Overview of trans -polyisoprene biosynthesis pathway in plants. In the isoprenoid biosynthetic pathway, the basic five-carbon unit IPP is synthesized in the cytoplasm via the MVA pathway or in plastids via the DXP pathway. Then, IPP is interconverted to its highly electrophilic isomer, DMAPP, by the isomerase IPI at the first step. DMAPP then loses its inorganic pyrophosphate to form isoprene, which sequentially condenses with IPP to generate the short-chain isoprenoid precursors GPP, FPP, and GGPP. These precursors are further metabolized for the biosynthesis of distinct sets of isoprenoids, such as monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), and polyisoprenes (C>5000) by various isoprenyl diphosphate synthases.