## 3 Discussion
In addition, _TsTPS18_ was found to be a sesquiterpene synthase, and its ectopic expression in _T. sinensis_ has been shown to promote the synthesis of \(\beta\)-caryophyllene [17]. Based on the sequence characteristics and metabolite correlation analysis, this study preliminarily identified _TsTPS1262_ and _TsTPS466_ in _T. sinensis_ as sesquiterpene synthases (Figure 5). We used transient expression systems in tobacco and _T. sinensis_ to study the function of catalyzing the production of sesquiterpenes. Our transient expression analysis showed increased copae and elemene contents (Figures 7 and 8), which is similar to results previously reported in _Arabidopsis_[23]. We found that the composition of sesquiterpenes in tobacco and _T. sinensis_ transient expression systems was different (Figures 7 and 8). This may be related to the differences in precursor substances in the recipient plants, which also indicates that the TPS genes may have broad activity on producing sesquiterpenes. is also poorly understood. In cannabis, both stalked and sessile glandular trichomes have been found. The stalked glandular trichomes are composed of 12 to 16 secretory disk cells, emit blue autofluorescence under the microscope, and are rich in cannabinoids and monoterenes; in comparison, sessile glandular trichomes are composed of 8 secretory disk cells which contain fewer cannabinoids but a higher proportion of sesquiterpenes [28]. In tomatoes, various morphologies of glandular trichomes have been observed, including multiple-stalked cells, single-stalked cells, multiple-capitate cells, and single-capitate cells [49]. The type-VI glandular trichomes, composed of multiple stalked cells and capitate cells, serve as the primary sites for the production and storage of volatile monoterenes and sesquiterpene compounds [50]. In general, regardless of the structural characteristics of glandular trichomes, most studies focus on the relationship between glandular trichome development and related secondary metabolites, especially within glandular trichomes (e.g., monoterenes, sesquiterpenes, etc.) in biosynthesis, secretion, and storage [51]. We found that glandular trichomes in _T. sinensis_ have many shapes, and the development process of sessile and stalked glandular trichomes needs further study. We still do not know whether there are differences in the types of metabolites produced by these two types of glandular trichomes, and whether the formation and development of different types of glandular trichomes are specifically regulated. Despite the significant insights gained from this study, several challenges remain. First, the isolation and characterization of trichome-specific genes in _T. sinensis_ were technically demanding due to the complexity of trichome structures and the low abundance of target transcripts. Second, the quantification of volatile compounds using GC-MS, while highly sensitive, required careful optimization to avoid artifacts and ensure reproducibility. These challenges highlight the need for more advanced techniques, such as single-cell RNA sequencing, to precisely capture trichome-specific gene expression profiles. Additionally, the integration of metabolomics and transcriptomics data could provide a more comprehensive understanding of the regulatory networks underlying volatile biosynthesis. Our work also opens new methodological perspectives for studying other woody vegetables or non-model plants. For instance, the identification of key terpene synthases in _T. sinensis_ could serve as a foundation for developing metabolic engineering strategies to enhance the production of valuable sesquiterpenes in other crops. These advancements would not only address the current limitations but also pave the way for innovative approaches in plant biology and agricultural biotechnology.