UV-B and mechanical wounding synergistically induce α-farnesene biosynthesis via CsHY5-CsMYC2 cooperation during oolong tea processing

Abstract

UV-B application enhances the aroma quality of oolong tea; however, the underlying regulatory mechanism remains unclear. This study investigates the regulatory role of UV-B in the biosynthesis of α-farnesene, an important floral and fruity characteristic aroma. UV-B treatment significantly improved the aroma quality of ‘Foshou’ and ‘Yuquan’ oolong teas, increasing α-farnesene levels by 1.8- and 1.4-fold, respectively. The α-farnesene synthase (CsAFS), ELONGATED HYPOCOTYL 5 (CsHY5), and myelocytomatosis protein 2 (CsMYC2) exhibited a highly correlated expression pattern closely associated with α-farnesene accumulation. Single-factor treatment revealed that CsAFS expression was induced by both UV-B and mechanical wounding, with CsHY5 predominantly responding to UV-B radiation, while CsMYC2 primarily responded to tumbling-induced mechanical wounding signal. Transient suppression of CsHY5 in tea leaves reduced the expression of both CsAFS and CsMYC2 whereas CsMYC2 suppression decreased CsAFS expression. G-box motifs were identified in promoters of CsMYC2 and CsAFS, and the dual-luciferase reporter assay (LUC) and electrophoretic mobility shift assays (EMSA) demonstrated direct binding functions of CsHY5 to CsAFS and CsMYC2 promoters, as well as CsMYC2 to the CsAFS promoter. Based on sensory evaluation, odourant quantification, gene expression, and molecular functional analysis, we propose that UV-B radiation and tumbling-induced wounding signals synergistically regulate α-farnesene biosynthesis through a coordinated interaction of CsHY5 and CsMYC2 during oolong tea processing. These findings improve our understanding of flavour formation during oolong tea production and also provide novel insights into artificial light application in tea manufacturing.