A novel transcription factor PsMYBM enhances the biosynthesis of anthocyanins in response to light in tree peony

Light is a vital environmental factor that affects the biosynthesis of anthocyanin, and the ornamental and economic value of ornamental plants can be improved by properly regulating the conditions of light for their growth. Tree peony (Paeonia suffruticosa Andrews), "the king of flowers" in China, is popular in the whole country and contributes to cultivar breeding throughout the world. In the tree peony industry, light affects not only flower color and quality when the cultivation of flowers is forced but also its ornamental value in specific gardens and fields. However, the molecular mechanism on how light regulates the biosynthesis of anthocyanin is unclear. In this study, darkness was found to decrease the pigmentation of flower petals in the tree peony cultivar 'Higurashi'. The differentially expressed genes responsible for anthocyanin biosynthesis were obtained through a comparative transcriptome analysis of flower petals under light/dark conditions. This led to the identification of an R2R3-MYB transcription factor designated PsMYBM. The transient silencing of PsMYBM reduced the biosynthesis of anthocyanins in the petals, while its overexpression promoted the formation of various colors in organs in transgenic tobacco (Nicotiana tabacum cv. Nc89) plants. In addition, it has been demonstrated that PsMYBM can directly activate the promotors of PsCHS and PsF3H. Moreover, light-responsive elements were also identified in the PsMYBM promoter, which could be directly bound by the light signal factor PsHY5. This study illuminates the mechanism of anthocyanin biosynthesis in response to light in tree peony, which could be applied to other woody ornamental plants. It also provides key gene resources to improve the flower color and germplasm innovation.