## 4 Discussion  
This study analyzed 16 potential agarwood-inducing fungal strains. Samples treated with these strains contained terpenids resembling characteristic agarwood components: (-)-\(\beta\)-elemene, \(\beta\)-eudesmol, alloaromadendrene, camphor, humulene, naphthalene, and 1-tetradecene. _Fusarium solani, Penicillin chrysogenum, Fusarium equiseti_, and _Phaeoarcmonium alvesi_ exhibited elevated agarotetrol levels. Quantifying alcohol-soluble extracts, 2-(2-phenylethyl) chromones, and other biomarkers could validate their efficacy as dominant induction strains. _Nadezhdiella cantori_ larvae demonstrated ideal biotic induction by forming feeding galleries within _A. sinensis_ xylem. Although termites are documented consumers of _A. sinensis_, their exclusion was necessitated by obligate eusociality requiring intact colonies for survival, coupled with destructive feeding behavior that causes structural collapse when tree defenses are compromised. When _A. sinensis_ experiences physical/chemical/fungal stress, it activates defense responses producing antibacterial sesquiterpenes and chromones [41]. Prior transcriptomics identified 26 sesquiterpene biosynthetic genes in mechanically injured xylem [42]. Our study revealed that April treatments induced significant transcriptional reprogramming with consistent pathway enrichment versus BMZ controls; upregulated genes in isoflavenoid/flavonoid/sesquietrepenoid biosynthesis potentially drive sesquiterpene production, while downregulated photosynthesis/light-harvesting/circadian genes reflect adaptive stress responses [43, 44]. This dynamic equilibrium enhances stress tolerance during agarwood formation [45, 46, 47, 48]. Sesquietrepene biosynthesis correlated positively with MVA/MEP pathway enzymes and terpene synthases (TPS), particularly under fungal-insect co-induction (cjYB1Z4), suggesting enhanced sesquiterpenoid production and positioning this treatment as a key research model. Figure 17: Differential unigene co-expression network. Note: Genes involved in sesquiterpene biosynthesis are represented by circles, and transcription factors are represented by triangles. Transcriptional regulation [49] of sesquiterpenoid biosynthesis involves AP2/ERF, WRKY, bZIP, and bHLH families [50; 51; 52; 53]. bHLH member MYC directly activates _TPS_ promoters [54], consistent with our observed bHLH upregulation. AP2/ERF and bZIP regulate terpenoid genes across plants [55; 56; 57], exemplified by ORCA3-mediated _DXS_ activation in _Catharanthus roseus_[57]. WRKY proteins modulate stress responses and sesquiterpenoid synthesis, as shown by _GaWRKY1_ activation and _WRKY44_ repression of _TPS_ promoters [52]. Our co-expression network indicates WRKY/AP2/bHLH/bZIP families exert dual (positive/negative) regulation on sesquiterpenoid biosynthesis, with _WRKY33_, _ABF_, and _WRKY2_ showing high connectivity to synthase genes, suggesting pivotal regulatory roles requiring functional validation. In conclusion, we propose that _A. sinensis_ rapidly activates a protective mechanism upon injury by secreting resin containing compounds like sesquiterpenes and chromones. Under the dual 'insect infestation + fungal invasion' induction mode, genes associated with sesquiterpene and chromone biosynthesis exhibit significant upregulation, accelerating this process. Simultaneously, insect-bored tree tissues facilitate biochemical interactions between fungi and resin, triggering biochemical reactions that gradually transform resin into aromatic constituents (e.g., agarotetrol). This dual biological induction mechanism promotes agarwood formation and endows the product with distinctive aroma and medicinal properties. Our study addresses oversimplified induction methods by elucidating treatment-specific effects on agarwood formation.