Tea (Camellia sinensis) is the world’s second most consumed beverage after water, prized for its complex flavor and health-promoting compounds. Theanine, found mainly in young leaves and roots, is central to tea’s signature taste and wellness benefits. While nitrogen fertilization’s influence on theanine is well established, phosphate’s role has been murky, with past findings sometimes contradictory. Excessive Pi can subtly shift tea chemistry, lowering desirable amino acids and altering flavor balance. Yet the molecular “wiring” between Pi signals and theanine biosynthesis has remained elusive. Based on these uncertainties, researchers set out to decode how phosphate availability directly shapes the genetic machinery behind theanine production.
In a study (DOI: 10.1093/hr/uhae242) published August 30, 2024, in Horticulture Research, researchers at Guizhou University report the discovery of a phosphate-responsive genetic module that acts like a master dimmer switch for theanine biosynthesis. Through a blend of transcriptomics, biochemical assays, and genetic manipulation, they pinpointed the CsSPX3–CsPHL7–CsGS1/CsTS1 pathway as the key link between Pi fertilization and reduced theanine. The findings not only explain why over-fertilizing with phosphate can dull tea’s flavor, but also open a path for breeding and cultivation strategies that protect the quality consumers cherish.
The team grew tea plants under a range of Pi concentrations and observed a striking pattern: as Pi content in leaves and roots rose, theanine levels dropped sharply, while catechins and caffeine shifted in the opposite direction. Deep RNA sequencing revealed two Pi-responsive genes—CsSPX3 and CsPHL7—whose activity surged under high Pi and moved in lockstep with reduced expression of theanine biosynthetic genes CsTS1 and CsGS1. Protein interaction experiments confirmed that CsSPX3 physically partners with CsPHL7, and that this duo binds directly to the promoters of CsTS1 and CsGS1, silencing their activity. Silencing CsSPX3 or CsPHL7 via virus-induced gene silencing boosted theanine content by up to 2.36-fold, while transient overexpression cut it by more than a third. The results outline a clear inhibitory circuit: in high-Pi conditions, the CsSPX3–CsPHL7 complex clamps down on theanine biosynthesis, leading to flavor loss in the finished tea.
“This is the missing piece connecting phosphate nutrition to tea quality,” said Professor Litang Lu, senior author of the study. “We now understand that CsSPX3 and CsPHL7 form a direct molecular brake on theanine production when phosphate is abundant. By targeting this pathway, we can help farmers fine-tune fertilizer use, safeguard the umami character of tea, and adapt to changing soil nutrient conditions. It’s a step toward precision tea agriculture—where quality and sustainability go hand in hand.”
The discovery of the CsSPX3–CsPHL7–CsGS1/CsTS1 module opens multiple avenues for protecting tea quality. Breeding programs could develop varieties with naturally lower CsSPX3/CsPHL7 activity, maintaining high theanine even under variable Pi supply. On the cultivation side, fertilizer regimes can be adjusted to avoid triggering the molecular brake on theanine biosynthesis. Beyond tea, the mechanism offers clues for managing nutrient–flavor trade-offs in other crops where secondary metabolites define market value. As the tea industry faces pressure to boost yields while preserving sensory excellence, this research provides a genetic and agronomic blueprint for achieving both.
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References
DOI
10.1093/hr/uhae242
Original Source URL
https://doi.org/10.1093/hr/uhae242
Funding information
This research received support from the Guizhou Province Science and Technology Planning Project (Qiankehe Support [2021] General 111), the earmarked fund for GZMARS-Tea, the Guizhou Province High-level Innovative Talents ‘Hundred’ Level Talent Project (Qiankehe Platform Talent) GCC[2023]014, and the research on the planting technology of China HUANENG photovoltaic tea garden (HNKJ2022-H135).
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.