Isolation of a WD40-repeat gene regulating anthocyanin biosynthesis in storage roots of purple-fleshed sweet potato

Many transcriptional factors including the R2R3-MYB domain, basic helix-loop-helix (bHLH) domain and WD40 repeat proteins, which regulate flavonoid biosynthesis, have been identified in various plant species. However, there is little information on WD40 proteins in underground organs. In this study, a WD40-repeat protein gene was isolated from purple-fleshed sweet potato (Ipomoea batatas (L.) Lam. cv. Yamakawamurasaki) (IbWD40). The expression patterns of this gene were positively correlated with anthocyanin accumulation in different sweet potato cultivars. An IbWD40-GFP fusion protein was observed only in the nucleus of onion epidermal cells, which was consistent with its role as a transcriptional regulator. Stable transformation analysis revealed that IbWD40 was up-regulated in Arabidopsis thaliana seedlings, which accumulated anthocyanins, with possible additional effects on the formation of other flavonoid compounds in other tissues. These results suggest that in storage roots of purple-fleshed sweet potato the activity of IbWD40 plays a critical role in the regulation of anthocyanin biosynthesis.