Transcriptome and physiological determination reveal the effects of selenite on the growth and selenium metabolism in mung bean sprouts

Selenium (Se) biofortification of crops has been studied to substantially improve the Se content in human dietary food intake. In the present study, Vigna radiata (mung bean) seeds were soaked in different concentrations of sodium selenite (Na₂SeO₃). Low concentration of selenite is conducive to seed germination and growth, and can increase the fresh weight (FW) and dry weight (DW) of sprouts. The concentration of Na₂SeO₃ lower than 50 mg/kg resulted in noticeable elongation in the stem and marginal elongation in root. Mung bean seeds soaked with 80 mg/kg Na₂SeO₃ accounted for 93.77% of organic Se after growing for about 5 days. Transcriptome data revealed that Se treatment enhances starch and sugar metabolism, along with the up-regulation of ribosomal protein and DNA synthesis related genes. Further analysis indicated that the mung bean seeds absorbed Na₂SeO₃ through PHT1.1 and NIP2. Se (IV) was transformed into Se (VI) and transported to stems, leaves and roots through cotyledons during the germination of bean sprouts. SULTR3;3 may play an important role in the transit process. Se (VI) or Se (IV) transported to the leaves was catalytically transformed into SeCys through SiR and CS, and SeCys is further converted to MeSeCys through SMT. Most SeCys were transformed into SeHCys through CBL, transported to plastids, and finally transformed into SeMet through Met Synthase.