## 2 Biosynthesis and Key Regulatory Networks of Volatile Terpenoids
### Regulatory Determinants of Volatile terpenoid Biosynthesis
#### 2.2.2 Transcription Factors  
Transcription factors (TFs) are sequence-specific DNA-binding proteins that regulate transcriptional initiation by targeting cis-regulatory elements, thereby modulating the expression of structural genes essential for plant developmental processes and specialized metabolic pathways [60; 61]. In recent years, multiple TF families have been identified as direct or indirect regulators of VT biosynthetic pathways at the transcriptional level. These transcription factors can coordinately activate gene clusters within specific metabolic modules, significantly enhancing flux efficiency through these pathways. Among the key TF families implicated in VT regulation are AP2/ERF, WRKY, bHLH, bZIP, zinc-finger, MYB, and NAC families, which exert combinatorial control over terpenoid biosynthesis [62; 63]. To provide a more systematic overview of the transcriptional regulation of plant terpenoid metabolism, we summarize a set of representative transcription factors that have been functionally validated in different plant species and are involved in the regulation of volatile monoterpene and sesquiterpene biosynthesis (Table 1). Most members of these transcription factor families act as positive regulators, while the MYB and bHLH families exhibit functional diversity, functioning either as activators or repressors depending on their target genes and expression contexts. Notably, some transcription factors show organ- or species-specific expression patterns, further reflecting the spatiotemporal complexity of terpenoid metabolic regulation. Overall, the transcriptional control of volatile terpenoid biosynthesis in plants is highly complex and modular, and many potential regulators and their underlying mechanisms remain to be fully elucidated. MYB TFs, one of the largest transcription factor families in plants [64], predominantly regulate VT biosynthesis by modulating the transcription of core structural genes. In sweet osmathus (_Osmanthus fragrans_), functional characterization of _OfMYB1R114_ and _OfMYB1R70_ revealed their roles in promoting \(\beta\)-ionone biosynthesis, whereas _OfMYB1R201_ functions as a repressor, inhibiting \(\beta\)-ionone production [65]. In tomato (_Solanum lycopersicum_), _SIMYB75_ enhances anthocyanin accumulbiosynthesis of volatile aroma compounds in fruits. Overexpression of _SIMYB75_ activates the promoters of lipoxygenase C (_LOXC_), aromatic amino acid decarboxylase 2 (_AADC2_), and _TPS_ genes, thereby boosting the production of diverse aromatic volatiles, including aldehydes, phenylpropanol derivatives, and terpenoid volatiles [66]. A dual regulatory mechanism governing glandular trichome development and diterpenoid biosynthesis was elucidated in _Cenyza blini_. Transient overexpression or RNA interference (RNAi)-mediated silencing of _CbMYB108_ in leaves respectively increased or decreased diterpenoid accumulation and peltate glandular trichome density. Mechanistically, _CbMYB108_ upregulates the expression of 1-deoxy-D-xylulose 5-phosphate synthase (_CbDX5_) and geranylgeranyl diphosphate synthase (_CbGGPPS_) in the diterpenoid biosynthetic pathway [67]. In _Lilium 'Siberia'_, transient silencing of _LiMYB305_ in petals significantly downregulated the expression of monoterpene biosynthesis-related genes _LiOcS_ and _LiMyS_, leading to a marked reduction in the emissions of linalool, ocimene, and mycrene. This functional analysis unequivocally establishes _LiMYB305_ as a master transcriptional regulator of monoterpene biosynthetic pathways [68]. MYC TFs, belonging to the bHLH family, have been identified and functionally characterized in multiple plant species, including _Arabidopsis thaliana_[69; 70], _Solanum lycopersicum_[71], _Artemisia annua_[72], and _Camelia sinensis_[73], where they primarily regulate monoterpene and sesquiterpene biosynthesis. In wintersweet (_Clinnonanthus praccox L_.