From Phytoalexins to Environmental Regulators: An Evolving Understanding of the Role of Coumarins in Regulating Quorum Sensing and Shaping the Soil Microbiome

Quorum sensing (QS) governs microbial virulence, symbiosis, and critical ecosystem processes, such as rhizosphere nitrogen mineralization, positioning QS as both an attractive agricultural target and a potential point of ecological trade-off. This review synthesizes current evidence on coumarins, plant-derived secondary metabolites, that have evolved from being viewed as classical phytoalexins to being recognized as regulators of QS-mediated interaction in the plant-soil system. We synthesize current evidence on the multifaceted mechanisms of coumarin action, from direct antimicrobial effects to selective interference with bacterial QS systems and virulence. Key studies demonstrate that coumarins can suppress phytopathogens while sparing beneficial bacteria, thereby actively editing rhizosphere community composition. However, coumarin effects are profoundly context-dependent, with outcomes ranging from selective microbiome modulation to broad suppression or unintended pathogen enrichment - depending on concentration, plant host and native community structure. Beyond community assembly, coumarin-mediated QS disruption may have functional consequences for QS controlled ecosystem processes such as nutrient cycling. Revealing a potential ecological trade-off between pathogen defense and resource acquisition, this warrants further investigation. Coumarins are versatile compounds that plants use for sensing, communicating with, and actively shaping their microbial environments. Developing the ability to use them precisely and in an environmentally friendly manner represents a promising avenue for sustainable agriculture.