Transcriptome Analysis of the Effects of Selenium Form and Concentration on Rice Growth and Metabolism at the Seedling Stage

Selenium (Se) is an essential trace element for humans, and the production of Se-enriched rice (Oryza sativa) is a key approach for Se supplementation. Nevertheless, the effects of different Se forms and concentrations on the metabolism and aboveground absorption pathways of rice seedlings are not yet well-understood. Therefore, we conducted a hydroponic experiment and used transcriptome analysis to study the absorption and transformation processes of sodium selenite (Na2SeO3) and selenomethionine (SeMet) in rice at the seedling stage. The aboveground (stem + leaf) Se concentration at the seedling stage was higher under the SeMet treatments, and low Se applications (<25 μM) significantly promoted rice growth. Selenocysteine (SeCys) and SeMet were the primary forms of Se in rice, accounting for 57–86.35% and 7.6–31.5%, respectively, while selenate [Se (VI)] significantly increased when Se levels exceeded 25 μM. In the transcriptome, differentially expressed genes (DEGs) were significantly enriched in the following pathways: carbon metabolism, amino acid biosynthesis, and glutathione metabolism. In the Na2SeO3 treatments, genes encoding phosphoglycerate mutase (PGM), triosephosphate isomerase (TPI), phosphofructokinase (PFK), pyruvate kinase (PK), malate dehydrogenase (MDH), polyamine oxidase (PAO), aspartate aminotransferase (AST), and glutathione S-transferase (GST) were upregulated, and the expression levels of differentially expressed genes (DEGs) decreased with increasing Se levels. SeMet treatments upregulated genes encoding PFK, PK, glutamine synthetase (NADH-GOGAT), and L-ascorbate peroxidase (APX), and expression levels of DEGs increased with increasing Se levels. This study provides important insights into the molecular mechanisms of the uptake and metabolism of different Se forms in rice at the seedling stage.