Biosynthesis of Essential Oil in Aromatic Plant Species: A review

Essential oils (EOs) are complex mixtures of volatile secondary metabolites synthesized in aromatic plants, valued for their therapeutic, aromatic, and industrial applications. This review provides a comprehensive analysis of the biosynthetic pathways involved in essential oil production, emphasizing the enzymatic and genetic regulation underlying terpenoid formation. Essential oils are primarily derived from two distinct metabolic pathways: the cytosolic mevalonate (MVA) pathway and the plastidic methylerythritol phosphate (MEP) pathway. Both pathways produce the universal precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), which serve as the foundation for terpenoid biosynthesis. Terpene synthases (TPS) catalyze the conversion of these precursors into diverse terpenoids, including monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), and higher-order terpenes, each contributing to the characteristic fragrance and biological activity of essential oils. The commercial significance of essential oils is immense, with applications spanning pharmaceuticals, cosmetics, food flavoring, and aromatherapy. The global market for essential oils is projected to grow from USD 10.3 billion in 2021 to USD 18.25 billion by 2028, driven by increasing demand for natural and organic products. However, optimizing EO production requires deeper insights into metabolic engineering, environmental influences on biosynthesis, and genetic manipulation of key enzymatic steps. This review consolidates current knowledge on terpenoid biosynthesis, discusses the roles of critical enzymes and genes, and highlights future research directions to enhance EO yield and diversification. Understanding these mechanisms will facilitate the development of sustainable strategies for industrial-scale essential oil production.