Untangling the rhizosphere specialized metabolome

The importance of microbes in helping plants deal with unfavorable environmental conditions is currently receiving a lot of attention. Still, how plants and microbes communicate on a chemical level warrants a deeper understanding. Both plants and microbes exude specialized metabolites (SMs) into the rhizosphere, and the exudate profiles drastically change under sub-optimal conditions such as drought. Yet, it remains unclear what the ecophysiological functions of these exuded compounds are and whether common underlying patterns exist across different plant species. The complexity of chemical mixtures in the rhizosphere, the diversity of microbial communities, and dissimilar experimental conditions are impeding progress in this field. With this article, we aim to link plant-derived SMs under normal and stressful conditions to their signaling effect on soil microbial communities and vice versa while pointing out the newest developments and bottlenecks of getting to the function of root exudate composition. Additionally, we provide some best practices for increasing comparability and reproducibility among experiments.