Metal transport in Medicago truncatula nodule rhizobia-infected cells

Symbiotic nitrogen fixation requires relatively large quantities of essential transition metals (iron, copper, zinc, etc.) as essential cofactors of many of the enzymes involved in this process. These nutrients are delivered by the host plant, in a complex process that requires soluble metal‐binding molecules and dedicated metal transporters. In the last years, the metal transporters responsible for iron, copper, zinc, and molybdate uptake by rhizobia‐infected cells in Medicago truncatula nodules have been identified, and the role that metal binding molecules such as citrate and nicotianamine play in symbiotic nitrogen fixation is gaining more attention. In this chapter, we will present the recent advances in this field and discuss the aspects of nodule transition metal homeostasis that still need addressing.