# FhMYB108 Regulates the Expression of Linalool Synthase Gene in _Freesia hybrida_ and _Arabidopsis_
## 1 Introduction  
Floral fragrances are secondary metabolites that are gradually secreted by odor glands in natural plants, characterized by low molecular weight, polarity, boiling point, and high fat solubility [1]. Floral fragrance, acting as a blend of naturally synthesized compounds from multiple plants in their principal habitats, exhibits significant biological functions including disease and pest resistance, as well as the attraction of insect pollinators [2]. Specific floral constituents, such as linalool, possess potent aromatic properties and find extensive applications in various fields including cosmetics, perfumery, culinary spices, and food additives [3, 4, 5, 6]. Concurrently, a diverse array of floral constituents, such as linalool and geraniol, exhibit a broad spectrum of biological activities encompassing antibacterial, anti-inflammatory, anticancer, and antidepressant properties among others. Consequently, their application is widely prevalent in the pharmaceutical field [7; 8; 9; 10]. Currently, over 1700 plant components have been identified as constituents of floral fragrances, primarily categorized into terpenoids, benzene rings/phenylpropanoids, and aliphatic derivatives [11; 12]. Among these substances, terpenoids emerge as the predominant constituents of floral volatiles [13]. The biosynthesis of terpenoids is intricately regulated by plants throughout their growth and development, circadian rhythm, and tissue specificity [14; 15; 16; 17; 18]. The synthesis of these compounds occurs in specific plant tissues and their release into the environment is tightly regulated during precise developmental or growth stages. For example, certain plant species exhibit nocturnal flowers that emit abundant volatiles, thereby adapting to the behavior of nocturnal insects; this specific synthesis and release mechanism facilitates the enhanced adaptation of the plant to its ecological niche [19]. Terpenoid synthases, strategically positioned at the key junctures of terpenoid synthesis metabolism, possess the enzymatic capability to catalyze the conversion of FPP or GPP into a diverse repertoire encompassing monoterpenes, sesquiterpenes, and other associated compounds [20; 21]. The synthesis and release of terpenoids often exhibit a positive correlation with the transcriptional levels of their corresponding terpenoid synthase genes [22]. The predominant volatile compound in _A. thaliana_ is caryophyllene, accounting for approximately 90% of the total volatiles. To date, a total of 32 terpenoid synthase genes have been successfully cloned from _A. thaliana_, with _TPS11_ and _TPS21_ exhibiting significant expression levels and widespread involvement in the biosynthesis of caryophyllene and specific sesquiterpenes. Similarly, the production of specific volatile monoterpenes can also be attributed to several individuals, including TPS2, TPS3, TPS14, and TPS23 [23]. The release of linalool and meridold exhibits a positive correlation with the expression of corresponding _TPS_ genes in _Snapdragons_[24]. Additionally, the _HCTPS2_ gene in white ginger exhibits exclusive and specific expression solely within floral organs [25]. Therefore, it can be inferred that terpene synthase plays a pivotal role in the biosynthesis of terpenoids and serves as a crucial determinant of floral composition. Currently, the transcriptional regulation of plant volatile terpenoids involves a repertoire of eight distinct types of transcription factors, including AP2/ERF, WRKY, NAC, bZIP, SRS, SBP, MYB, and bHLH family member [26]. In _A. thaliana_, AtMYB21 and AtMYB24 exhibit the positive regulation of flower development, wherein the expression levels of _AtTPS11_ and _AtTPS21_ gradually increase during flower development to facilitate the release of sesquiterpene cyanophyllene [27; 28; 29].