Integrated transcriptomics and metabolomics reveal key metabolic pathway responses in Mentha Piperita L. under selenite stress.

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 aims to investigate how varying concentrations of sodium selenite (Na(2)SeO(3)) affect the physiological, transcriptomic, and metabolomic responses of peppermint (Mentha piperita L.). Specifically, we hypothesize that low doses promoting beneficial effects and high doses inducing toxicity. Our results demonstrate that treatment with 30 mg/L Na(2)SeO(3) (Se30) significantly enhanced plant growth, photosynthetic efficiency, and antioxidant enzyme activities and secondary metabolite production, including flavonoids. In contrast, 60 mg/L Na(2)SeO(3) (Se60) suppressed growth, caused chloroplast ultrastructure damage, decreased photosynthetic efficiency, and induced oxidative stress. Transcriptome analysis identified a total of 1047 differentially expressed genes across the comparisons between Se30, Se60, and CK. Metabolomic analysis showed that Se stress affected four metabolic pathways, involving 124 differentially expressed metabolites, mainly including tyrosine metabolism, flavonoid and phenylpropanoid biosynthesis, and ABC transporters. Transcriptomic and metabolomic analyses revealed that Se30 upregulated genes involved in sucrose metabolism, biosynthesis of glutathione and phenylpropanoids, tryptophan metabolism, hormone signaling and selenium assimilation. Additionally, low-dose foliar Na(2)SeO(3) enhances phenolic accumulation and amino acid content, thereby improving both the nutritional and sensory attributes of peppermint. 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.