| Anthocyanin pigment biosynthesis in Zea mays (maize) is a model system of regulated gene expression. Two classes of regulatory proteins proposed to be transcriptional activators, C1 (homologous to Myb) and R (homologous to basic-helix-loop-helix proteins), are required for expression of anthocyanin-specific, enzyme-encoding structural genes, including Anthocyaninless-1 (A1), Bronze-1 (Bz1), and Bronze-2 (Bz2). A mutational analysis of the Bz2 promoter was performed using a sensitive transient gene expression assay to study anthocyanin gene transcriptional regulation.;When electroporated into colorless maize protoplasts, luciferase reporter genes controlled by the Bz2, Bz1, and A1 promoters were expressed only when both R and C1 expression plasmids were co-electroporated. R and C1 also induced mRNA accumulation of the endogenous anthocyanin genes, resulting in pink protoplasts with 24 hr. Deletional analysis of the Bz2 promoter indicated that sequences between ;In separate experiments, anthocyanin pigment accumulation in friable, Type II embryogenic maize callus was observed in a set of genotypes constructed in the inbred line A188. As in intact plant tissues, anthocyanin biosynthesis in embryogenic callus requires both an R-family member (R or B) and a C1-family member (C1 or Pl). By observing which tissue-specific regulatory alleles control pigmentation in culture, I determined that embryogenic callus has similarities to both aleurone and seedling tissues, but does not correspond exactly to any tissue present in intact plants. This information and these maize lines may facilitate use of anthocyanin as a visible marker for stable transformation. |
