Transposon Insertions in the Promoter of the Zea mays a1 Gene Differentially Affect Transcription by the Myb Factors P and C1

The understanding of control of gene regulation in higher eukaryotes relies heavily on results derived from non-in vivo studies, but rarely can the significance of these approximations be established in vivo. Here, we investigated the effect of Mutator and Spm insertions on the expression of the flavonoid biosynthetic gene a1, independently regulated by the transcription factors C1 and P. The a1-mum2 and a1-m2 alleles carry Mu1 and Spm insertions, respectively, in a cis-element (ARE) of unknown function located between the P- and C1-binding sites. We show that the insertions of Mu1 and Spm similarly influence the expression of a1 controlled by C1 or P. The P-controlled a1 expression in a1-m2 is Spm dependent, and the mutant phenotype of a1-mum2 is suppressed in the pericarp in the absence of the autonomous MuDR element. Footprints within the ARE affect the regulation of a1 by C1 and P differently, providing evidence that these factors control a1 expression using distinct cis-acting regulatory elements. Together, our findings contribute significantly to one of the best-described plant regulatory systems, while stressing the need to complement with in vivo experiments current approaches used for the study of control of gene expression.