Analysis of the Expression Profiles of Borneol Dehydrogenase Genes and Its Catalytic Function in Camphor Biosynthesis in Lavender

Camphor is a key quality determinant of lavender oil. Bornyl dehydrogenase (BDH) catalyzes the final camphor biosynthesis step, yet its gene family and mechanism in lavender remain uncharacterized. We phylogenetically classified 154 short-chain dehydrogenase/reductase (SDR) genes into six clades and screened 17 BDH genes. Integrated transcriptomic and metabolomic analyses revealed that camphor biosynthesis primarily occurs via the plastidic 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, with coordinated expression of geranyl diphosphate synthase (GPPS), bornyl diphosphate synthases (BPPS), bornyl-diphosphate diphosphatase (BDD), and BDH genes. Most biosynthetic genes, especially BDH and BPPS, were significantly upregulated in L. × intermedia “Xinxun 4”, correlating with its highest camphor content. Subcellular localization showed BDH1 resides in the cytoplasm, suggesting plastid-cytoplasm collaboration. In vitro assays demonstrated that BDH1 and BDH2 both oxidize (+)- and (−)-borneol to camphor. Molecular dynamics simulations revealed that BDH1’s active site exhibits conformational flexibility, accommodating both enantiomers with similar binding affinities, which was confirmed by enzyme kinetics. Asn90 was identified as a key catalytic residue. These findings reveal BDH family expansion, coordinated gene expression driving camphor accumulation, and BDH1’s catalytic flexibility, offering key genetic resources and mechanistic insights for optimizing lavender camphor content via metabolic engineering and molecular breeding.