THE MYB-HOMOLOGOUS P-GENE CONTROLS PHLOBAPHENE PIGMENTATION IN MAIZE FLORAL ORGANS BY DIRECTLY ACTIVATING A FLAVONOID BIOSYNTHETIC GENE SUBSET

The maize P gene, which specifies red pigmentation of the kernel pericarp, cob, and other floral organs, has been an important model since the early days of modern genetics. Here we show that P encodes a Myb homolog that recognizes the sequence CCT/ACC, in sharp contrast with the (C)/(T)AACGG bound by vertebrate Myb proteins. P binds to and activates transcription of the A1 gene required for 3-deoxy flavonoid and phlobaphene biosynthesis, but not the Bz1 gene required for anthocyanin biosynthesis. The maize C1 gene, which also encodes a Myb homolog, activates both the A1 and Bz1 genes, but only in the presence of basic-helix-loop-helix coactivator encoded by the maize genes R or B. These results indicate that Myb homologs can differentially regulate gene expression by binding different DNA sequences, through combinatorial interactions with other factors, or both.