Floral scent is an important ornamental trait in garden plants. Monoterpenes, a major class of terpenoids, constitute the primary volatile components of lily floral scents. 1-Deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) catalyzes the second enzymatic step in the MEP pathway, which supplies precursors for monoterpene biosynthesis. However, the functional role of the DXR gene in floral monoterpene production in Lilium Oriental Hybrid ‘Sorbonne’ remains unclear. In this study, ‘Sorbonne’ was used as the experimental material, and a differentially expressed LiDXR gene was identified from early transcriptomic data, showing high temporal correlation with the synthesis and emission dynamics of floral volatiles during flowering. The LiDXR gene was cloned and subjected to bioinformatics analysis, revealing that it encodes a protein of 472 amino acids. LiDXR expression peaked at the half-open floral stage and was significantly higher in petals than in other floral organs. Subcellular localization analysis indicated that the LiDXR protein is targeted to chloroplasts in leaf epidermal cells. VIGS of LiDXR reduced monoterpene levels by downregulating the expression of downstream TPS genes in the MEP pathway. Consistently, headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) revealed a significant decrease in total volatile terpene content in silenced lilies. Transgenic Arabidopsis thaliana and petunia plants overexpressing LiDXR exhibited enhanced growth vigor and accelerated flowering. GC-Murashige and Skoog’s (MS) analysis of transgenic petunias showed a 78% increase in total volatile terpenes compared to wild-type plants. Overexpression of LiDXR also modulated the expression of other MEP pathway genes, thereby influencing the biosynthesis of downstream terpenoids, including monoterpenes. This study elucidates the functional role of LiDXR in terpenoid metabolism and provides a theoretical foundation for floral scent breeding in lily and other ornamental plants.
