Root Exudates as Key Regulators of Plant–Microbe Interactions

Root exudates — the diverse array of organic and inorganic compounds released by plant roots into the surrounding soil — are increasingly recognised as central orchestrators of the plant–microbiome dialogue in the rhizosphere. Far from representing merely metabolic waste products, these secretions function as precise chemical signals that selectively recruit, suppress, or tolerate soil-dwelling microorganisms, thereby shaping the composition and activity of the rhizosphere microbiome with remarkable specificity. This review synthesises current knowledge on the chemical classification of root exudates, the mechanisms governing their secretion, and their roles in mediating symbiotic associations with arbuscular mycorrhizal fungi and rhizobia, supporting plant growth-promoting rhizobacteria, driving disease suppression, and modulating plant immunity. It also examines how abiotic stresses alter exudate profiles, how microbial communities feed back to reshape root metabolism, and the methodological advances that are enabling increasingly detailed characterisation of the rhizosphere metabolome. The literature search underpinning this review was conducted across the following databases: Web of Science, Scopus, PubMed, Google Scholar, and the USDA National Agricultural Library's Agricola database. Finally, the review considers the agricultural and biotechnological implications of harnessing root exudate chemistry, including possibilities for engineering rhizosphere microbiomes to improve nutrient use efficiency, stress tolerance, and crop productivity. Despite significant progress, substantial gaps remain in understanding the spatial dynamics of exudate gradients, the functional consequences of exudate diversity across plant genotypes, and the translation of laboratory findings to field conditions. Addressing these challenges will be essential to realise the full potential of root exudate biology in sustainable agriculture.