Tissue-specific patterns of a maize Myb transcription factor are epigenetically regulated

The maize p1 gene encodes a Myb-homologous regulator of red pigment biosynt hesis. To investigate the tissue-specific regulation of the p1 gene, maize plants were transformed with constructs combining promoter and cDNA sequenc es of two alleles; which differ in pigmentation patterns: P1-wr (white peri carp/red cob) and P1-rr (red pericarp/red cob). Surprisingly, all promoter/ cDNA combinations produced transgenic plants with red pericarp and red cob (RR pattern), indicating that the P1-wr promoter and encoded protein can fu nction in pericarp. Some of the RR patterned transgenic plants produced pro geny plants with white pericarp and red cob (WR pattern), and this switch i n tissue-specificity correlated with increased transgene methylation. A sim ilar inverse correlation between pericarp pigmentation and DNA methylation was observed for certain natural p1 alleles, which have a gene structure ch aracteristic of standard P1-wr alleles, but which confer red pericarp pigme ntation and are consistently less methylated than standard P1-wr alleles. A lthough we cannot rule out the possible existence of tissue-specific regula tory elements within the p1 non-coding sequences or flanking regions, the d ata from transgenic and natural alleles suggest that the tissue-specific pi gmentation pattern characteristic of the P1-wr phenotype is epigenetically controlled.