Understanding how arbuscular mycorrhizal (AM) symbioses establish and function is one of the most important current challenges in microbial ecology. Despite the fact that the AM symbiosis requires some complex and fine molecular tuning among symbionts in order to take place, both partners benefit from each other in a number of ways. For instance, the availability, uptake and exchange of nutrients in this biotrophic interaction are key factors driving plant growth and modulating biomass allocation. This underground trade is regulated by both plant and fungal transport components [1], as for instance the long distance transport of photosynthates from leaves towards colonized roots and the subsequent reciprocal transfer of nutrients from the soil to the plant through the fungal partner. More than a trophic role, it appears that nutrients themselves, acting as signals, function as major regulators of mycorrhizal associations [2]. The establishment and functioning of plant-fungal trophic interface as well as the local adaptation of fungal mycelium rely on complex and highly coordinated plant and fungal transcriptome regulations that are not well understood. Here, we focus in particular on key players involved in the nutritional exchanges between the mycorrhizal plant and the associated AM fungi. A better understanding of the underground trade will be useful for developing future engineering of new agro-ecological systems.