Opportunities for Modification of Tissue-specific Anthocyanin Accumulation in Solanaceous Crops

Anthocyanins are secondary metabolites derived from the phenylpropanoid pathway with important physiological roles in plant tissues that also influence crop quality and nutritive value.  In flowers, anthocyanins may function as attractants for pollinators and aid in the dispersal of seeds and fruit.  They also function in plant tissues as antioxidants and ultraviolet and visible light protectants.  This class of compounds has generated considerable interest for their presumptive health promoting effects in mitigating or preventing chronic diseases.  Anthocyanin biosynthesis has been studied extensively.  The enzymes in the anthocyanin biosynthetic pathway are functionally conserved across diverse plant species and the genes that encode these enzymes share high sequence similarity across species.  Tissue- or developmental-specific expression exhibited by anthocyanin structural genes is controlled by regulatory genes.  A common set of proteins, comprised of MYB and bHLH MYC proteins plus WD40 repeat proteins, interact to form a regulatory complex that controls transcription of anthocyanin structural genes.  The role of the MYC-MYB-WD40 regulatory protein complex is well accepted for its role in anthocyanin biosynthesis.  Myb and Myc provide one of the best examples of combinatorial plant gene regulation.  Together with the WD40 protein, MYB and MYC provide extensive regulatory function in plants and result in new phenotypic traits by virtue of variation in the MYC or, more commonly, the MYB component.  Gene families with multiple copies of anthocyanin biosynthetic and regulatory genes and resulting variation in function of these genes, particularly for regulatory genes, is responsible for differences in pigmentation and patterns of tissue- or developmental-specific pigmentation within and between species.  Opportunities for modification of anthocyanin composition and tissue-specific pigmentation in selected Solanaceous crops will be discussed.