Transcriptomic and physiological analyses reveal the effects of exogenous selenium on organic selenium synthesis and quality in tea

Camellia sinensis have significant industrial value and economic benefits. The appropriate concentration of selenium (Se) promotes C. sinensis growth. Here, we conducted a comparative analysis of the effects of selenite and nano-Se on Se/S absorption and transformation, photosynthesis, accumulation of nutritional metabolites, and antioxidant capacity in tea. Compared with selenite, nano-Se was more readily absorbed and converted into SeCys2 and SeMet. Nano-Se facilitated greater S participation in plant growth and development. 100 mg/L selenite and nano-Se treatments enhanced photosynthetic pigments, soluble sugars, soluble proteins, tea polyphenols, tea polysaccharides, and total flavonoids content in tea. Furthermore, Nano-Se treatment significantly increased antioxidant enzyme activities (GR, CAT, POD, SOD, APX), thereby enhancing tea antioxidant capacity. Transcriptome analysis revealed that, compared with selenite, nano-Se significantly upregulated the expression of genes including ABC transporters, CBSX1, GT3, GST, and MSR, which play pivotal roles in Se absorption and transformation, metabolic synthesis, and the glutathione metabolic pathway. In conclusion, nano-Se (100 mg/L) is more suitable than selenite as a low-toxicity, high-efficiency Se fertilizer for the biofortification of Se-enriched tea. These findings provide a theoretical basis for the application of Se fertilizers in improving tea quality and elucidate the molecular mechanisms by which Se regulates the growth and development of C. sinensis.