Nicotianamine-enabled iron delivery for nitrogen fixation

he massive use of nitrogen fertilizers in agriculture is responsible of feeding half of the world population. However, they are an important source of greenhouse gasses, one of the main expenses for farmers (unreacheable in many developing countries), and contribute to water eutrophyzation. Symbiotic nitrogen fixation (SNF) carried out by the rhizobia-legume interaction is one of the main alternatives to the overuse of these fertilizers, in a return to more sustainable practices of crop rotation with legumes. This process requires of relatively large amount of transition metals (iron, copper, zinc,…) that work as cofactors of many of the main enzymes participating in SNF. Given the prevalent low bioavailability of these metals in many of the main agricultural areas of the world, the real impact of crop rotation with legumes in soil nitrogen fertilization will depend in ensuring a continous and suficient delivery of essential transition metals. To improve this, we need to identify and manipulate the molecules mediating the delivery of these nutrients.

The CBGP group “Metal homeostasis in plant-microbe interactions”, in collaboration with researchers from Spain (ICA and EEAD), USA (Noble Reseach Institute and WPI), and France (CNRS, EEAD), has shown that a nicotianamine synthase (NAS) gene is essential for nodule functioning in model legume Medicago truncatula. NAS proteins synthesize the non-proteinogenic amino acid nicotianamine, essential for long-distance iron, copper, and zinc trafficking in plants. Here it shown for the first time how a NAS gene participates in symbiotic nitrogen fixation, delivering the iron required. This is illustrated by the
altered distribution of this nutrient in mutant nodules,observed with synchrotron-based X-ray fluorescence. Moreover, the data indicates an important role of nicotianamine in intracellular iron trafficking.