Metabolic regulation and molecular mechanism of salt stress response in salt-tolerant Astragalus mongolica

As an important medicinal plant, Astragalus mongolica has poor tolerance to high-salt environments, which limits its growth in saline-alkali areas. Studying its salt tolerance mechanism can provide a scientific basis for local adaptation, which is of great significance for improving the technical bottleneck of industrial cultivation in saline-alkali areas. This study is the first to explore the physiological responses and molecular mechanisms of two varieties of Astragalus mongolica with different salt tolerance under salt stress through the combined analysis of metabolomics and transcriptomics. The results showed that Astragalus mongolica responded to salt stress by enhancing the activity of antioxidant enzymes and the accumulation of osmotic regulating substances. The salt-tolerant varieties showed higher antioxidant capacity, inhibited the accumulation of malondialdehyde and hydrogen peroxide, and reduced the damage of oxidative free radicals, thereby improving salt resistance and promoting plant growth. Combined transcriptome and metabolome analysis revealed that under salt stress, there were 3510 differentially expressed genes and 882 differentially expressed metabolites in the leaves of the salt-tolerant variety "LQ", while there were 1632 DEGs and 797 DAMs in the sensitive variety "DT", respectively. The differentially expressed genes and metabolites were involved in metabolic pathways such as flavonoid biosynthesis, isoquinoline alkaloid synthesis, and phenylalanine metabolism. In particular, "LQ" alleviated the damage caused by salt stress and improved salt tolerance by enhancing the oxidase activity in the flavonoid and phenylalanine metabolic pathways and regulating the gene expression of key metabolites and enzymes. This study can provide important data support for the selection of suitable varieties of Mongolian Astragalus in saline-alkali areas and the breeding of excellent varieties.