Combined analysis of transcriptome and metabolome provides insights into nano-selenium foliar applications to improve summer tea quality (Camellia sinensis)

Summer tea quality deteriorates with its inferior taste features. Exogenous nano-selenium (Se) supplementation is an effective device to improve crop quality and economic value; however, the effects of nano-Se on summer tea quality remain unclear. This study aimed to illustrate the effects of foliar application of nano-Se on summer tea leaf quality by integrating metabolomics and transcriptomics approaches. Nano-Se enhanced Se content in tea leaves. Further, nano-Se significantly decreased the total tea polyphenols, catechin, and caffeine contents but increased total amino acids and theanine contents, markedly lowering the ratio of tea polyphenols/amino acids as well. Sensory evaluation indicated that nano-Se reduced the bitterness and astringency and improved the umami and sweet tastes of the tea infusion. A total of 130 compounds were identified in the metabolome. Levels of most phenolic compounds were decreased after nano-Se treatment. Association analysis depicted that a total of 30 differentially expressed genes (DEGs) related to catechin (18), caffeine (7), and theanine (5) biosynthetic pathways were influenced by nano-Se. Several transcription factors were identified to interact with these DEGs. Our findings indicate that foliar application of nano-Se can significantly improve summer tea quality, and provide new insight into the application of nano-Se in tea plants.