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 peric arp, cob, and other floral organs, has been an important model since t he early days of modern genetics. Here we show that P encodes a Myb ho molog that recognizes the sequence CCT/ACC, in sharp contrast with the (C)/(T)AACGG bound by vertebrate Myb proteins. P binds to and activat es transcription of the A1 gene required for 3-deoxy flavonoid and phl obaphene biosynthesis, but not the Bz1 gene required for anthocyanin b iosynthesis. The maize C1 gene, which also encodes a Myb homolog, acti vates both the A1 and Bz1 genes, but only in the presence of basic-hel ix-loop-helix coactivator encoded by the maize genes R or B. These res ults indicate that Myb homologs can differentially regulate gene expre ssion by binding different DNA sequences, through combinatorial intera ctions with other factors, or both.