Genetic regulation of anthocyanin biosynthesis in Cornus species: The roles of R2R3-MYB transcription factors

Flowering dogwood (Cornus florida L.) and Asian dogwood (C. kousa F. Buerger ex Hance) are popular deciduous ornamental trees native to a wide range of the eastern and southeastern United States and East Asia, respectively. Anthocyanin pigments enhance desirable pink or dark red colored bracts in dogwoods. Although anthocyanin biosynthesis is one of the best-studied biological processes in nature, genomic and genetic resources to understand the molecular regulation of its synthesis in dogwoods are still lacking. Two classes of genes control anthocyanin production; both structural genes and MYB transcription factors may function as positive or negative regulators of anthocyanin biosynthesis. To reveal the molecular mechanisms that govern color production in ornamental dogwoods, mature bracts of three cultivars of C. florida (white bracts: Cloud Nine; red bracts: Cherokee Brave and Cherokee Chief) and two cultivars of C. kousa (light green bracts: Greensleeves and mid-tone pink bracts Rosy Teacups) were sampled when color was maximally visible. Differential gene expression analysis of the RNAseq data identified 1,156 differentially expressed genes in C. florida and 1,396 in C. kousa. Phylogenetic analysis with functional orthologues in other plants grouped the candidate R2R3-MYB identified in this study into two distinct subgroups. CfMYB2, CfMYB3, and CkMYB2 belonged to subgroup 4, whereas CfMYB1 80 and CkMYB1 clustered in subgroup 5. The former repress anthocyanin and proanthocyanidin synthesis in flowering and Asian dogwoods, whereas the latter increase it. Our study contributes to understanding processes behind anthocyanin production and lays foundation to future development of molecular markers for faster development of desirable red-bracted dogwoods.