Sesquiterpenoids in Agarwood: Composition, biosynthesis, and metabolic regulation

Agarwood, a highly prized aromatic wood, is renowned for its rich and complex fragrance and serves as a key raw material in incense production and high-end fragrance applications. Its distinctive scent is primarily attributed to sesquiterpenoids and 2-(2-phenylethyl) chromones. Sesquiterpenoids, which are C 15 secondary metabolites made up of three isoprene units, represent a major class of volatile compounds in Aquilaria species. Based on structural diversity, these compounds can be classified into eight major types, each contributing uniquely to agarwood’s characteristic aroma. The biosynthesis of sesquiterpenoids in Aquilaria predominantly occurs via the cytoplasmic mevalonate (MVA) pathway. This pathway proceeds in three key stages: (1) formation of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP); (2) synthesis of farnesyl diphosphate (FPP), the direct precursor of sesquiterpenoids; (3) cyclization and structural diversification catalyzed by sesquiterpene synthases, the key enzymes regulating carbon flux into sesquiterpenoid end products. Research indicates that sesquiterpenoid metabolism in Aquilaria is influenced by various factors, including hormones, transcription factors, physical injury and microbial invasion. This review summarizes current knowledge on the composition, biosynthesis and metabolic regulation of sesquiterpenoids in Agarwood, providing a foundational framework for future mechanistic studies and biotechnological applications aimed at enhancing agarwood production. • Clarify the structure of sesquiterpenoids in agarwood and their contribution to aroma. • Summarize the key enzymes in the biosynthetic pathway of sesquiterpenoids in agarwood. • Summarize the metabolic regulatory network of sesquiterpenoids in agarwood.