In Mediterranean area, legumes occupy an important place due to their agro-economic and environmental interests. These plants contribute to the nitrogen incorporation in ecosystems by nitrogen fixation symbiosis (NFS) involving rhizobial strains. This association provides the necessary nitrogen for plant growth and contributes to the improvement of the soil nitrogen balance to the benefit of other crops in intercropping systems or in rotation. Consequently, the rhizobial symbiosis could, through the cultivation of legumes, allow farmers to save the chemical fertilizer costs and alleviate their environment pollution effects. However, the environmental constraints, such as water deficit and low soil phosphorus availability, prevailing in Mediterranean region, affect negatively the SNF performance and causing thus a decrease in grain and forage legume yields. In this context, our present project aims at exploration of legume-rhizobia functioning diversity to select and characterize tolerant symbiosis to water deficit under limiting phosphorus conditions. The works will focus on physiological, biochemical and molecular tools at plant and rhizobia levels.