Metabolomic dissection and biomarker identification for heat stress tolerance under ameliorative effects of methyl jasmonate in mustard (Brassica juncea L.)

Heat stress increasingly threatens productivity in mustard under late-sown agroecosystems. Here, we employed high-resolution mass spectrometry-based untargeted metabolomics to resolve metabolic reprogramming associated with methyl jasmonate (MeJA) application in the heat-susceptible genotype Pusa Bahar. Comparative profiling between timely-sown and heat-stressed late-sown conditions identified 991 and 700 metabolites, respectively, revealing extensive metabolic restructuring under stress. Multivariate and univariate analyses uncovered coordinated shifts in amino acid metabolism, lipid remodeling, carbohydrate turnover, antioxidant pathways, and secondary metabolism. OPLS-DA highlighted distinct heat-responsive metabolite signatures, including enhanced accumulation of γ-L-glutamyl-L-leucine, 2-oxoglutaric acid, cytosine, and 9-oxononanoic acid, whereas trehalose, uridine, trans-aconitic acid, and quercetin derivatives declined markedly under heat stress. MeJA treatment reinforced osmo-protection, membrane stability, and reactive oxygen species detoxification, indicating a broad metabolic adjustment to acieve stress adaptation. These findings provide metabolome-scale insights into heat resilience and identify candidate metabolic biomarkers for heat stress resilient mustard improvement in the Indian sub-continent.