Integrated Transcriptome, microRNA, and Phytochemical Analyses Reveal Roles of Phytohormone Signal Transduction and ABC Transporters in Flavor Formation of Oolong Tea (Camellia sinensis) during Solar Withering

The unique aroma and flavor of oolong
tea develop during the withering
stage of postharvest processing. We explored the roles of miRNA-related
regulatory networks during tea withering and their effects on oolong
tea quality. We conducted transcriptome and miRNA analyses to identify
differentially expressed (DE) miRNAs and target genes among fresh
leaves, indoor-withered leaves, and solar-withered leaves. We identified
32 DE-miRNAs and 41 target genes involved in phytohormone signal transduction
and ABC transporters. Further analyses indicated that these two pathways
regulated the accumulation of flavor-related metabolites during tea
withering. Flavonoid accumulation was correlated with the miR167d_1-ARF-GH3, miR845-ABCC1-3/ABCC2, miR166d-5p_1-ABCC1-2, and miR319c_3-PIF-ARF modules. Terpenoid content was correlated with the miR171b-3p_2-DELLA-MYC2 and miR166d-5p_1-ABCG2-MYC2 modules. These modules inhibited flavonoid biosynthesis and enhanced
terpenoid biosynthesis in solar-withered leaves. Low auxin and gibberellic
acid contents and circRNA-related regulatory networks also regulated
the accumulation of flavor compounds in solar-withered leaves. Our
analyses reveal how solar withering produces high-quality oolong tea.