A new MADS-box gene (IbMADS10) from sweet potato (Ipomoea batatas (L.) Lam) is involved in the accumulation of anthocyanin

A new MADS-box gene designated as IbMADS10 was cloned and its expression was characterized from sweet potato (Ipomoea batatas (L.) Lam.) cv. Beniazuma. The deduced amino acid sequence of the gene indicated high homology with members of the MADS-box family of transcription factors. IbMADS10 shares high amino acid sequence similarity with the DEFH28 of Antirrhinum majus (64%) and with BpMADS4 of Betula pendula (61%) of the SQUA subfamily. Southern blot analysis revealed that the IbMADS10 is present in one or low copy number in the sweet potato genome. The gene is specifically expressed in the pigmented tissues such as in the flower bud, in the pink and in red roots, and hence, it was speculated that the IbMADS10 gene might be correlated with anthocyanin biosynthesis in sweet potato. RNA blot expression of the anthocyanin biosynthesis genes encoding for CHS, CHI, F3H, DFR, ANS and UFTG carried out in the tissues where the IbMADS10 gene was expressed revealed similar transcript levels in all tissues where the IbMADS10 gene is highly expressed, indicating that the IbMADS10 gene is highly correlated with the anthocyanin biosynthesis genes. Another important aspect is the pigmented phenotypes of transgenic calli that ectopically express the IbMADS10 gene, thereby supporting its involvement in the developmental regulation of pigment formation. Tissue printing result further strengthens the hypothesis that the IbMADS10 gene is indeed involved in anthocyanin pigmentation in sweet potato. As the purpose of the IbMADS10 gene is pigmentation, its function, therefore, resembles that of the transparent testa (tt) genes of Arabidopsis.