Transcriptome and metabolome analyses reveal a key role of the anthocyanin biosynthetic pathway cascade in the pigmentation of a Cinnamomum camphora red bark mutant (‘Gantong 1’)

The camphor tree (Cinnamomum camphora) is an important economic tree due to its aromatic, medicinal and ornamental properties. Color is a key characteristic contributing to the ornamental value of the camphor tree to breeders and consumers. However, little is known about the coloration mechanism in the camphor tree. In this study, a C. camphora red bark mutant ‘Gantong 1’ was obtained and the metabolomics and transcriptomics data of the red bark of ‘Gantong 1’ and the green bark of normal C. camphora were analyzed. A total of 2017 differentially expressed genes (DEGs) and 16 anthocyanin metabolites were identified in the red and green barks. The enrichment analysis revealed that anthocyanin biosynthesis pathways were the most active biological pathways regarding to the upregulated DEGs in the red bark. Integrated analysis of transcriptomics and metabolomics showed that pelargonidin/cyanidin/peonidin-based anthocyanins were the main pigments responsible for the orange-red coloration of the ‘Gantong 1’. A total of 24 upregulated DEGs encoding 11 enzymes were identified as key structural genes participating in the anthocyanin biosynthesis, and 6 transcription factors (3 MYBs and 3 bHLHs) may be candidate regulators of the anthocyanin biosynthesis pathways in the ‘Gantong 1’. Taken together, the results of this study provide not only comprehensive transcriptome and anthocyanin metabolite information but also valuable insights into the coloring mechanism of the camphor tree red bark mutant ‘Gantong 1’.