Integrated nutrient profiling and metabolomic analysis reveal nutritional enhancement in autotetraploid brown rice

To investigate the effects of polyploidization on the nutritional quality of brown rice, three pairs of homologous diploid and autotetraploid rice lines with a japonica genetic background (GFD, 397, and T13) were examined for grain morphology and nutrient composition, and their metabolite profiles were analyzed using UPLC-MS/MS-based metabolomics. Compared with their diploid counterparts, all three autotetraploid lines produced larger grains. Among the 77 nutritional traits measured, resistant starch, crude fat, and crude protein contents were significantly increased. Protein fraction analysis indicated enhanced accumulation of major storage proteins, and most amino acids, particularly essential amino acids, were present at higher levels in autotetraploid brown rice. Vitamin A content increased significantly, several B vitamins showed an overall increasing trend whose magnitude varied among genotypes, whereas vitamins D content decreased. Overall, chromosome doubling altered nutrient composition through both lines consistent and lines dependent responses. Metabolomic profiling identified 1,211 metabolites, and the differentially abundant metabolites were characterized primarily by the upregulation of amino acids and their derivatives and the downregulation of certain flavonoids. KEGG enrichment analysis further showed that the differentially abundant metabolites were mainly enriched in pathways related to amino acid biosynthesis, suggesting that metabolite accumulation in these pathways may be associated with the increased protein and amino acid contents in autotetraploids, although the underlying mechanisms require further investigation. Collectively, these findings demonstrate indicate that polyploidization is associated with improvement in several nutritional quality of brown rice and provide a basis for the further evaluation and utilization of autotetraploid brown rice.