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

Abstract

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.