Overexpression of the Lavender LaDXS2-2 Gene in Tobacco Modulates the MEP Pathway to Improve Photosynthetic Efficiency and Alter Primary Metabolism: Evidence from Integrated Omics Analyses

1-Deoxy-D-xylulose-5-phosphate synthase (DXS) serves as the initial rate-limiting enzyme in the methylerythritol phosphate (MEP) pathway, governing the biosynthesis of precursors for photosynthetic pigments and terpenoids. In this study, the LaDXS2-2 gene was cloned and functionally characterized in lavender (Lavandula angustifolia). The full-length coding sequence (CDS) of LaDXS2-2 spans 2178 base pairs, encoding a protein of 725 amino acids. Phylogenetic analysis revealed that LaDXS2-2 is most closely related to the DXS from Salvia miltiorrhiza. Expression profiling demonstrated that LaDXS2-2 was highly expressed in flower buds, and its transcript levels were significantly upregulated (p < 0.05) in response to ethephon, high light intensity, and low temperature, while exhibiting tissue-specific responses to gibberellin application. Subcellular localization assays confirmed LaDXS2-2 is targeted to the chloroplast. Heterologous overexpression of LaDXS2-2 in tobacco resulted in a marked increase in photosynthetic pigment content, enhanced the actual photochemical efficiency of photosystem II [Y(II)], and reduced non-photochemical quenching (NPQ). Integrated transcriptomic and metabolomic analyses further revealed that LaDXS2-2 overexpression activated the diterpenoid biosynthesis pathway and upregulated amino acid metabolism as well as the TCA cycle, while competitively suppressing phenylpropanoid and flavonoid biosynthesis pathways. These findings indicate that LaDXS2-2 not only enhances photosynthetic efficiency by promoting the synthesis of photosynthetic pigments but also suggests a potential role in influencing primary carbon and nitrogen metabolism, as inferred from transcriptomic and metabolomic data. This functionality may ultimately influence plant growth and metabolic homeostasis. Overall, this study provides a theoretical foundation for the synergistic improvement of photosynthetic efficiency and secondary metabolism in crops.