Regulation of anthocyanin biosynthesis in antirrhinum

The genetic control of anthocyanin pigmentation in the corolla of the model dicot species Antirrhinum majus (antirrhinum) has been the focus of many studies although little is known about the regulation of the genes encoding the anthocyanin biosynthetic enzymes. In this study, it has been determined that a family of Myb genes containing Venosa and a complex locus comprised of Rosea and Rosea2 is involved in regulating antirrhinum pigmentation, most likely as direct controllers of biosynthetic gene transcription. The predicted proteins encoded by the family show structural features indicative of transcriptional activators and cDNAs encoding the factors were able to induce anthocyanin production in a cell autonomous manner when transiently expressed in rosea:rosea2 mutant petal tissue. Rosea was further shown to alter anthocyanin pigmentation when expressed in heterologous hosts. This study has also focussed on the bHLH regulatory factors that operate with the Myb family members to control anthocyanin pigmentation in antirrhinum. Goodrich et al. (1992) had previously identified Delila as a locus encoding one of these factors. In this study, the Delila-linked Mutabilis locus has been investigated. Northern analysis of anthocyanin biosynthetic gene expression in mutabilis mutant tissue suggests that Mutabilis is a regulatory gene, Furthermore, genetic evidence indicates Delila can complement the mutabilis mutation, suggesting Mutabilis encodes a bHLH factor. Genetic evidence also suggests a specificity regarding which Myb and bHLH factors interact in antirrhinum, a characteristic that has not been previously described for any Myb and bHLH anthocyanin regulators.