Coumarin Communication Along the Microbiome–Root–Shoot Axis

Plants shape their rhizosphere microbiome by secreting root exudates into the soil environment. Recently, root-exuded coumarins were identified as novel players in plant–microbiome communication. Beneficial members of the root-associated microbiome stimulate coumarin biosynthesis in roots and their excretion into the rhizosphere. The iron-mobilizing activity of coumarins facilitates iron uptake from the soil environment, while their selective antimicrobial activity shapes the root microbiome, resulting in promotion of plant growth and health. Evidence is accumulating that, in analogy to strigolactones and flavonoids, coumarins may act in microbiome-to-root-to-shoot signaling events. Here, we review this multifaceted role of coumarins in bidirectional chemical communication along the microbiome–root–shoot axis. Bidirectional signaling occurs along the microbiome–root–shoot axis in plants much akin to that along the human microbiome–gut–brain axis.Production of plant secondary metabolites elicited by rhizosphere microbiota, such as coumarins, can directly impact the composition and activity of the microbial community.Microbially elicited production of secondary metabolites in the roots can act as intertissue messengers in plants.Coumarins are the ‘new kids on the block’ in the chemical communication along the microbiome–root–shoot axis.