root nodules. Nodules are differentiated root organs resulting of the interaction with beneficial soil bacteria, rhizobia, after a complex exchange of chemical signals. Rhizobia colonize the interior of nodule cells where, under the right conditions, they will use plant-provided iron to synthesize enzymes, like nitrogenase, responsible of converting atmospheric nitrogen in nitrogen species that can be used by the rest of organisms. This iron is incorporated from soil, transported through the vessels, and released in the apoplast of the infection zone of the nodules. A study led by CBGP researchers has identified MtNramp1 as the protein responsible for apoplastic iron uptake in the infection zone of the nodule and introducing this element into rhizobia-infected cells. Removing this transporter results in the loss of nitrogen-fixing capabilities by the symbiosis, a consequence of an essential cofactor not being delivered to endophytic rhizobia. This study opens the door to future research to increase nitrogen fixation rates in legumes and potentiate their use in sustainable agriculture, since iron is a low bioavailability growth-limiting element in most soil types. Identifying and characterizing the transporters mediating iron delivery to sink organs (leaves, nodules, and fruits) is a first essential step to potentiate photosynthesis, nitrogen fixation, and increase fruit nutritional value.

MtNramp1 is required for iron uptake by rhizobia-infected Medicago truncatula nodule cells - DOI: 10.1104/pp.114.254672