An aeroponic system to characterize maize root exudates in relation to N and P nutrition and arbuscular mycorrhizal symbiosis

Root exudates play major roles in the recruitment of plant microbiota. The metabolic composition of root exudates varies according to plant developmental stage, nutrient availability, (a)biotic stresses, and interaction with the root-associated microbiota, including arbuscular mycorrhizal fungi (AMF), which play a key role in plant mineral nutrition and stress tolerance. While it is well established that AMF can perceive plant root exudate compounds, little is known about plant root exudate modifications in response to AMF inoculation. Here, we developed an aeroponic-based culture system suitable for the analysis of maize root exudates during symbiosis with the AMF Rhizophagus irregularis while controlling nutrient availability. We validated the functionality of the system by monitoring both maize root colonization by the AMF and the expression profile of symbiotic root marker genes. We then investigated the composition of root exudates (strigolactones and other specialized metabolites) from mycorrhizal and non-mycorrhizal plants grown under different nitrogen and phosphorus regimes. Comparisons of specialized metabolite profiles from root exudates, root tissues, and fungal extracts allowed us to identify candidate metabolic features specifically accumulating in mycorrhizal root exudates. Thus, we provide an innovative method to better understand the role of root exudate metabolites in shaping the microbiota of mycorrhizal plants.