Legumes are the second major food source for humans and livestock, and crucial elements in any sustainable strategy of agriculture, since they are the main responsible of fixed nitrogen in natural ecosystems, and the largest supplier of nitrogen for agriculture. This is due to the establishment in their roots of a symbiotic relationship with rhizobia. In it, the rhizobia colonize a new organ, the nodule. In this organ, a microaerobiotic environment is essential for nitrogenase, the key enzyme of nitrogen fixation, to work. In exchange for fixed nitrogen, the plant provides the rhizobia with fixed carbon and oligonutrients such as iron and copper. Iron and copper play an essential role in the nodule, being involved in nitrogenase enzymatic activity, creation of the microaerobiotic environment, protection against free radical species created as side product of nitrogen fixation, energy obtention, and in producing regulatory free radicals, among other processes. However, essential heavy metals are scarce nutrients in soils, and are a frequent limiting crop yields. Therefore, we hypothesize that the host legume must strive to satisfy the nodule´s demand for more metals, and consequently mobilize these precious nutrients from other parts of the plant. As a consequence, the legume must alter the expression levels of metal homeostasis genes, change the distribution of metal along the plant, express new metal transporters in the nodule, and recover the metals once the nodule senesced. We will test this hypothesis by studying the:

i) metal transcriptome in the nodulated plant,

ii) metallome in the nodulated plant,

iii) functional characterization (biochemical and physiological) of Cu and Fe transporters expressed in the nodule. For this, we will use as a model plant Medicago truncatula, and state of the art technology, such as the new Affymetrix chips or X-ray fluorescence to determine metal distribution.