Transcriptomic analysis of the effects of three different light treatments on the biosynthesis of characteristic compounds in the tea plant by RNA-Seq

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The tea plant (Camellia sinensis) is considered an environment-sensitive plant, because the biosynthesis of tea’s characteristic compounds is easily influenced by light quality, ambient temperature, and humidity. The characteristic compounds in tea leaves, especially polyphenols, theanine, and caffeine, are important components that contribute to tea’s flavor. To investigate the effects of light quality on secondary metabolism in young shoots of tea plants at the messenger RNA (mRNA) transcript level, RNA-Seq was performed using one leaf and a bud from tea cultivar 108, which was reared in three different colored light conditions. Plastic film (blue, purple, and yellow) was used to create different monochromatic light conditions, which were compared to natural (white) light treatment as a control. Our results showed that, compared to the control, the 2667, 1938, and 2326 genes were differentially expressed and the 1518, 1032, and 1316 genes were upregulated in blue, purple, and yellow light conditions, respectively. Gene Ontology (GO) analysis indicated that oxidation-reduction, regulation of transcription, and protein phosphorylation were the main enriched biological process terms in all three treatments. Conversely, the top enriched terms in the cellular component and molecular function categories were plasma membrane and ATP binding. Furthermore, KEGG analysis showed that the genes which were downregulated in blue light were enriched for genes in the amino acid biosynthesis, flavonoid biosynthesis, and phenylpropanoid biosynthesis pathways. Similarly, phenylpropanoid biosynthesis and phenylalanine metabolism pathway genes were enriched among the transcripts that were downregulated in purple light and yellow light. Particularly, a few genes encoding enzymes involved in the biosynthesis of catechins, theanine, and caffeine exhibited significantly different expression levels in the different monochromatic light conditions. Compared to purple and yellow light treatments, more genes were differentially expressed in blue light relative to white light. These results demonstrated that light quality affects secondary metabolism in young shoots of the tea plant, and that light color can influence the biosynthesis of characteristic compounds in tea leaves.