Theanine constitutes nearly half of all free amino acids in tea leaves and largely defines the beverage's umami flavor and soothing properties. Synthesized mainly in the roots and transported to young shoots, theanine's levels are tightly linked to nitrogen metabolism and environmental cues such as temperature and light. Transcription factors, particularly WRKY proteins, are known to control multiple metabolic pathways, including amino acid and secondary metabolite biosynthesis. Yet, how phytohormones like gibberellin influence theanine production through transcriptional regulation has remained largely unknown. Due to these unresolved questions, researchers sought to uncover how gibberellin signaling affects the molecular control of theanine synthesis in tea plants.
A research team from the Tea Research Institute of the Hunan Academy of Agricultural Science and Hunan Agricultural University, China, reported new findings (DOI: 10.1093/hr/uhae317) on February 1, 2025, in Horticulture Research. Their study demonstrated that gibberellin (GA₃) enhances the expression of CsTSI, the major gene responsible for theanine biosynthesis, by downregulating CsWRKY71, a nuclear transcription factor that directly binds to and represses the CsTSI promoter. This discovery provides the first molecular evidence linking gibberellin signaling to theanine accumulation in tea plants.
Using hydroponically grown seedlings of the tea cultivar “Baojing Huangjincha 1,” researchers observed that external application of gibberellin (1 μmol L⁻¹ GA₃) significantly increased CsTSI expression and theanine content in roots, stems, and leaves within 48 hours. Molecular assays—including promoter analysis, yeast one-hybrid, electrophoretic mobility shift (EMSA), and dual-luciferase reporter assays—confirmed that CsWRKY71 binds to the CsTSI promoter's W-box element ((C/T)TGAC(T/C)) to suppress gene expression. When gibberellin was applied, CsWRKY71 expression decreased markedly, lifting its inhibition and allowing CsTSI to drive theanine synthesis. The team also verified that CsWRKY71 localizes to the nucleus and functions as a transcriptional repressor. Transient suppression of CsWRKY71 in tea shoots via antisense oligonucleotide (asODN) further elevated CsTSI expression and theanine levels. Collectively, these findings reveal a clear regulatory cascade in which gibberellin suppresses CsWRKY71, thereby enhancing CsTSI expression and promoting theanine biosynthesis. A proposed model summarizes this mechanism, establishing a new framework for hormone-mediated quality regulation in tea.
“Our study uncovers how gibberellin regulates a key flavor compound in tea through a transcriptional switch,” said corresponding author Prof. Wei Li. “We identified CsWRKY71 as a negative regulator of CsTSI, and showed that gibberellin relieves this repression to stimulate theanine accumulation. This not only explains a long-observed link between growth hormones and tea taste, but also highlights a targetable molecular pathway for breeding or cultivation strategies aimed at enhancing tea quality.”
This discovery provides a molecular explanation for how environmental and hormonal cues shape tea flavor quality. Understanding the GA₃–CsWRKY71–CsTSI regulatory axis offers valuable insights for optimizing the balance between growth and flavor in tea cultivation. Controlled application of gibberellin could help farmers increase both yield and theanine content, while molecular breeding could focus on downregulating CsWRKY71 to develop naturally high-theanine varieties. Beyond tea, the findings shed light on how phytohormones modulate nitrogen-derived metabolites, offering broader implications for improving flavor and nutritional quality in other crops.
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References
DOI
10.1093/hr/uhae317
Original Source URL
https://doi.org/10.1093/hr/uhae317
Funding information
This work was supported by grants from the National Key R&D Program of China (2022YFD1600801), the Natural Science Foundation of Hunan Province (2023JJ30317, 2024JJ5215), the Natural Science Foundation of Changsha (kq2208086), and the Hunan Innovative Province Construction Project (2021NK1020).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.