Integrative metabolomics and transcriptomics profiling reveals enhanced aroma precursor biosynthesis in tobacco leaves at the mature harvest stage

Tobacco is an important economic crop grown primarily for its leaves, and the quality of flue-cured tobacco is strongly influenced by harvest maturity. To accurately determine the optimal harvest maturity of flue-cured tobacco leaves, this study examined the maturity of ‘Yunyan 87’ tobacco leaves across various harvest periods in Chongqing region. Our findings revealed that mature tobacco leaves enhanced both the appearance quality and the coordination of chemical composition in flue-cured tobacco. Metabolomics analysis showed that mature tobacco leaves had the highest levels of glucose, fructose, sucrose, and other sugars, while the flavonoid content was highest in over-mature leaves, and lowest in immature leaves. Transcriptomics analysis indicated that the gene expression pattern in mature tobacco leaves significantly differed from that in immature and over-mature leaves. DEGs were predominantly enriched in pathways associated with sugar, amino acid, and phenylpropanoid metabolism. The correlation analysis with metabolomics showed that compared with immature and over-mature tobacco leaves, mature tobacco leaves were more conducive to the accumulation of amino acids and the decrease of nicotine content. This experiment revealed the dynamic changes of aroma precursors and the potential mechanism of related genes in the key stages of curing of tobacco leaves with different maturity, and provided a valuable reference for the selection of suitable curing period for tobacco.