GENETIC ANALYSIS OF PHYTOESTROGEN CONTENT IN SOYBEANS AND ANIMAL DIETS

Departments of Plant Soil and General Agriculture; Animal Science, Food and Nutrition, Physiology, Southern Illinois University at Carbondale, IL 62901 USA

The abundance of phytoestrogens in soybean seed can vary up to five fold. Phytoestrogen content and profile can vary by year, soybean geneotype and location. The objective of this study was to determine the proportion of this variation that could be explained by genetic inheritance and to identify genes underlying the inheritance of phytoestrogen content and profile. We have analyzed samples from within a recombinant inbred line population derived from two popular soybean cultivars, 'Essex' and 'Forrest'. The cultivars contrast for disease resistance, resistance to abiotic stress and phytoestrogen content and so are suitable for inheritance studies for phytoestrogen profile and amount. We found a consistent differences between Essex and Forrest across years and environments whereby Forrest accumulated more total phytoestrogen, daidzein and genestein, but Essex accumulated more glycitin. The recombinant inbred lines showed transgressive segregation for total phytoestrogen, daidzein, genistein and glycitin content. Broad sense heritability estimates indicated that 48-90% of this variability was genetic. By DNA marker mapping and map integration the location of genes involved in the enzymatic synthesis of phytoestrogens from phenylalanine were compared with inheritance data. We have shown that the 81% of the variability of total genistein content is associated with a genomic region that contains a cluster of chalcone synthase genes and their regulatory factors. Chalcone synthase catalyzes an early step in isoflavone synthesis. Individual soybean phytoestrogens can effect a number of physiological events in mammals. Animal feeding studies have demonstrated species specific effects of phytoestrogens (and of individual phytoestrogens) in rats and pigs. Traits altered include body fat, fecundity and cellular responses to estrogens. Using DNA markers in breeding selection we can reduce detrimental phytoestrogens and enhance beneficial phytoestrogens. This research was supported by the Illinois Council on Food and Agricultural Research and the Illinois Soybean Program Board.