## 4 Discussion
Consistent with these findings, the present study observed higher gene expression levels of genes involved in monoterpenes synthesis in _C. keiskei_. Using transcriptomic approaches, a total of 28 unique _ckTPS_ genes were successfully identified in _C. keiskei_. These _ckTPS_ genes were classified based on their amino acid length and the presence of different subfamily motif types. Through a conserved domain analysis and phylogenetic tree analysis, the _ckTPS_ genes were categorized into five TPS subfamilies (TPS-a, b, c, g and e/f) (Figure 2). Among these _ckTPS_ genes, 15 were found to be functional and responsible for the synthesis of various mono-, sesqui-, and other terpenoid compounds in _C. kieskei_. Notably, _ckTPS_9 and _ckTPS12_ in the TPS-a and TPS-b clades lacked the R(R)X\({}_{8}\)W motif, while one member of the _ckTPS16_-e/f subfamily also lacked this motif (Supplementary Figure S6). Furthermore, the sesquiterpene synthase TPS family included _ckTPS8_, which did not possess the DXXXD domain. These findings align with previous studies by [PERSON] et al. [16] and [PERSON] and [PERSON] [69], where _TPS_-related family genes lacking specific motifs or domains were identified using transcriptomic approaches. It is worth mentioning that genome-wide identification of _TPS_ genes has been reported in several land plants, including _Oryza sativa_, _A. thaliana_, _Vitis vinifera_, _Daucus carota_, _Malus domestica_, _Eucalyptus_, _Camelia sinensis_ and _Solanum lycopersicum_[14; 18; 19; 20; 21; 22; 23; 24]. In the present study, we successfully identified _TPS_-related genes in _C. kieskei_, and future investigations will deepen our understanding of the molecular mechanisms and relationships between essential oil synthesis-related genes within the genus _Convallaria_ and its closely related species. Furthermore, we identified the expression of three _ckTPS_ (_ckTPS2_, 7 and 14) and one sesquiterpene-related (_ckTPS23_) gene in all three _C. kieskei_ tissues using DEG analysis. Additionally, we performed qPCR analysis to validate our results. The qPCR analysis confirmed the high expression levels of three other _ckTPS_-related genes (_ckTPS6_, 11 and 16) in all three parts of _C. kieskei_. These genes exhibited the presence of R(R)X8W and DXXXD domains, which were also identified in sweet basil and lavender plants [70; 71]. Among these genes, _ckTPS2_ and _ckTPS23_ showed significant upregulation in the flower tissue compared to the leaf and root tissues (Figure 3). Further blast annotation of _ckTPS2_ revealed its similarity to the geraniol synthase (GES) gene, which is responsible for the sedative effects of floral odor [33]. Expression analysis showed upregulation of _ckTPS2_ in the flowers (log\({}_{2}\)FC = 4.806) and downregulation in the leaf (log\({}_{2}\)FC = \(-\)2.188) and root (log\({}_{2}\)FC = \(-\)2.618) tissues of _C. kieskei_ (Figure 4). A quantification analysis confirmed the significant expression of _ckTPS2_ in all the tissues of _C. kieskei_ (Figure 7), indicating its involvement in the synthesis of geraniol, an acyclic monoterene that contributes to floral fragrance with its light, refreshing and floral-woody-citrus notes [72]. Geraniol is abundant in flowers with distinctive structures, and finds applications in fragrances, pharmaceuticals and agrochemical industries [73]. The DEG analysis also revealed distinct log\({}_{2}\)FC values for _ckTPS23_ in the flower, leaf and root tissues, with values of +2.27, \(-\)1.27 and \(-\)2.61, respectively. Quantification studies further confirmed that _ckTPS23_ exhibited significant expression in the flowers of _C. kieskei_, while showing comparatively lower expression levels in the leaf and root tissues (Figures 6 and 7). _ckTPS23_ shares an 88% amino acid sequence identity with the _V. vinifera_-Germacrene D (Ger D) synthase gene [74]. Hence, our findings suggest the synthesis of _Ger D_ throughout the plant, as supported by the KEGG pathway analysis.