Final Report Summary - MENOMED (Metal homeostasis in nodulated Medicago truncatula)
Towards this goal we have determined the path that metals follow from soil to reach the nodule. This has been achieved using synchrotron-based X-ray fluorescence in collaboration with researchers at Argonne National Laboratory (USA). Our results indicate that iron, and likely other transition metals, are released from the vasculature into the apoplast of the infection/differentiation zone of the nodule.
This would ensure a maximum availability of the essential metal oligonutrients at the same time and place as the apoproteins involved in nitrogen fixation are being synthesized. To determine the transporters involved in metal uptake and delivery to the symbiosome, we have used a transcriptomic approach identifying ten genes involved in metal homeostasis upregulated more than seven fold in the nodule, some of them nodule-specific. Several of these transporters, such as MtNramp1, are located in the plasma membrane of cells in the infection/differentiation zone of the nodule.
Consequently with their putative importance in symbiotic nitrogen fixation, mutation of these transporters result in loss of nitrogen fixation capabilities due to essential metal cofactors not reaching their designated target apoproteins. All these results open a new venue to improve nitrogen fixation capabilities in legumes by optimizing metal delivery to the nodules.