The R2R3-MYB transcription factor SsMYB1 positively regulates anthocyanin biosynthesis and determines leaf color in Chinese tallow (Sapium sebiferum Roxb.)

Anthocyanin, a class of secondary metabolite, is critical for the distinctive autumn leaf coloration in landscape trees. Understanding the mechanism of anthocyanin regulation is essential to gardening applications. In this study, an R2R3-MYB transcription factor SsMYB1 was identified from Chinese tallow (Sapium sebiferum Roxb.), a kind of ornamental tree widely planted in China. The anthocyanin content of Chinese tallow leaves was dependent on the expression of SsMYB1. Overexpressing the SsMYB1 in Arabidopsis showed higher anthocyanin contents, whereas silencing of SsMYB1 in the Chinese tallow leaves significantly reduced its accumulation. The basic helix-loop-helix protein SsbHLH1, which acted as a putative SsMYB1 co-regulator, directly interacted with SsMYB1 to regulate the anthocyanin biosynthetic pathway, which was further confirmed by yeast two-hybridization and bimolecular fluorescence complementation assays. In addition, tobacco leaves transient overexpressing SsMYB1 and SsbHLH1 showed deeper red pigmentation compared with SsMYB1 alone. The results also showed that SsMYB1 activated anthocyanin biosynthesis by directly binding to the promoters of SsDFR1 and SsANS and promoted their transcription activity, which can be further enhanced by SsbHLH1. Collectively, our results indicated that SsMYB1 positively regulates the anthocyanin biosynthesis and leaf coloration in Chinese tallow.