Insights into the physiological metabolism and gene regulation of Pak Choi under high temperature stress through metabolic profiling and transcriptome analyses of nano-selenium effects

• Nano-selenium enhanced the photosynthetic properties of plants by promoting the synthesis of photosynthetic pigments and repairing damage to chloroplast. • Nano-selenium enhanced the activities of antioxidant enzymes significantly, including superoxide dismutase, peroxidase, and catalase, thereby accelerating the removal of excessive reactive oxygen species in plants. • Nano-selenium regulated the expression of related genes to improve plant tolerance. The most significant KEGG pathways identified through co-enrichment analysis were glutathione metabolism, ascorbic acid metabolism, phenylalanine metabolism, and citrate cycle. In recent years, high temperature stress caused by global warming has become a significant constraint on the growth and development of pak choi ( Brassica chinensis var. pekinensis . cv. ‘Suzhouqing’). In order to explore whether nano-selenium treatment could enhance the heat resistance, three nano-selenium concentrations (H1: 2.5 mg l -1 ; H2: 5 mg l -1 ; H3:10 mg l -1 ) and a water-sprayed control group (H0) were randomly assigned with 20 mL under conditions with a light intensity of 2000 lx, a photoperiod cycle of 12 h /12 h, a temperature of 35 °C / 25 °C, a relative humidity of 80 % / 85 % in an artificial climate incubator. In this study, we conducted differential gene function analysis using the transcriptome. The results revealed significant enrichment of pathways including glutathione metabolism, biosynthesis of cofactors, biosynthesis of amino acids. Subsequently, metabolome analysis was performed to identify representative differential metabolites such as GDP- l -galactose, acetyl-CoA, toddalolactone, Gys-Gly, l -Dehydroascorbate, malate and phenylacetyl-CoA. Finally, a correlation analysis between the transcriptome and metabolome was conducted with the following results: nano-selenium enhances plant photosynthetic properties by promoting the synthesis of photosynthetic pigments and repairing chloroplast damage. Additionally, it significantly increases antioxidant enzyme activities such as superoxide dismutase, peroxidase, and catalase to accelerate the removal of excessive reactive oxygen species in plants. Furthermore, nano-selenium regulates gene expression to improve plant tolerance. The most significant KEGG pathways identified through co-enrichment analysis were glutathione metabolism, ascorbic acid metabolism, phenylalanine metabolism, and citrate cycle. In these pathways, the important genes including catalase-peroxidase, citrate synthase, malate dehydrogenase, glutathione peroxidase, isocitrate dehydrogenase, glutathione S-transferase, trypanothione synthetase, glutathione hydrolase, l -galactono-1,4-lactone dehydrogenase, glutathione dehydrogenase / transferase, l -ascorbate peroxidaseand l -galactose dehydrogenase were upregulated in the presence of nano-selenium. This study can serve as a theoretical foundation and technical guidance for utilizing nano-selenium to enhance plant resistance against high temperature stress.