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Principal investigators: Manuel González Guerrero

Associated with: Centro de Biotecnología y Genómica de Plantas (UPM-INIA)

Project Summary:

Many of the enzymes involved in the main plant biological processes (photosynthesis, germination, …) require transition metals (iron, copper, zinc, …) as cofactors. This determines high metal fluxes from root to sink organs (leaves during vegetative growth; fruits during the reproductive stage), that will ensure a continuous supply of these nutrients. Legumes have an additional sink, the root nodules, where many of the proteins involved in symbiotic nitrogen fixation (nitrogenase, leghemoglobin,…) contain metallic cofactors. This causes legumes, in contrast to other plants, and due to the low metal bioavailbility in many soil types, to have to split a scarce limiting nutrient between two sink organs (leaves and nodules). How do legumes control metal supply to simultaneously optimize nitrogen fixation and photosynthesis? Our hypothesis is that this transit is mediated by a subgroup of long distance metal transporters expressed at high levels in roots of inoculated plants and in their nodules, coordinated with other expressed in the shoot that are down-regulated upon nodulation: the former would increase metal delivery to the nodule, while the latter would reduce metal delivery to the shoot. Preliminary data in model legume Medicago truncatula supports this hypothesis. To further study the mechanisms responsible for regulating metal fluxes between the two main sink organs in legumes, we propose:

i) To determine the localization of the expression of selected genes;

ii) to study their role in the development of plants grown with nitrogen fertilizer or in symbiosis with rhizobia; and

iii) to identify the transcription factors regulating their expression, since these proteins would be in the signalling pathway controlling a correct metal distribution. Towards this end, we will use a
multidisciplinary approach that will involve classical plant physiology methods, legume genetic and molecular biology, microscopy methods, and high-energy physics to visualize metals within the cell. These results will contribute to the design and development of varieties with an improved uptake and distribution of essential, limiting nutrients, contributing to potentiate the use of legumes to diminish the use of nitrogen fertilizers. They will also contribute to the efforts of developing nitrogen fixation capabilities in nonlegumes, by providing the required information so that metal cofactors would reach the required organ with a minimal impact on photosynthetic rates.