Genotypic Contrasting of Protein and Flavonoid Contributes to Differential Responses of Targeted Metabolites in Soybean Seeds

Soybean is a major source of various nutrients. Increasing demand for soybeans has created considerable impetus for exploring the nutritional quality of soybeans. We aimed to collect soybean varieties rich in nutrients.

Metabolite analysis was carried out for seed compositions, including protein, phenolics, and flavonoids, along with gene expression of protein and phenolic metabolism-related enzymes in 10 soybean accessions collected from different geographical regions.

Total protein content ranged from 29.7% to 35.7%, depending on soybean germplasm accessions. Among them, Vang Ha Giang (VHG) exhibited relatively high protein content, while Cuc Vo Nhai (CVN) had comparatively low protein content. Further analysis of seed compounds indicated that the phenolic compounds were higher in cultivars Dau Tuong Den (DTD) and CVN, with a total phenolic content of 37.7 µg g^-1 and total flavonoid of 2.1 mg g^-1. These results were reinforced by analysis of gene expression levels of candidate genes β-conglycinin (7S) and glycinin (11S) involving protein storage, phenylalanine ammonia-lyase 1 (GmPAL1) and chalcone synthase 8 (GmCHS8) genes related to phenolic and flavonoid synthesis, which showed similar correlation. We revealed that protein content was correlated with seed weight but not with seed color, even though significant variations were found among soybean genotypes, while flavonoid was affected by seed coat color. Furthermore, the negative correlation of protein with flavonoids demonstrated intricate relationships among seed components.

Protein and flavonoid alteration in seeds is subject to major-effect-genotypes in landrace and breeding cultivar selection, and genotype variants are relevant to geographical regions. Our study provides intricate relationships among seed nutritional components and offers insight into the alteration of soybean quality.