# FhMYB108 Regulates the Expression of Linalool Synthase Gene in _Freesia hybrida_ and _Arabidopsis_
## 4 Discussion  
To optimize their chances of survival and reproductive success, plants commonly emit a substantial quantity of volatile small molecule compounds, particularly terpenoids, as chemical signaling agents to establish connections among plants or between plants and animals. These compounds play pivotal roles in essential processes such as pollination, the induction of ovulation, and even direct or indirect involvement in plant defense [40; 41; 42]. Therefore, elucidating the composition of plant volatile terpenoids is crucial for comprehending the physiological functions and potential practical applications. The release of terpenoids exhibits spatiotemporal specificity, with peak emission occurring during the period of full flower bloom or fruit ripening. The _Red River(r)_ cultivar of _F. hybrida_ at different stages of flower opening is selected as the experimental material in this study to investigate the expression pattern of the terpenoid synthase gene (_FhTPSI_), which plays a crucial role in regulating the biosynthesis of its major volatile compound (linalool). The results revealed a gradual upsurge in the expression of FhTPS1 in _F. hybrida_ during flower blooming, exhibiting a similar trend as observed in _Clarkia Breweri_[43]. The presence of this regular expression suggests the existence of a regulatory system in _F. hybrida_ that governs the expression of the linalool synthase gene, indicating an intricate mechanism for controlling secondary metabolism in this plant species. Figure 6: Interaction between FhMYB108 and AtMYC2. (**A**) The transcriptional activation assay of AtMYC2. (**B**) The expression of terpene synthase genes in AtMYC2 overexpressed _A. thaliana_. (**C**) The interaction between FhMYB108 and AtMYC2 verified by BiFC. (**D**) FhMYB108 and AtMYC2 jointly regulate the transcription of _AtTPST4_. In (**A**,**B**,**D**), data are shown as the mean \(\pm\) SD of three biological replicates. Differences were assessed using a two-tailed \(t\)-test (***, \(p\) < 0.001; ***, \(p\) < 0.01; ns, \(p\) > 0.05) in (**A**,**B**). Currently, there is a lack of a systematic approach in the investigation of transcriptional regulation mechanisms governing terpenoid biosynthesis. On one hand, the existing studies lack coherence and fail to elucidate the synergistic relationships among multiple transcription factors in a comprehensive manner. On the other hand, the majority of investigations have predominantly focused on specific cash crops such as tobacco and tomato while overlooking more significant flower plants. Among the numerous transcription factors reported, only AtMYB21 and AtMYC2 exhibit dual regulatory functions in both terpenoid metabolism and development, specifically in stamen formation, in _A. thaliana_. Previous investigations on anthocyanins and proanthocyanidins in _F. hybrida_ have underscored the potential significance of MYB transcription factors in secondary metabolism, thereby prompting our focus on elucidating the role of MYB transcription factors in linalool synthesis and regulation. By employing AtMYB21 as a bait for comparative transcriptome analysis in _F. hybrida_, we successfully identified FhMYB108, a transcription factor with the potential to regulate terpenoid metabolism. The phylogenetic grouping of FhMYB108 and AtMYB21 suggests potential functional similarities between them. Furthermore, experimental evidence derived from assays on transcription factor activation has substantiated the specific binding capability of FhMYB108 to the promoter regions of _AtTPS11_ and _AtTPS21_ (which are known targets of AtMYB21), thereby effectively inducing their transcriptional activity. Meanwhile, FhMYB108 exhibits a comparable expression pattern to _FhTPS1_ and demonstrates specific binding affinity towards the \(-916\)-\(1016\) region of the _TPS1_ promoter. Furthermore, FhMYB108 exhibits its regulatory role in the biosynthesis of monoterpene by activating the _TPS14_ gene encoding monoterpene synthase in _A. thaliana_, providing additional evidence.