Regulatory mechanism of anthocyanin biosynthesis in Dendrobium officinale : Integrating metabolome and transcriptome to reveal the potential application for quality improvement

The MYB and bHLH transcription factors could participate in the synthesis of anthocyanins through interaction or upstream-downstream regulation. Anthocyanins, as one of the most important active substances in plants, have high nutritional value of human beings. At present, anthocyanin biosynthesis has been widely studied, however, the regulatory mechanism of anthocyanins in Dendrobium officinale (D. officinale) remain unknow. Here, the anthocyanin components of two different colored cultivars from D. officinale were analyzed by UPLC-MS/MS. We have found that delphinidin and its derivatives were the main anthocyanin components in D. officinale, among which Malvidin-3-O-glucoside and Malvidin-3-O-galactoside were the main active substances. Subsequently, the key structural genes DoCHS1/2, DoF3H, DoF3’H, DoDFR1/2, DoANS, and transcription factors DoMYB5–1, DoMYB7, DobHLH5–1 were identified based on transcriptomic analysis, which were mainly involved in the anthocyanin biosynthesis. Among that, both DoMYB5–1 and DoMYB7 could interact with DobHLH5–1 to form complexes (DoMYB5–1-DobHLH5–1, DoMYB7-DobHLH5–1), and then regulated the expression of DoDFR1 and DoF3’H to promote anthocyanin synthesis through the protein-protein interaction, transient overexpression experiments and Y1H assay. Furthermore, we also found that the interaction of DoMYB5–1 and DobHLH5–1 could cascade-rergulate the complex DoMYB7-DobHLH5–1, thereby regulating the expression of DoDFR1 and then participating in the regulation of anthocyanin metabolism in D. officinale. Overall, this study clarified the regulatory mechanism of anthocyanin accumulation in D. officinale, which was helpful to reveal the biological mechanism of secondary metabolism in plants and provided a theoretical reference for the quality improvement of D. officinale.