Amino Acid Metabolism and Its Molecular Regulation in Oat Seedlings Under Sodium Selenite Treatment

Selenium (Se) influences plant growth, yet its molecular regulation of amino acid metabolism in oat seedlings remains unclear. Through transcriptomic and metabolomic analyses, this study identified three major affected pathways: tryptophan metabolism (16 differentially expressed genes [DEGs], 13 differentially expressed metabolites [DEMs]), glycine, serine, and threonine metabolism (19 DEGs, 10 DEMs), and arginine and proline metabolism (24 DEGs, 13 DEMs). The T0.02 treatment (0.02 g/kg Na2SeO3) precisely regulates metabolism by selectively upregulating dimethylglycine in the glycine, serine, and threonine pathway and activating key genes (PRODH2, amiE2, AMD2) in the arginine–proline pathway, thereby promoting the growth of oat seedlings. The T0.1 treatment (0.1 g/kg Na2SeO3), promoted the accumulation of glycerate and threonine by upregulating the expression of two key genes (HPR3, ItaE1) related to glycine, serine, and threonine metabolism. Simultaneously, it enhanced the accumulation of L-ornithine, putrescine, 4-guanidinobutyric acid, and γ-aminobutyric acid through the upregulation of four key genes (ARG, ODC1, amiE1, and ALDH3) associated with arginine and proline metabolism. Additionally, the upregulation of key genes (ALDH2, 5-HTP) involved in tryptophan metabolism facilitated the accumulation of 5-methoxyindoleacetic acid and serotonin. This study primarily reveals the accumulation patterns of amino acid metabolites in oat seedlings subjected to selenium treatment and identifies key genes and metabolic pathways involved in the molecular response process. Furthermore, the research preliminarily elucidates potential regulatory nodes through which selenium treatment enhances amino acid accumulation, providing significant insights for understanding the comprehensive effects of selenium treatment on the stress resistance mechanisms of oat seedlings.