Quantitative trait loci and metabolic pathways: Genetic control of the concentration of maysin, a corn earworm resistance factor, in maize silks

Interpretation of quantitative trait locus (QTL) studies of agronomic traits is limited by lack of knowledge of biochemical pathways leading to trait expression, To more fully elucidate the biological significance of detected QTL, we chose a trail that is the product of a well-characterized pathway, namely the concentration of maysin, a C-glycosyl flavone, in silks of maize, Zea mays L. Maysin is a host-plant resistance factor against the corn earworm, Helicoverpa tea (Boddie). We determined silk maysin concentrations and restriction fragment length polymorphism genotypes at flavonoid pathway loci or linked markers for 285 F-2 plants derived from the cross of lines GT114 and GT119, Single-factor analysis of variance indicated that the pi region on chromosome 1 accounted for 58.0% of the phenotypic variance and showed additive gene action. The pi locus is a transcription activator for portions of the flavonoid pathway. A second QTL, represented by marker umc105a near the brown pericarp1 locus on chromosome 9, accounted for 10.8% of the variance. Gene action of this region was dominant for low maysin, but was only expressed in the presence of a functional pi allele, The model explaining the greatest proportion of phenotypic variance (75.9%) included pi, umc105a, umc166b (chromosome 1), r1 (chromosome 10), and two epistatic interaction terms, pi x amc105a and pi x r1. Our results provide evidence that regulatory loci have a central role acid that there is a complex interplay among different branches of the flavonoid pathway in the expression of this trait.