The maize p1 locus coincides with a major QTL (quantitative trait locus) determining levels of maysin, a C-glycosyl flavone that deters feeding by corn ear-worm. The p1 gene is tightly linked with a second gene, p2, and both genes encode similar Myb-domain proteins. We show here that maize cell cultures transformed with either the p1or p2 genes expressed under a constitutive promoter accumulate transcripts for flavonoid biosynthetic genes, and synthesize phenylpropanoids and C-glycosyl flavones related to maysin. Additionally, maize plants that are deleted for the p1 gene have reduced maysin levels and moderate silk-browning reaction, whereas plants with a deletion of both p1 and p2 have non-detectable silk maysin and non-browning silks. We conclude that both p1 and p2 induce maysin biosynthesis in silk, although the two genes differ in their expression and pigmentation effects in other tissues. These results show that a QTL for flavone biosynthesis actually comprises two tightly linked genes with related functions.