Regulatory effects of different proportions of far‐red light on key metabolic components in tea plants ( Camellia sinensis L. )

BACKGROUND: Tea flavor and its health benefits are largely determined by secondary metabolites such as theanine, caffeine, and tea polyphenols, which are influenced by environmental factors, including light. Although far-red (FR) light has attracted increasing attention, its specific regulatory effects on tea plant metabolism remain unclear. In this study, the tea cultivar 'Baihaozao' was exposed to different proportions of FR light (20%, 30%, and 40% of the white-light spectrum) under field conditions, with natural light as the control. RESULTS: Far-red light significantly promoted the accumulation of theanine, which was positively correlated with the increasing FR proportion. Caffeine content showed an overall decreasing trend under higher FR ratios, whereas catechins and tea polyphenols exhibited no clear pattern. Transcriptome analysis identified 3814 differentially expressed genes (DEGs) in the 20% FR light treatment, 4847 DEGs in the 30% FR light treatment, and 3595 DEGs in the 40% FR light treatment, all compared with the control. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that these DEGs were mainly involved in amino acid metabolism and starch and sucrose metabolism. Key genes involved in theanine biosynthesis, including CsTSI, CsGS1.1, and CsAlaDC, were also significantly upregulated, consistent with the increased theanine content. Weighted gene co-expression network analysis further identified multiple genes strongly associated with phyA, which may participate in FR light-mediated regulation of theanine biosynthesis in tea plants. CONCLUSION: Far-red light acts as a specific spectral signal that modulates metabolic pathways in tea plants, mainly enhancing theanine accumulation. These results provide a practical strategy for improving tea quality through spectral regulation under field conditions. © 2026 Society of Chemical Industry.