An omics strategy increasingly improves the discovery of genetic loci and genes for seed-coat color formation in soybean

The phenotypic color of seeds is a complex agronomic trait and has economic and biological significance. The genetic control and molecular regulation mechanisms have been extensively studied. Here, we used a multi-omics strategy to explore the color formation in soybean seeds at a big data scale. We identified 13 large quantitative trait loci (QTL) for color with bulk segregating analysis in recombinant inbreeding lines. GWAS analysis of colors and decomposed attributes in 763 germplasms revealed associated SNP sites perfectly falling in five major QTL, suggesting inherited regulation on color during natural selection. Further transcriptomics analysis before and after color accumulation revealed 182 differentially expression genes (DEGs) in the five QTL, including known genes CHS, MYB, and F3 & PRIME;H involved in pigment accumulation. More DEGs with consistently upregulation or downregulation were identified as shared regulatory genes for two or more color formations while some DEGs were only for a specific color formation. For example, five upregulated DEGs in QTL qSC-3 were in flavonoid biosynthesis responsible for black and brown seed. The DEG (Glyma.08G085400) was identified in the purple seed only, which encodes gibberellin 2-beta-dioxygenase in the metabolism of colorful terpenoids. The candidate genes are involved in flavonoid biosynthesis, transcription factor regulation, gibberellin and terpenoid metabolism, photosynthesis, ascorbate and aldarate metabolism, and lipid metabolism. Seven differentially expressed transcription factors were also speculated that may regulate color formation, including a known MYB. The finds expand QTL and gene candidates for color formation, which could guide to breed better cultivars with designed colors.