Abstract
Using a combination of biochemical, transcriptomic, and physiological analyses, we elucidated the mechanisms of physical and chemical withering of tea shoots subjected to UV-C and ethylene treatments. UV-C irradiation (15 kJ m-2) initiated oxidation of catechins into theaflavins, increasing theaflavin-3-monogallate and theaflavin digallate by 5- and 13.2-4.4-fold, respectively, at the end of withering. Concomitantly, a rapid change to brown/red, an increase in electrolyte leakage, and the upregulation of peroxidases (viz. Px2, Px4, and Px6) and polyphenol oxidases (PPO-1) occurred. Exogenous ethylene significantly increased the metabolic rate (40%) and moisture loss (30%) compared to control during simulated withering (12 h at 25 °C) and upregulated transcripts associated with responses to dehydration and abiotic stress, such as those in the ethylene signaling pathway (viz. EIN4-like, EIN3-FBox1, and ERFs). Incorporating ethylene during withering could shorten the tea manufacturing process, while UV-C could enhance the accumulation of flavor-related compounds.
Highlights
Black tea accounts for ca. 75% of total world production
The samples were clustered according to the treatment and differentiated from their respective controls; there was no clear separation based on the withering time (Supporting Information Figure S1)
Tea withering is the first of the four steps needed for black tea production
Summary
Black tea accounts for ca. 75% of total world production. Its processing involves four stages: withering, fermentation (oxidation), cutting, and drying.[1,2] Withering brings about both physical (water loss and leaf softening) and chemical changes (important for flavor and aroma development) and is regarded as a crucial stage in the tea manufacturing process.[3]. With the tea reference genome recently becoming available[4] and several transcriptomic analyses published in recent years,[5−7] the molecular mechanisms underpinning the responses of Camellia sinensis to a number of biotic and abiotic stresses, as well as its evolution and adaptation,[8] are being elucidated. Tea trancriptomic analyses have shed light on the gene regulatory responses during cold acclimation,[9] gene regulatory networks for secondary metabolism,[10] and the association between tea quality and stress response.[11] Proteomic changes during tea withering have recently been reported.[12] there has been a lack of research focused on utilizing gene expression data to gain better mechanistic understanding of the black tea withering process
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