Genetic Regulation of Anthocyanin Biosynthesis in Cornus Species: The Roles of R2R3-MYB Transcription Factors.

Abstract

Flowering dogwood (Cornus florida L.) and Asian dogwood (Cornus 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 midtone pink bracts "Rosy Teacups") were sampled when color was maximally visible. Differential gene expression analysis of the RNAseq data identified 1156 differentially expressed genes in C. florida and 1396 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 belong to Subgroup 4, whereas CfMYB1 80 and CkMYB1 clustered in Subgroup 5. Genes in the former group repress anthocyanin and proanthocyanidin synthesis in flowering and Asian dogwoods, whereas genes in the latter increase it. Our study contributes to understanding processes behind anthocyanin production and lays the foundation for the future development of molecular markers for faster development of desirable red-bracted dogwoods.