The secret to tea quality

A new study has unveiled the intricate genetic mechanisms that regulate theanine accumulation in tea plants — a key determinant of tea quality. The implications of this study extend beyond fundamental plant science to practical applications in the tea industry.

Theanine, a unique non-proteinogenic amino acid, is a signature component of tea, shaping its umami taste and influencing its health benefits. The accumulation of theanine in tea leaves is a dynamic process influenced by environmental factors and plant development stages. While past studies have identified key enzymes involved in its biosynthesis and breakdown, the precise transcriptional regulation governing these processes has remained elusive. Given tea’s global economic significance and rising consumer demand for high-quality brews, decoding the genetic control of theanine metabolism is crucial for future tea improvement strategies.

On January 10, 2024, researchers from Anhui Agricultural University published a study in Horticulture Research that sheds new light on the genetic regulation of theanine metabolism in tea plants. This research systematically investigates the roles of specific genes and transcription factors in determining theanine accumulation, offering novel insights into the molecular basis of tea plant biology.

The study focuses on the functional divergence between two key enzymes, CsGGT2 and CsGGT4, and their transcriptional regulator, CsMYB73. Through biochemical assays, the researchers established that CsGGT4 exhibits significantly higher catalytic efficiency for theanine synthesis, whereas CsGGT2 primarily functions as a theanine hydrolase, breaking down theanine. Advanced homology modelling and molecular docking analyses further revealed structural differences between these enzymes, explaining their distinct roles. Notably, CsGGT4 showed a stronger affinity for ethylamine and glutamine, key substrates in theanine biosynthesis.

Further molecular investigations demonstrated that CsMYB73, a nucleus-localised transcription factor, directly binds to the promoters of CsGGT2 and CsGGT4, exerting opposite regulatory effects: it activates CsGGT2 while repressing CsGGT4, ultimately reducing theanine accumulation in tea shoots. The study also observed that sustained high levels of CsMYB73 expression correlated with increased CsGGT2 activity and diminished CsGGT4 function, leading to lower theanine content. These discoveries reveal a sophisticated genetic control mechanism governing theanine metabolism and open up new possibilities for precision breeding in tea cultivation.

Dr Jun Sun, a lead researcher on the project, highlighted the broader impact of these findings: “Our study provides a comprehensive understanding of the transcriptional regulation of theanine metabolism in tea plants. By uncovering the roles of CsMYB73, CsGGT2 and CsGGT4, we are paving the way for genetic interventions that could enhance tea quality, a factor of great economic and cultural importance.”

The implications of this study extend beyond fundamental plant science to practical applications in the tea industry. By modulating the expression of CsMYB73 and its target genes, scientists and breeders could develop tea cultivars with enhanced theanine content, improving both flavour and health benefits. This research not only deepens our understanding of plant metabolic regulation but also offers a sustainable, science-driven approach to advancing tea cultivation and quality enhancement in the future.

Image credit: iStock.com/Vovchyn Taras