MtCOPT1 mediates copper transport to Medicago truncatula nodules

Copper is an essential oligonutrient. Its redox properties allow it to be a suitable cofactor for many proteins, such as cytochromes or superoxide dismutases. Copper is key for Symbiotic Nitrogen Fixation (SNF); For instance, bacteroids contain copper-dependent cytochrome oxidases that provide energy in the microaerobic environment within the nodule. Once copper is in the plant, it is delivered by the vasculature to the apoplast of zone II. From there, a plasma membrane transporter introduces this nutrient into the cell for copper-protein assembly. COPT family transporters mediate high-affinity copper transport towards the cytosol. Therefore, they are good candidates to introduce copper in nodule cells. From the 8 COPT family genes present in M. truncatula genome, MtCOPT1 is the only one induced specifically in nodule. MtCOPT1 can restore Saccharomyces cerevisae ?ctr1 capacity to uptake copper. Inmunolocalization and GUS fusion studies localize MtCOPT1 in the nodule. Moreover, a Tnt-1-derived knockdown mutant line for MtCOPT1 shows decreased nitrogenase activity when compared with the wild-type line. This activity is, at least, partially rescued when a wild-type copy of MtCOPT1 gene is reintroduced. Taken together, all this data suggest an important role of MtCOPT1 copper-mediated transport for SNF