Genome-wide identification and expression characteristics under stress of the Glutathione S-transferase supergene family in Leguminosae

Leguminosae play a vital role in terrestrial ecosystems and are widely cultivated for human consumption, forage production, and soil enrichment due to their nitrogen-fixing ability and nutrient-rich composition. Glutathione S-transferase (GST) constitute a widespread protein superfamily involved in toxin degradation, growth regulation, and defense against biotic and abiotic stresses. In this study, we identified 540 GST superfamily members from four representative legume species, alfalfa ( Medicago sativa ), Medicago truncatula , soybean ( Glycine max ), and peanut ( Arachis hypogaea ), at the whole-genome level, with gene numbers positively correlated with genome size and ploidy level. Phylogenetic analysis classified these members into nine subfamilies, with the Tau subfamily predominating in all species. Whole-genome duplication and segmental duplication emerged as the primary drivers of GST family expansion in legumes, while the entire superfamily evolved predominantly under purifying selection, with only the soybean-specific tandem duplicate GmGSTU18/GmGSTU19 exhibiting positive selection. Promoter regions contained 24 cis-acting elements related to growth, metabolism, and stress responses, with Tau and Phi subfamilies showing the highest element enrichment. Additionally, we systematically analyzed the expression patterns of the legume GST supergene family under various stress conditions, revealing their distinctive response mechanisms to abiotic and biotic stresses, grazing recovery, nodule formation and light induction. These findings provide a comprehensive genomic resource for legume GST genes and offer a theoretical foundation for genetic improvement of stress tolerance in leguminous crops and forages.