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.

Ethylene response factors 2 (ERF2) are essential for plant growth, fruit ripening, metabolism, and resistance to stress.  In this study, the expression levels of the genes for MdERF2 implicated in the biosynthesis, composition and ultrastructure of fruit cuticular wax in apple (Malus domestica) were studied by the transfection of apple fruit and/or calli with MdERF2-overexpression (ERF2-OE) and MdERF2-interference (ERF2-AN) vectors.  In addition, the direct target genes of MdERF2 related to wax biosynthesis were identified using electrophoretic mobility shift assays (EMSAs) and dual-luciferase reporter (DLR) assays.  The findings indicated that the expression levels of four wax biosynthetic genes, long-chain acyl-CoA synthetase 2 (MdLACS2), eceriferum 1 (MdCER1), eceriferum 4 (MdCER4), and eceriferum 6 (MdCER6), were upregulated by ERF2-OE.  In contrast, the expression levels of these genes were inhibited when MdERF2 was silenced.  Furthermore, the overall structure and accumulation of fruit cuticular wax were influenced by the expression level of MdERF2.  Treatment with ERF2-OE significantly increased the proportions of alkanes and ketones and reduced the proportions of fatty acids and esters.  In addition, the EMSAs and DLR assays demonstrated that MdERF2 could bind directly to GCC-box elements in the promoters of MdLACS2, MdCER1, and MdCER6 to activate their transcription.  These results confirmed that MdERF2 targets the up-regulation of expression of the MdLACS2, MdCER1, and MdCER6 genes, thereby altering the composition, content, and microstructure of apple epidermal wax.