Transcriptomic responses of mint to sodium selenite treatment

Selenium (Se) is a beneficial micronutrient that, at optimal concentrations, supports plant growth, stress resistance, and secondary metabolism. However, its regulatory effects are highly dose-dependent. This study investigated the physiological, transcriptomic, and metabolomic responses of peppermint (Mentha piperita L.) to foliar application of sodium selenite (Na2SeO3) at concentrations ranging from 0 to 100 mg/L. Treatment with 30 mg/L Na2SeO3 (Se30) significantly enhanced plant growth, photosynthetic efficiency (Pn +28.19%, ETR +31.11%, Fv/Fm +10.42%), and antioxidant enzyme activities (POD +38.47%, SOD +34.14%, CAT +22.53%, APX +41.27%), while reducing oxidative stress markers (MDA -43.55%, H2O2 -37.52%). In contrast, high concentrations (e.g., 60 mg/L, Se60) suppressed growth, caused chloroplast ultrastructure damage, decreased photosynthetic efficiency, and induced oxidative stress. Transcriptomic analysis revealed that Se30 upregulated genes involved in selenium metabolism (e.g., MenB, CS, HMT), redox homeostasis (e.g., GPX, GR), secondary metabolism (e.g., PAL, 4CL), and hormone signaling (e.g., AUX1, ARFGEF), whereas Se60 led to widespread downregulation of growth-related and metabolic genes. Metabolomic profiling confirmed increased accumulation of flavonoids (e.g., vitexin, neohesperidin), amino acids, and phenolic acids under Se30, while Se60 inhibited these pathways. Mint tea from Se30-treated plants had higher amino acid content (+29.74%), enhanced sweetness, and reduced bitterness, whereas Se60 negatively affected flavor compounds such as luteolin and salvianolic acid. These findings elucidate the dual role of selenium in modulating peppermint growth and quality and provide a mechanistic basis for optimizing selenium biofortification in medicinal and edible plants.