Plant Phenolics: Role in Biotic Stress Alleviation and Plant Microbe Interactions

Phenolic compounds are structurally and functionally diverse organic compounds synthesized by plants, which apart from being involved in various plant life processes, significantly contribute to plant defense. As plant defense molecules, their production may be induced after the pathogen has attacked the plant or the synthesis may be constitutive. The phenolics act by different modes of action depending on their chemical structure and, nature, and position of the substituent groups. They may disrupt membrane integrity, inhibit enzyme activity, or block energy metabolism in the target pathogenic species. Phenolics provide color and aroma to the fruits. These are the universal signaling molecules at low concentrations, but at higher concentrations, they serve as allelopathic chemicals and antimicrobial phytoalexins. Phenolics are important in the plant–microbe interactions; interaction between leguminous plants and Rhizobium sp. and symbioses between mycorrhiza and the host plant roots require two-way exchange of phenolic signals between the symbiotic partners. Owing to their high antibacterial and antifungal activities, plant phenolics are seen as an eco-friendly alternative to the chemical pesticides.