Transcriptome analysis revealed the effect of blue and red light on theanine content in Baojing Huangjincha tea

Camellia sinensis 'Baojing Huangjincha 1' (BJHJC), a high-theanine cultivar of tea dominant in Hunan province, experiences a rapid decline in decline in late spring. Light is essential for regulating the growth and metabolite accumulation of tea plants. However, the way light quality influences theanine accumulation in tea is not well understood. Here, under different light conditions (white, blue, red, blue/red (2:1), and red/blue (2:1)), we observed the changes in theanine content in BJHJC leaves. The results showed that theanine content significantly increased under blue and blue/red (2:1) light compared with white, whereas an opposite trend was observed under red and red/blue (1:2) light. Transcriptome analysis revealed that compared with white light, the blue and blue/red (2:1) treatments exhibited a greater number of differentially expressed genes (DEGs), 1,394 and 3,298 respectively, indicating more pronounced transcriptional changes induced by blue light than red light. Furthermore, these DEGs were categorized into five major Kyoto Encyclopedia of Genes and Genomes biological pathways, including primary metabolism, amino acid/glycine–serine–threonine pathways, and carotenoid/chlorophyll metabolism, consistent with the observed changes in theanine and chlorophyll. Meanwhile, the expression of the theanine biosynthesis-related genes CsTS and CsSAMDC was significantly upregulated under blue light, corroborated by real-time quantitative polymerase chain reaction results. Weighted gene co-expression network analysis also screened the genes CsNHL and CsCML42 with the highest eigengene connectivity value, may be the hub genes for the regulation of theanine metabolism by red–blue light. In conclusion, this study examines how varying light quality affects theanine accumulation in tea plants, aiming to provide an effective technical means for improving the economic value of BJHJC.