The arbuscular mycorrhizal (AM) symbiosis is a fascinating mutulistic interaction between roots of most land plants and soil fungi. It is so widespread that it majorly influences ecosystem functioning, and is considered of fundamental importance for crop productivity and sustainability. Mutualism is achieved through an exchange of soil minerals for organic carbon at specialised fungal structures, the arbuscules. Arbuscules form inside root cortex cells, surrounded by a plant-derived membrane, the peri-arbuscular membrane (PAM), across which efflux of organic carbon and uptake of minerals occurs. However, arbuscules are ephemeral structures, forming and collapsing in a few days, implying a similarly dynamic nature for the reciprocal nutrient exchange. We used key mineral uptake and carbon efflux transporters residing in the PAM of rice as a proxy for nutrient exchange, and employed advanced non-invasive, live imaging to capture arbuscule formation and turnover in real time. I will introduce our observations which provide a first glimpse on the mechanisms operating at the ‘heart’ of mutualism of this intimate plant-fungal partnership.
