Mevalonate and Methylerythritol Phosphate Pathways: Terpenoids and Steroids

Terpenes are naturally occurring metabolites with structural diversity based on the number of isoprene units (C5H8). They are biosynthesized following mevalonate (MVA) or methylerythritol phosphate (MEP) pathways. The MVA pathway occurs in the cytosol in plants to form sesquiterpenes (C15) and triterpenes (C30). The MEP pathway occurs in the plastids in plants to form monoterpenes (C10), diterpenes (C20) and tetraterpenes (C40). Depending on the structure, metabolites belonging to this group are essential for plants to interact with the environment for example, protecting plants against herbivores and pathogens and attracting pollinators. Some metabolites are involved in respiration (ubiquinone) and photosynthesis (chlorophylls, carotenoids, phylloquinones, and plastoquinone). Some of the metabolites are growth regulators (brassinosteroids, gibberellins, and strigolactones), and present as part of the membrane structure (sterols). They are also sources of flavours and fragrances (monoterpenes and sesquiterpenes), medicine (taxol for cancer, artemisinin for malaria), and commercial materials (rubber and gutta-percha).