Redefining Root Exudation with Proteins at the Forefront of Rhizosphere Function

Root exudates are vital mediators of rhizosphere interactions, yet existing studies have primarily emphasized primary and secondary metabolites while neglecting root-exuded proteins. Increasing evidence indicates that root-exuded proteins play critical roles in nutrient acquisition, microbial recruitment, and plant defense. These proteins, including proteases, phosphatases, and chitinases, facilitate the mobilization of organic nitrogen and phosphorus, often bypassing the need for microbial intermediaries. Additionally, pathogenesis-related proteins, β-1,3-glucanases, and ribosome-inactivating proteins contribute to the suppression of pathogens and the activation of the immune system. Root-exuded proteins also function as signaling molecules, modulating rhizosphere microbial communities under biotic and abiotic stress. Recent advances have uncovered both classical (ER-Golgi) and unconventional secretion mechanisms, including exocyst-positive organelles and multivesicular bodies. Despite these developments, challenges in extraction, functional validation, and in situ analysis remain. Emerging technologies, such as stable isotope labeling, biosensors, and multiomics integration, offer promising solutions. Root-exuded proteins thus represent an underexplored frontier in rhizosphere ecology, with substantial potential for sustainable agriculture and rhizosphere engineering.