## 2 Biosynthesis and Key Regulatory Networks of Volatile Terpenoids
### Regulatory Determinants of Volatile terpenoid Biosynthesis
#### 2.2.3 Plant Hormones  
Plant hormones coordinate the dynamic reprogramming of secondary metabolism during development, defense priming, and environmental adaptation via complex signaling networks. Key phytohormones such as jasmonic acid (JA), salicylic acid (SA), ethylene (ET),and abscisic acid (ABA) activate specific TFs to regulate the expression of TPS genes, thereby modulating the biosynthesis and emission of VTs, including monoterenes, sesquiterpenes, and diterpenes. This hormonal integration ensures precise spatiotemporal regulation of floral scent emission and stress-induced volatile signaling, which are critical for plant ecological fitness.  
JA plays a central role in regulating terpenoid biosynthesis by integrating into both the MVA and MEP pathways. JA directly modulates the expression of key biosynthetic genes, including _DXS_, _DXR_, _PMK_, and _TPS_, while indirectly coordinating TFs such as the MYB, bHLH, and WRKY families to fine-tune terpenoid production [84]. The JA signaling module consists of the F-box protein COI1, JAZ transcriptional repressors, and the central transcription factor MYC2. Upon JA accumulation, COI1, together with bioactive jasmonoyl-isooleucine (JA-Ile), facilitates the assembly of the SCFCOI1 E3 ubiquitin ligase complex, which specifically interacts with JAZ repressors. This interaction triggers JAZ ubiquitination and subsequent proteasomal degradation, thereby releasing MYC2 [85; 86] to promote the biosynthesis of terpenoid metabolites. Functional studies in _Fragaria \(\times\) ananassa_ show that JA treatment induces the expression of _FaTPS1_, which catalyzes the synthesis of germacrene D, with _FaMYC2_ acting as the JA-responsive TF driving this regulatory cascade [87]. Similarly, exogenous methyl jasmonate (MeJA) application in _Solanum lycopersicum_ upregulates the terpene synthase gene _Sl|IG_, enhancing sesquiterpene biosynthesis and conferring insect resistance through volatile-mediated defense mechanisms, thereby illustrating the evolutionary conservation of JA-mediated terpenoid regulation across plant species [88].  
ET, a gaseous phytohormone, regulates plant growth, developmental transitions, and responses to environmental stress through intricate signaling networks [89]. In grapevine (_Vitis viinfera_), the ET-responsive transcription factor _VviERF003_ upregulates _VviGT14_, enhancing the biosynthesis of glycosylated monoterenes [90]. Notably, ET acts upstream of JA and SA signaling while functioning downstream of nitric oxide (NO) and hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) pathways, serving as a key mediator in endophytic fungus-induced sesquiterpenoid production in _Attractylodes lancea_[91].  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Transcription** & **Gene** & **Species** & **Regulatory Substance** & **Reference** \\
**Factor** & **Name** & **Name** & **Name** & **I**nhibits limonene and & [92] \\ \hline \multirow{8}{*}{MYB} & _MsMYB_ & _Mentha spicata_ & & & \\  & _AlMYB59_ & _Attractylodes lancea_ & & & \\  & _FhMYB21L1_, & & & & \\  & _FhMYB21L2_ & & & & \\  & _FhMYB108_ & _Lilium_ & & & \\  & _AmMYB24_ & _Antirrhinum majus_ & & & \\  & _JsMYB108_, & & & & \\  & _JsMYB305_ & & _Jasminum sambac_ & & \\  & _MYB_ & _Saussurea lappa_ & & & \\  & _HcMYB1_, & & & & \\  & _HcMYB21_ & & & & \\  & _HcMYB22_ & & & & \\  & _SIMYB75_ & _Solanum lycopersicum_ L. & & & \\  & _HcMYB_ & _Hedychium coronarium_ & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Involvement of transcription factors in the biosynthesis of plant volatile terpenoids.