Identification of an R2R3-MYB gene regulating tepal background coloration in Tricyrtis sp

The liliaceous ornamental plant Tricyrtis sp. produces unique flowers, whose tepals have many random reddish-purple spots on a light purple background. In our previous studies, we performed comprehensive isolation and expression analysis of the anthocyanin biosynthesis-related genes to elucidate the molecular mechanism underlying flower color pattern formation in this plant, and identified the R2R3-MYB transcription factor gene, TrMYB1, expressed in tepals. In the present study, we carried out detailed expression and functional analyses of TrMYB1. Shading treatment of flower buds markedly reduced background coloration of the tepals, while there was little effect on spot formation. In addition, TrMYB1 expression level decreased in the tepals of shaded flower buds. Overexpression of TrMYB1 in Tricyrtis sp. resulted in deeper coloration and significantly increased anthocyanin content in tepals. RNAi-mediated knockdown of TrMYB1 significantly suppressed the expression of the anthocyanin biosynthetic enzyme genes, resulting in a significant decrease in anthocyanin contents and marked reduction in background coloration in the tepals, with little effect on spot formation. These results indicate that tepal background coloration and spot formation may be regulated by different molecular mechanisms, and that background coloration is likely induced by light through activation of TrMYB1.