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.

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Plants and algae can detect the presence of bacteria via sensing of proteins or peptides of bacterial origin. Flg22, a fragment of bacterial flagellin, is one of these peptides and has been shown to be an effective elicitor in both plants and algae. Here, we investigated the elicitor activity of flg22-derived peptides in the brown alga, Saccharina japonica. By monitoring luminoldependent fluorescence, we could observe that the release of H 2 O 2 induced by flg22-derived peptides is maximal at 2 h after induction. The elicitor activity was depending on the length of the peptides in the order of flg22 > flg15 > flg14. Cytological observations regarding the presence of reactive oxygen species (ROS) after induction were consistent with quantitative measurements of H 2 O 2 generation using a 2′,7′-dichlorofluorescein diacetate (DCFH-DA) fluorescent probe. Addition of 1 μM each of flg22 and flg15 was sufficient to inhibit growth of female gametophytes. Furthermore, the elicitor activity of C-terminally shortened flg15-derived peptides suggests that flg15 apparently is the smallest peptide with elicitor activity. Amino acid position D43 at the N-terminus of a flagellin was demonstrated to be involved in the elicitor activity. Finally, H 2 O 2 was localized in the plasma membranes of female gametophytes by an NADPH oxidase inhibitor and electron-dense deposits of cerium perhydroxide by transmission electron microscope.

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