QUANTITATIVE TRAIT LOCI AND METABOLIC PATHWAYS

The interpretation of quantitative trait locus (QTL) studies is limite d by the lack of information on metabolic pathways leading to most eco nomic traits. inferences about the roles of the underlying genes with a pathway or the nature of their interaction with other loci are gener ally not possible. An exception is resistance to the corn earworm Heli coverpa zea (Boddie) in maize (Zea mays L.) because of maysin, a C-gly cosyl flavone synthesized in silks via a branch of the well characteri zed flavonoid pathway. Our results using flavone synthesis as a model QTL system indicate: (i) the importance of regulatory loci as QTLs, (i i) the importance of interconnecting biochemical pathways on product l evels, (iii) evidence for ''channeling'' of intermediates, allowing in dependent synthesis of related compounds, (iv) the utility of QTL anal ysis in clarifying the role of specific genes in a biochemical pathway and (v) identification of a previously unknown locus on chromosome 9S affecting flavone level. A greater understanding of the genetic basis of maysin synthesis and associated corn earworm resistance should lea d to improved breeding strategies. More broadly, the insights gained i n relating a defined genetic and biochemical pathway affecting a quant itative trait should enhance interpretation of the biological basis of variation for other quantitative traits.