Comparative Transcriptomic Analysis Reveals Regulatory Mechanisms of Theanine Synthesis in Tea (Camellia sinensis) and Oil Tea (Camellia oleifera) Plants

Tea provides a rich taste and has healthy properties due to its variety of bioactive compounds, such as theanine, catechins, and caffeine. Theanine is the most abundant free amino acid (40%-70%) in tea leaves. Key genes related to theanine biosynthesis have been studied, but relatively little is known about the regulatory mechanisms of theanine accumulation in tea leaves. Herein, we analyzed theanine content in tea (Camellia sinensis) and oil tea (Camellia oleifera) and found it to be higher in the roots than in other tissues in both species. The theanine content was significantly higher in tea than oil tea. To explore the regulatory mechanisms of theanine accumulation, we identified genes involved in theanine biosynthesis by RNA-Seq analysis and compared theanine-related modules. Moreover, we cloned theanine synthase (TS) promoters from tea and oil tea plants and found that a difference in TS expression and cis-acting elements may explain the difference in theanine accumulation between the two species. These data provide an important resource for regulatory mechanisms of theanine accumulation in tea plants.