HEFEI -- Tea, one of the world's most popular beverages, owes its unique flavor to theanine, an amino acid. Theanine provides a delicate sweetness that balances the bitterness of catechins and caffeine, while its calming effects can ease anxiety and promote better sleep.

Theanine levels are high in new tea plant shoots that arise during early spring, but then significantly decrease in late spring, causing a rapid decline in the quality of green tea processed from the late-spring harvest.

However, the molecular mechanisms underlying this seasonal decrease in theanine levels remained unknown for years. Recently, a team led by Professor Zhang Zhaoliang of Anhui Agricultural University has solved the puzzle through long-term study, with findings published in the journal The Plant Cell.

During spring's rapid growth phase, tea plants metabolize theanine as a nitrogen source for new shoot development. First, the CsTHS1 transporter delivers theanine from the cytoplasm to mitochondria -- the "powerhouse" of the cell. Then, the CsGGT2 enzyme degrades theanine, lowering its concentration.

Temperature is a key regulator of this process. With seasonal warming, both CsTHS1 and CsGGT2 increase in tea plants, accelerating theanine degradation.

By revealing theanine metabolism in tea plants, this study may provide strategies to improve late-spring tea flavor. "We can use gene editing for precision breeding, or develop special fertilizers and shading techniques to maintain theanine levels for smarter cultivation of premium spring teas," Zhang said.