An R2R3-MYB transcription factor CmMYB21 represses anthocyanin biosynthesis in color fading petals of chrysanthemum

•CmMYB21 is an R2R3-MYB transcription factor belonging to subgroup 19.•The expression levels of CmMYB21 were up-regulated in color fading petals.•CmMYB21 represses CmDFR expression by binding to its promoter.•Overexpression of CmMYB21 suppressed the floral coloration and anthocyanin accumulation in tobacco petals. Flower color is one of the most important traits in ornamental plants. Color fading due to the loss of anthocyanins is a common phenomenon during the flowering process. Here, an R2R3-MYB gene CmMYB21, which was up-regulated in petals during flower color fading process, was isolated from a chrysanthemum cultivar ‘Anastasia Pink’ and functionally characterized. The CmMYB21 protein belonging to subgroup 19, is localized in the nucleus and has no transcriptional activation activity. Additionally, we found that CmMYB21 directly represses CmDFR expression by binding to its promoter. Ectopic over-expression of CmMYB21 in tobacco suppressed anthocyanin accumulation and NtDFR expression in petals. This work suggests that CmMYB21 participates in regulating floral color fading in chrysanthemum by actively suppressing anthocyanin biosynthesis.