Integrated transcriptomic and metabolomic identification of the core pathway of photosynthetic carbon fixation in mung bean under saline-alkali stress

Mungbean ( Vigna radiata L.), an important grain legume crop, suffers severe constraints in growth and yield under saline-alkali stress. However, research on the molecular mechanisms underlying stress responses remains limited, and the identification of key genes conferring saline-alkali tolerance is still in its exploratory stages. In this study, saline-alkali-tolerant material(JG)and saline-alkali-sensitive material(TQ)were subjected to 100 mmol·L - ¹ mixed saline-alkali stress, with samples collected at 0, 3, and 7 treatment stages for analysis, and it was found that there were significant genotypic differences in superoxide dismutase activity and proline content after the treatment, while obvious differences in malondialdehyde content and soluble sugar content were observed in the same genotype before and after the treatment. Transcriptomic results revealed that the number of differentially expressed genes (DEGs) in each comparison group ranged from 1,833 to 7,886. A total of 42 differentially expressed transcription factors associated with saline-alkali stress responses were identified, and these transcription factors exhibited more pronounced stress-responsive expression patterns in the JG genotype. Weighted gene co-expression network analysis (WGCNA) was performed on the DEGs, which led to the screening of four core modules. The hub genes were further validated via quantitative real-time polymerase chain reaction (qRT-PCR), and the validation results were consistent with those of the transcriptomic sequencing. Notably, the hub genes involved in pyruvate metabolism and glyoxylate and dicarboxylate metabolism were upregulated with the prolongation of stress duration. Metabolomic analysis detected a total of 5,905 metabolites, and KEGG pathway annotation showed that the arginine and proline metabolism pathway was significantly enriched in all comparison groups. D-Arginine, D-Ornithine, L-Asparagine, spermine and nicotinamide riboside were identified as the key metabolites of mungbean in response to saline-alkali stress. Transcriptomic and metabolomic datasets were co-enriched in the carbon fixation in photosynthetic organisms pathway, where 18 DEGs were found to have regulatory or interactive relationships with key metabolites. Among these genes, LOC106754509 and LOC106772717 , which encode fructose-1,6-bisphosphatase, were both downregulated in the two genotypes after stress treatment, while LOC106754931 , encoding aspartate aminotransferase, was upregulated in both genotypes. In addition, pyruvate content showed an opposite changing trend in the two genotypes. These findings provide important genetic resources and metabolomic data for an in-depth elucidation of the molecular regulatory mechanisms underlying saline-alkali tolerance in mungbean, clarify the key pathways of synergistic regulation between the transcriptome and metabolome, and lay a solid theoretical foundation for subsequent genetic improvement and molecular breeding of saline-alkali-tolerant mungbean.