<i>CsUGT89A2</i> enhances tea plant resistance to <i>Toxoptera aurantia</i> by mediating flavonoid glycosides biosynthesis

Tea plant [<i>Camellia sinensis</i> (L.) O. Kuntze] is a globally important crop but is severely threatened by <i>Toxoptera aurantia</i> infestations, which impact yield and safety. However, the response of tea plants to aphid feeding remains largely unexplored. This study investigates the feeding behavior of <i>T. aurantia</i> on different cultivars and identifies 'Huangjinya' and 'Qiancha 1' as susceptible and resistant cultivars, respectively. Transcriptome analysis revealed that <i>CsUGT89A2</i> was significantly upregulated in response to <i>T. aurantia</i> infestation. <i>In vitro</i> biochemical assays demonstrated that <i>CsUGT89A2</i> encodes a flavonoid 7-glycosyltransferase that catalyzes the conversion of flavonoids and UDP-glucose into flavonoid 7-<i>O</i>-glucosides. <i>In vivo</i>, silencing <i>CsUGT89A2</i> significantly reduced flavonoid glycoside accumulation. To further clarify the role of <i>CsUGT89A2</i> in tea plant resistance to <i>T. aurantia</i>, we used tobacco and tea flowers to evaluate aphid feeding and reproduction under chemical treatment, gene silencing, and gene overexpression conditions. Statistical analysis showed that, compared with flavonoids, the application of flavonoid 7-<i>O</i>-glycosides significantly reduced <i>T. aurantia</i> reproductive capacity. Furthermore, compared with the control, overexpression of <i>CsUGT89A2</i> significantly reduced the reproductive ability of aphids, while its silencing increased reproductive rates. Overall, our findings demonstrate that <i>CsUGT89A2</i> mediates flavonoid glycosylation and enhances insect resistance in tea plants by increasing flavonoid glycoside levels, offering new insights into the role of flavonoid glycosides in the insect resistance of <i>C. sinensis</i>.