Comparisons of Maize pericarp color1 Alleles Reveal Paralogous Gene Recombination and an Organ-Specific Enhancer Region

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Abstract
The maize (Zea mays) p1 (for pericarp color1) gene encodes an R2R3 Myb-like transcription factor that regulates the flavonoid biosynthetic pathway in floral organs, most notably kernel pericarp and cob. Alleles of the p1 gene condition distinct tissue-specific pigmentation patterns; to elucidate the molecular basis of these allele-specific expression patterns, we characterized two novel P1-rw (for red pericarp/white cob) alleles, P1-rw1077 and P1-rw751Ac. Structural analysis of P1-rw1077 indicated that this allele was generated by recombination between p1 and the tightly linked paralogous gene, p2. In the resulting gene, the p1 coding sequence was replaced by the p2 coding sequence, whereas the flanking p1 regulatory sequences remained largely preserved. The red pericarp color specified by P1-rw1077 suggests that the p1- and p2-encoded proteins are functionally equivalent as regulatory factors in the flavonoid biosynthesis pathway. Sequence analysis shows that the P1-rw1077 allele lacks a 386-bp sequence in a distal enhancer region 5 kb upstream of the transcription start site. An independently derived P1-rw allele contains an Ac insertion into the same sequence, indicating that this site likely contains cob glume-specific regulatory elements.