pl-bol3, a complex allele of the anthocyanin regulatory pl1 locus that arose in a naturally occurring maize population

The pl1 gene encodes a MYB-related transcriptional activator committed to the regulation of anthocyanin biosynthesis in maize. Here, we report the genetic and molecular characterisation of pl-bol3, an Andean allele displaying features that make it different from all the known pl1 alleles. pl-bol3 has partial, light-independent expression, and it is active mainly in the juvenile phase of growth. It has a complex molecular structure, containing multiple pl1 gene copies, thus being the first complex locus discovered in the c1/pl1 family. Although the composite genes of the complex locus encode proteins identical to other functional PL1 proteins, the putative promoters of the pl-bol3 gene are different from the promoters of Pl-Rhoades (Pl-Rh) and pl1 sun-red alleles. The intensity and the tissue specificity of anthocyanin production directed by pl-bol3 differ significantly from that of Pl-Rh and the original pl-W22, and are specified by the interaction of pl-bol3 with the different r1/b1 gene family members and the competence of pl-bol3 to different pigment tissues. This allele represents a natural example of gene duplication and diversification of expression, giving rise to a significant change in phenotype and, in this way, is analogous to the complex r1 locus in maize. Analysis of the pl-bol3 allele contributes to understanding the generation of diversity associated with multiple-copy genes and the molecular basis of allele-specific gene expression.