Abstract
BackgroundSoybean (Glycine max [L] Merr.) seed isoflavones have long been considered a desirable trait to target in selection programs for their contribution to human health and plant defense systems. However, attempts to modify seed isoflavone contents have not always produced the expected results because their genetic basis is polygenic and complex. Undoubtedly, the extreme variability that seed isoflavones display over environments has obscured our understanding of the genetics involved.ResultsIn this study, a mapping population of RILs with three replicates was analyzed in four different environments (two locations over two years). We found a total of thirty-five main-effect genomic regions and many epistatic interactions controlling genistein, daidzein, glycitein and total isoflavone accumulation in seeds. The use of distinct environments permitted detection of a great number of environment-modulated and minor-effect QTL. Our findings suggest that isoflavone seed concentration is controlled by a complex network of multiple minor-effect loci interconnected by a dense epistatic map of interactions. The magnitude and significance of the effects of many of the nodes and connections in the network varied depending on the environmental conditions. In an attempt to unravel the genetic architecture underlying the traits studied, we searched on a genome-wide scale for genomic regions homologous to the most important identified isoflavone biosynthetic genes. We identified putative candidate genes for several of the main-effect and epistatic QTL and for QTL reported by other groups.ConclusionsTo better understand the underlying genetics of isoflavone accumulation, we performed a large scale analysis to identify genomic regions associated with isoflavone concentrations. We not only identified a number of such regions, but also found that they can interact with one another and with the environment to form a complex adaptable network controlling seed isoflavone levels. We also found putative candidate genes in several regions and overall we advanced the knowledge of the genetics underlying isoflavone synthesis.
Highlights
Soybean (Glycine max [L] Merr.) seed isoflavones have long been considered a desirable trait to target in selection programs for their contribution to human health and plant defense systems
Results confirmed that the accumulation of isoflavones in soybean seeds is highly influenced by genetic (G), environmental (E), and G×E interaction effects (P < 0.0001)
Parental lines did not greatly differ in genistein, daidzein and total isoflavones in some environments, considerable transgressive segregation was found, which indicated that both parents bear positive-effect alleles for isoflavone synthesis, and suggested that an elevated number of QTL might be segregating and likely to be detected in the mapping analysis
Summary
Soybean (Glycine max [L] Merr.) seed isoflavones have long been considered a desirable trait to target in selection programs for their contribution to human health and plant defense systems. The extreme variability that seed isoflavones display over environments has obscured our understanding of the genetics involved. Considerable evidence has implicated isoflavones in the fitness of both humans and plants. In a four-location field trial a cultivar was found to fluctuate from 460 to 1950 μg g-1 in its isoflavone levels in seeds. In spite of the environmental interactions, the control of isoflavone content in seeds is largely genetic [14,21,22,23], and numerous minor-effect QTL have been found to determine soybean isoflavone amounts. QTL that are stable over multiple environments are more useful in breeding programs because they might contribute to a consistent phenotype under changing conditions
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