Deciphering the Regulatory Network and Underlying Mechanism for Flavonoid Biosynthesis in Soybean (Glycine max L)

Soybean flavonoids are important for plant growth and defense as well as human nutrition. Great efforts have been made to understand the flavonoid biosynthesis and regulation in allopolyploid soybean; e.g. quantitative trait loci for anthocyanin accumulation in seeds, flowers, and hypocotyls and isoflavone production in soybean varieties have been explored. However, little is known about their regulatory mechanisms. We have noticed that anthocynanin or proanthocyanidin production is often negatively correlated with isoflavonoid biosynthesis, while the mechanisms underlying the counteraction between anthocyanin and isoflavonoid accumulation in plant is not clear. In tetraploid soybean genome, the components of the well-known regulatory complex MYB-B-HLH-WD40 (MBW) and other MYB factors negatively regulating flavonoids in a temporal-spatial patterns in other model plants exist in multiple copies and their functional evolution (de-,sub-, or neo-functionalization) are not evaluated. In our studies, transcriptional regulators of anthocyanin and proanthocyanidin biosynthesis were shown to negatively regulate isoflavone accumulation. We investigated the mechanisms by combined transcriptomic analysis, metabolic profiling, and biochemical approaches to dissect how these transcription factors and their complex regulate anthocyanin, proanthocyanidin isoflavone production to distinguish each single copy’s function. It was revealed that several of these regulators may directly regulate the expression of IFS and other isoflavone biosynthetic genes, whereas others may indirectly impact on isoflavone through feedback regulatory loops. The known QTL loci and GWAS candidate genes are partially consistent with these transcription factors in regulations of isoflavone production in soybean.