## 3 Discussion
A MeJA response element was found in the promoter sequence of the _CbWRKY24_ gene of _Ursula bile_, which responds to MeJA induction. In overexpressed plants, it was found that the expression levels of genes such as _HMGR_, _FPS_, _SE_, and _\(\beta\)-AS_ were significantly upregulated, thereby improving the total saponin content of bear bile grass [44]. Treatment of _Panax notoginseng_ with three plant elicitors (JA, ABA, and SA) can upregulate the expression levels of the key genes _PgFPS_ and _PgIPPI_ for terpenoid synthesis, promote the synthesis of triterpen compounds, and promote the accumulation of triterpenoid saponins [45]. Gene expression analysis of _M. recutitta_ revealed that _MrFPS_ was significantly upregulated in response to methyl jasmonate. The expression patterns varied considerably among different plant tissues, with the highest expression levels observed in flowers and stems. This tissue-specific distribution implies that different plant sections have distinct roles for the FPS enzyme in the production of secondary metabolites [18]. _CnFPPS_ expression was consistently observed across various tissues in _C. mobile_, with the highest concentrations found in the root system. This distribution pattern indicated that _CnFPPS_ may play a key role in regulating terpenoid production [20]. Functional analyses of _AvFPS_ revealed that _Aconitum vilmorinianum_ was significantly upregulated in response to methyl jasmonate. Moreover, genetically modified expression of _AvFPS_ increased the plant's resistance to environmental stressors, which increases its ability to be cultivated under less ideal circumstances [46]. In summary, plant hormones affect the biosynthesis and accumulation of triterpenoid compounds by affecting key enzyme activities, differential expression of key enzyme genes, regulation of transcription factors and promoter activities, and synergistic interactions between plant hormones [32]. In this study, a large number of cis-elements (ABRE, TCA-element, CGTCA-motif, and TGACG-motif) that responded to the plant hormones ABA, SA, and MeJA were also found in the promoters of _E. hirta FPS_ genes. Through exogenous JA and SA treatments, we further investigated the expression patterns of _EhFPS_ genes under SA and JA signaling. It was found that, except for _EhFPS5_, all other genes responded to SA treatment, exhibiting significant upregulation of expression. The expression trends of _EhFPS_ genes could be divided into three subgroups, with _EhFPS1, EhFPS2_, and _EhFPS7_ showing similar expression patterns, whereas _EhFPS3, EhFPS4_, and _EhFPS8_ displayed a consistent trend. This is consistent with the known relationship between terpenoid biosynthesis and hormone signaling in plants. Under exogenous JA treatment, genes such as _EhFPS1, EhFPS2, EhFPS6, EhFPS7_, and _EhFPS8_ rapidly responded to JA signals, showing a significant increase in expression levels. We also observed that some genes, such as _EhFPS1, EhFPS2_, and _EhFPS7_, responded quickly to both SA and JA signals, demonstrating expression patterns similar to those of terpenoid synthases under various stress conditions, as reported in the literature [39]. This result is also consistent with our findings from cis-acting element analysis of the promoters. These experiments further support the hypothesis that these genes play a key role in terpenoid biosynthesis. Therefore, it is speculated that terpenoid compounds are mainly synthesized in the latex and leaves. Terpenoids are widely present in nature and constitute the main components of essences, resins, and pigments in some plants [47]. Tissue-specific expression analysis revealed that _EhFPS1, EhFPS2_, and _EhFPS7_ exhibited significantly higher expression levels in the latex of _E. Hirta_ than the other genes, suggesting that these genes may be involved in the regulatory pathway of latex synthesis. This finding was consistent with our hypothesis regarding terpenoid biosynthesis.