Involvement of a MYB Transcription Factor in Anthocyanin Biosynthesis during Chinese Bayberry (Morella rubra) Fruit Ripening

SIMPLE SUMMARY: Color is one of the most significant quality characteristics of Chinese bayberry (Morella rubra). Exploration of the anthocyanin biosynthesis mechanism is crucial for the genetic improvement of color quality. Many MYB transcription factors are reported to control the biosynthesis of anthocyanins in a variety of plant species. However, it is still unclear how the MYB genes in Chinese bayberry contribute to the synthesis of anthocyanins. In this research, we isolated the MYB transcription factor, MrMYB9, based on comparative transcriptome analysis of red and white Chinese bayberry fruits. We also profiled MrMYB9 gene expression during the maturation period and in specific tissues. Through bioinformatics and molecular biology experiments, MrMYB9 was subsequently identified as a transcription factor of the R2R3-MYB type associated with anthocyanin biosynthesis. Our research sheds insights on the biosynthesis of anthocyanins during color maturation in the Chinese bayberry. ABSTRACT: Anthocyanin is a class of water-soluble flavonoids found in Chinese bayberry (Morella rubra) that is not only responsible for the variety of colors visible in nature but also has numerous health-promoting benefits in humans. Through comparative transcriptomics, we isolated and identified a transcription factor (TF) of the R2R3-MYB type, MrMYB9, in order to explore the anthocyanin biosynthesis pathway in red and white Chinese bayberries. MrMYB9 transcript was positively correlated with anthocyanin level and anthocyanin biosynthetic gene expression during Chinese bayberry fruit maturation (R-values in the range 0.54–0.84, p < 0.05). Sequence analysis revealed that MrMYB9 shared a similar R2R3 domain with MYB activators of anthocyanin biosynthesis in other plants. MrMYB9 substantially transactivated promoters of anthocyanin biosynthesis-related EBGs (MrCHI, MrF3’H, and MrANS) and LBGs (MrUFGT) upon co-expression of the AtEGL3 gene. Our findings indicated that MrMYB9 may positively modulate anthocyanin accumulation in Chinese bayberry.