Tea (Camellia sinensis) is prized globally not only for its flavor but also for its health-promoting compounds, with theanine standing out for its stress-relieving effects and contribution to tea’s signature umami taste. While nitrogen's influence on theanine levels is well documented, the role of phosphorus—another critical plant nutrient—remains murky. Conflicting evidence across cultivars and growing conditions has made it difficult to draw clear conclusions. Due to these inconsistencies and knowledge gaps, a systematic exploration of how phosphorus affects theanine biosynthesis in tea plants is urgently needed.
In a study (DOI: 10.1093/hr/uhae242) published on August 30, 2024, in Horticulture Research, scientists from Guizhou University revealed how phosphorus levels affect theanine accumulation in tea leaves. By combining transcriptome analysis, molecular biology, and plant transformation techniques, they identified a novel regulatory pathway—CsSPX3-CsPHL7-CsGS1/CsTS1—that mediates the suppression of theanine biosynthesis under high phosphate conditions. Their findings mark a breakthrough in understanding the molecular crosstalk between nutrient signaling and flavor compound production in tea plants.
The research team first observed that increasing phosphate concentrations led to a consistent drop in theanine content in both tea leaves and roots. Transcriptomic profiling showed a suite of genes involved in phosphate and nitrogen signaling were differentially expressed, most notably CsSPX3 and CsPHL7, which were upregulated in high-Pi environments. These two genes exhibited expression patterns that inversely mirrored theanine biosynthesis genes, raising a red flag for potential regulation.
Further experiments confirmed that CsSPX3 physically interacts with CsPHL7, and together they suppress the activity of CsTS1 and CsGS1, two enzymes critical for theanine production. Silencing either gene in tea plants led to a significant increase in theanine content, while overexpressing them resulted in marked reductions. Notably, the CsSPX3-CsPHL7 interaction remained stable regardless of phosphorus levels, whereas CsSPX3's interaction with PHR1, another Pi-signaling protein, occurred only under high-Pi conditions—suggesting a layered control mechanism. These findings unravel a sophisticated network that allows tea plants to fine-tune theanine biosynthesis in response to external phosphorus cues.
“This study sheds light on the genetic machinery that links soil nutrients to tea flavor,” said Professor Litang Lu, the study's senior author. “We've identified a specific regulatory module that suppresses theanine production under high phosphate conditions. This not only deepens our understanding of plant metabolic regulation but also provides molecular targets for improving tea quality through breeding or nutrient management.”
These findings have important implications for both tea cultivation and consumer satisfaction. The identification of the CsSPX3-CsPHL7-CsGS1/CsTS1 module opens up possibilities for breeding tea varieties that maintain high theanine levels even under varying soil conditions. Farmers could also adjust fertilization practices to prevent excessive phosphate application, which may unintentionally degrade tea quality. In the future, genome editing or precision agriculture tools could be used to modulate this pathway, ensuring consistently flavorful and health-beneficial tea, even in the face of shifting environmental or agricultural pressures.
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References
DOI
10.1093/hr/uhae242
Original Source URL
https://doi.org/10.1093/hr/uhae242
Funding information
This study is funded by State Key Laboratory of Geo-Information Engineering and Key Laboratory of Surveying and Mapping Science and Geospatial Information Technology of MNR, CASM (2024-01-07), State Key Laboratory of Spatial Datum, the National Natural Science Foundation of China (42374014, 42004014), and the Fundamental Research Funds for the Central University, and Postgraduate Research & Practice Innovation Program of Jiangsu Province (SJCX24_0203).
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.