FeSYM · Cytosolic Iron Delivery for Symbiotic Nitrogen Fixation

Symbiotic nitrogen fixation (SNF) carried out by legume nodules is one of the most efficient ways of introducing nitrogen in natural ecosystems and in sustainable agriculture. It relies on the transfer of a relatively large amount of iron from the host plant to the endosymbiotic bacteria colonizing nodule cells, where it will be used as cofactor of many of the enzymes participating in SNF. However, the required steady iron supply for SNF is challenged by its low bioavailability in soil, prevalent in many of the main agricultural areas of the world. This is worsened by the hundreds of ferro-enzymes that compete for iron cofactors within a cell. Due to the relevance of SNF for a more sustainable agriculture, and the importance of ensuring iron supply to achieve this, a substantial effort has been done in understanding how legumes incorporate iron and deliver it to the nodules, and how it is used to synthesize nitrogenase cofactors. However, no information is available on how iron is specifically allocated to the nitrogen-fixing compartments. In this proposal we intend to study the mechanisms enabling targeted iron delivery to nitrogen fixation, particularly those events occurring at the cytosol and at the interface between the two symbionts. To do this, we will identify and characterize the proteins interacting the known symbiosome iron transporters. As a result, we will characterize the iron-interactome of these elements. These findings should not only increase our understanding of iron homeostasis in SNF and, more broadly, in plants, but also lead to dedicated iron delivery pathways for iron-biofortification or to engineer iron-proteins in plants.