O-methylated catechins in tea plant (Camellia sinensis): From biological activities and content influencers to biosynthesis and regulatory mechanisms

In tea plants, O -methylated catechins, which are methylated derivatives of catechins, are characterized by their unique physiological properties, efficient functional activities, specific accumulation and distribution patterns, different synthesis and regulation mechanism that differs from that of catechins and flavonoids. Presently, there have been identified at least 14 O -methylated catechins, with EGCG3″Me being the most abundant and extensively studied in tea plants. However, a comprehensive review on the current state of research on O -methylated catechins is currently lacking. This review summarizes the progress and current status of the research on O -methylated catechins. More specifically, the biological activities and functions, endogenous and exogenous influencing factors, biosynthesis and transcription regulation of O -methylated catechins are systematically described. Moreover, the future research directions of O -methylated catechins are discussed. The information presented herein may help to fill the knowledge gap regarding O -methylated derivatives of catechins in tea plants, while also providing guidance for future in-depth research, development, and use of O -methylated catechins.