The CsRAP2.3-CsUGT78A14 module regulates flavonol biosynthesis in white tea trichomes

Flavonols, especially kaempferol derivatives, are highly accumulated in tea trichomes. CsRAP2.3 activates CsUGT78A14 expression to enhance flavonol glycosylation. Overexpression of CsRAP2.3 promotes flavonol biosynthesis in plants. Tea trichomes are rich in secondary metabolites and play a crucial role in the stress resistance and quality formation of tea plants. However, the specific metabolites involved and their regulatory mechanisms remain largely unknown. Here, we employed ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to conduct a comprehensive targeted metabolomic analysis of the trichomes and corresponding defoliated leaves from the buds of Fudingdahao (FDDH) white tea. Our analysis identified a total of 2,425 metabolites, with 1,537 differentially accumulated metabolites (DAMs) between the trichomes and leaves. Notably, flavonoids, particularly kaempferol and its derivatives, were found to be more abundant in trichomes. Transcriptomic analysis revealed 447 genes specifically highly expressed in trichomes, with significant enrichment in phenylpropanoid and flavonoid biosynthesis pathways. Further chromatin accessibility analysis identified an ERF transcription factor, CsRAP2.3, as a key regulator. DNA affinity purification sequencing and luciferase reporter assays demonstrated that CsRAP2.3 binds to the promoter of the CsUGT78A14 gene, which is involved in kaempferol glycosylation. Transient overexpression of CsRAP2.3 in tobacco leaves increased flavonol metabolites. Our results suggest that CsRAP2.3 may regulate the expression of CsUGT78A14 , thereby influencing the accumulation of flavonols in trichomes of tea plants. This study provides insights into the molecular mechanisms underlying the accumulation of flavonol metabolites in white tea trichomes and offers a foundation for improving tea stress resistance and quality.