Transformation of maize with the p1 transcription factor directs production of silk maysin, a corn earworm resistance factor, in concordance with a hierarchy of floral organ pigmentation

The maize p1 gene encodes an R2R3-MYB transcription factor that controls the biosynthesis of red flavonoid pigments in floral tissues of the maize plant. Genetic and quantitative trait locus analyses have also associated the p1 gene with the synthesis of maysin, a flavone glycoside from maize silks that confers natural resistance to corn earworm. Here, we show directly that the p1 gene induces maysin accumulation in silk tissues. Transformation of maize plants that had low or no silk maysin with p1 transgenes elevated silk maysin concentrations to levels sufficient for corn earworm abiosis. The p1 transgenes also conferred red pigment to pericarp, cob, husk and tassel tissues, as expected; however, different subsets of these tissues were pigmented within individual transgenic plants. Statistical analysis shows that the pigmentation patterns observed amongst the p1 transgenic plants conform to a hierarchy that is similar to the temporal ordering of floral organ initiation. We propose that the observed hierarchy of pigmentation patterns is conferred by variation due to epigenetic control of the p1 transgenes. The production of plants with improved traits through genetic engineering can depend in large part on the achievement of tight organ-specific expression of the introduced transgenes. Our results demonstrate that the production of transgenic plants using a promoter with well-defined tissue specificity, such as the p1 promoter, can result in unexpected variation in tissue specificity amongst the resulting transgenic plants.