Plants host in their rhizosphere a remarkable diversity of microorganisms that in return can promote plant growth and health. The microbiota that is systematically associated with a given plant genotype is called the core microbiota. However, the core microbiota has been mostly defined on taxonomic basis, whilst the microbiota recruited by the plant in different environments seems to share greater functional similarity and the concept of core functional microbiota has been proposed accordingly. The purpose of the PhD thesis is to give evidence of the existence of a core functional microbiota. The PhD thesis aims to: (i) assess the impact of different plant genotypes on the rhizosphere functional community through shotgun metagenomics; (ii) compare the genomics of different strains harboring functional genes identified at point (i) isolated from different soils; (iii) assess if these functional communities are beneficial for plant growth and nutrition through the building of Synthetic Communities (SCs); (iv) evaluate how the plant select these microbiota functions in different soils. In order to valuate if different genotypes belonging to a same plant species are able to select a functional core microbiota, the impact of seven Medicago truncatula genotypes on the rhizosphere microbiota was explored during the first year of my PhD thesis. The first results will be presented.