Genomic Identification and Biochemical Characterization of Methyl Jasmonate (MJ)-Inducible Terpene Synthase Genes in Lettuce (Lactuca sativa L. cv. Salinas)

Terpenes are diverse plant metabolites with essential ecological and physiological functions, yet their biosynthetic regulation in lettuce (<i>Lactuca sativa</i> L.) remains poorly understood. By integrating volatile profiling, genome-wide identification, and biochemical characterization of terpene synthase (TPS) genes, we elucidated how methyl jasmonate (MJ) induces terpene formation in lettuce seedlings. Headspace analysis of 10-day-old seedlings revealed that while mock-treated tissues emitted no detectable volatiles, MJ elicitation triggered the de novo production of a terpene blend dominated by (<i>E</i>)-β-ocimene (9.3-14.6%), (<i>E</i>)-β-caryophyllene (37.2-46.9%), and caryophyllene oxide (26.2-41.4%). A genome-wide search identified 54 putative LsTPS genes, often clustered with prenyl transferases or cytochrome P450 genes. Gene expression assays revealed 17 MJ-responsive <i>LsTPS</i> genes; among them, <i>LsTPS21</i>, <i>LsTPS23</i>, <i>LsTPS28</i>, <i>LsTPS51</i>, and <i>LsTPS52</i> showed strong (>200-fold) induction, with <i>LsTPS52</i> exceeding a 20,000-fold increase. Functional characterization of six recombinant enzymes demonstrated diverse substrate specificities: LsTPS8 as an α-copaene synthase, LsTPS16 as a linalool synthase, LsTPS24 as an (<i>E</i>)-nerolidol synthase, LsTPS21 and LsTPS23 as (<i>E</i>)-β-ocimene synthases, and LsTPS10 as an (<i>E</i>)-β-caryophyllene synthase. Phylogenetic analyses confirmed conserved domains characteristic of the TPS-a and TPS-b subfamilies. This study presents the first comprehensive framework for MJ-induced terpene biosynthesis in lettuce, offering new insights into Asteraceae terpenoid metabolism.