Epigallocatechin-3-Gallate (EGCG): A unique secondary metabolite with diverse roles in plant-environment interaction

Catechins are a group of secondary metabolites ubiquitously found in tea plants. Epigallocatechin-3-Gallate (EGCG) is the major kind of catechin synthesized through the specific branches of the flavonoid biosynthesis pathway. Catechin synthesis is sensitive to environmental perturbations such as shading, high temperature, cold, drought, salinity, heavy metal stress and biotic attacks, and there has been a close relationship between catechin accumulation and plant stress tolerance. Moreover, exogenous catechin application promotes photosynthesis, plant growth, leaf development, antioxidant defense, reactive oxygen species signaling, redox homeostasis and hormone metabolism under perturbed environmental conditions. Although low concentrations of catechins exert hormetic effects, growth promotion response and stress tolerance, high concentrations of catechins induce phytotoxicity. In this article, we review the biological functions of catechins, especially EGCG from the plant perspective. We describe the effects of various stresses on catechin metabolism in plants, mainly in tea plants, and the possible biological roles that they play in plant adaptation to variable environments. We also discuss the effects of exogenous catechins on plants other than the tea plant with respect to plant growth response and adaptation to variable environments. We conclude that despite discrepancies in research findings, it is evident that catechins play a critical role in plant environmental adaptability and immune response. Thus we propose that the hormetic growth response, stress modulatory effect and immune priming properties of catechins can be exploited for enhancing crop production in an environmentally friendly manner.