Roles of flavonoids in symbiotic and defense functions in legume roots

The roles of flavonoids in roots of legumes in the symbiotic relationships with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi are compared with defense functions, using examples from three legume genera,Lotus, Medicago, andGlycine. Pathways leading to proanthocyanidins and isoflavonoids are emphasized. The localization of flavonoids in nodules involved in nitrogen fixation and in the apoplastic compartment of mycorrhizal associations is briefly described, with emphasis on the need for more information concerning their precise localization. Also emphasized are the limits of our knowledge about the regulatory genes of the flavonoid pathway involved in both exogenous and endogenous regulation of these complex interrelationships.