Metabolomics reveals signature metabolites associated with high-oiliness flue-cured tobacco (Nicotiana tabacum L.) leaves.

BACKGROUND: High oiliness is a crucial trait evaluated in flue-cured tobacco (Nicotiana tabacum L.) after the curing process, determining its visual appeal and industrial usability. However, its specific metabolic characteristics and objective evaluation markers remain unclear. METHODS: In this study, widely targeted metabolomics and conventional chemical analyses were integrated to systematically profile flue-cured leaves with varying oiliness levels. Results: We identified robust candidate biomarker panels--comprising 20 and 21 characteristic metabolites for middle and upper leaves, respectively--that effectively distinguish the high-oiliness phenotype. Interestingly, our results revealed distinct positional differences in the metabolic signatures associated with high oiliness. In middle leaves, high oiliness was predominantly characterized by elevated soluble sugars and a significant enrichment of phenylpropanoid-derived aroma precursors (e.g., coniferin and syringin), alongside a concomitant accumulation of chloride. Conversely, high-oiliness upper leaves exhibited a distinct signature of lipid remodeling and oxylipin accumulation represented by 9-OxoODE and 12-oxo-PDA; these metabolites were significantly negatively correlated with starch content. Receiver operating characteristic (ROC) analysis validated the high classification accuracy of these candidate biomarkers. CONCLUSION: Although further mechanistic validation is required, this study elucidates the complex metabolic profiles of high-oiliness tobacco leaves, providing an objective biochemical evaluation framework and molecular candidate targets for standardized post-curing tobacco grading and precision breeding of high-oiliness varieties.