RsTTG1, a WD40 Protein, Interacts with the bHLH Transcription Factor RsTT8 to Regulate Anthocyanin and Proanthocyanidin Biosynthesis in .

MBW complexes, consisting of MYB, basic helix-loop-helix (bHLH), and WD40 proteins, regulate multiple traits in plants, including anthocyanin and proanthocyanidin (PA) biosynthesis and the determination of epidermal cell fate. Here, a WD40 gene from , designated (), was cloned and functionally characterized. Heterologous expression of in the mutant background restored accumulation of anthocyanin and PA in the mutant and rescued trichome development. In radish, was abundantly expressed in all root and leaf tissues, independently of anthocyanin accumulation, while its MBW partners and () were expressed at higher levels in pigment-accumulating tissues. In yeast two-hybrid analysis, the full-length RsTTG1 protein interacted with RsTT8. Moreover, transient protoplast co-expression assays demonstrated that RsTTG1, which localized to both the cytoplasm and nucleus, moves from the cytoplasm to the nucleus in the presence of RsTT8. When co-expressed with and , stably activated the promoters of the anthocyanin biosynthesis genes () and (). Transient expression of in tobacco leaves exhibited an increase in anthocyanin accumulation due to activation of the expression of anthocyanin biosynthesis genes when simultaneously expressed with and . These results indicate that RsTTG1 is a vital regulator of pigmentation and trichome development as a functional homolog of AtTTG1.