*Article* **Upregulation of the MYB2 Transcription Factor is Associated with Increased Accumulation of Anthocyanin in the Leaves of** *Dendrobium bigibbum*

**Gah-Hyun Lim <sup>1</sup> , Se Won Kim 1,2, Jaihyunk Ryu <sup>1</sup> , Si-Yong Kang <sup>1</sup> , Jin-Baek Kim <sup>1</sup> and Sang Hoon Kim 1,\***


Received: 27 July 2020; Accepted: 31 July 2020; Published: 6 August 2020

**Abstract:** Orchids with colorful leaves and flowers have significant ornamental value. Here, we used γ-irradiation-based mutagenesis to produce a *Dendrobium bigibbum* mutant that developed purple instead of the normal green leaves. RNA sequencing of the mutant plant identified 2513 differentially expressed genes, including 1870 up- and 706 downregulated genes. The purple leaf color of mutant leaves was associated with increased expression of genes that encoded key biosynthetic enzymes in the anthocyanin biosynthetic pathway. In addition, the mutant leaves also showed increased expression of several families of transcription factors including the *MYB2* gene. Transient overexpression of *D. biggibum MYB2* in *Nicotiana benthamiana* was associated with increased expression of endogenous anthocyanin biosynthesis genes. Interestingly, transient overexpression of orthologous *MYB2* genes from other orchids did not upregulate expression of endogenous anthocyanin biosynthesis genes. Together, these results suggest that the purple coloration of *D. biggibum* leaves is at least associated with increased expression of the *MYB2* gene, and the *MYB2* orthologs from orchids likely function differently, regardless of their high level of similarity.

**Keywords:** anthocyanin; MYB2; orchid; *Dendrobium bigibbum*; γ-irradiation
