Bioscience Methods 2024, Vol.15, No.6, 289-301 http://bioscipublisher.com/index.php/bm 297 Figure 3 The metabolic route map for natural rubber (cis-1,4-polyisoprene) biosynthesis in plants, including the pathways for substrate synthesis, and their locations (Adopted from Cherian et al., 2019) Image caption: Isopentenyl pyrophosphate (IPP), the monomeric subunit for rubber biosynthesis (orange arrow) is synthesized by two pathways, the mevalonic acid pathway (MVA, cytosolic, green arrows and numerals) and the methylerythritol pathway (MEP, plastidic, red arrows and lower case letters) from acetyl-CoA or glyceraldehyde-3-phosphate and pyruvate, respectively. IPP and its stereoisomer dimethylallyl pyrophosphate (DMAPP) condense to form several allylic pyrophosphates (APPs), namely geranyl pyrophosphate (GPP, C10), farnesyl pyrophosphate (FPP, C15) and geranyl geranyl pyrophosphate (GGPP, C20). These APPs can be used as rubber chain initiators (blue arrow), FPP being the most common initiator, and are also the building blocks for terpenes such as chlorophyll, sterols, plant growth regulators, essential oils and so forth. Natural rubber biosynthesis is catalysed by rubber transferase complexes (magenta) bound to the proteolipid uni-lamella membrane (light blue) of cytosolic rubber particles, and rubber is compartmentalized to the rubber particle interior. Key: MVA enzymes: PDC, pyruvate dehydrogenase complex; AACT, acetyl coenzyme A acetyltransferase; HMGS, hydroxymethylglutaryl coenzyme A synthase; HMGR, hydroxymethylglutaryl coenzyme A reductase; MK, mevalonate kinase; PMK, phosphomevalonate kinase; MDC, diphosphomevalonate decarboxylase. MVA substrates: 1. pyruvate; 2. acetyl coenzyme A; 3. acetoacetyl coenzyme A; 4. hydroxymethylglutaryl coenzyme A; 5. mevalonate; 6. phosphomevalonate; 7. diphosphomevalonate. MEP enzymes: DXS, 1-deoxy-D-xylulose 5-phosphate synthase; DXR, 1-deoxy-D-xylulose 5-phosphate reductoisomerase; MCT, 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase; CMK,4-(cytidine 5/-diphospho)-2-C-methyl-D-erythritol kinase; MDS, 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase; HDS, 4-hydroxy-3-methylbut-2-enyl diphosphate synthase; HDR, 4-hydroxy-3-methylbut-2-enyl diphosphate reductase. MEP substrates: a+, pyruvate and D-glyceraldehyde 3-phosphate; b. 1-deoxy-D-xylulose 5-phosphate; c. 2-C-methyl-D-erythritol 4-phosphate; d. 4-(cytidine 5/-diphospho)-2-C-methyl-D-erythritol; e. 2-phospho-4-(cytidine 5/-diphospho)-2-C-methyl-D- erythritol; f. 2-C-methyl-D-erythritol 2,4-cyclodiphosphate; g. (E)-4-hydroxy-3-methylbut-2-enyl diphosphate. RP, rubber particle; RT-ase, rubber transferase complex; P, non-RT-ase rubber particle-associated proteins; complexes; PL, proteolipid unilamella membrane; NR, natural rubber polymers (Adopted from Cherian et al., 2019) 8.3 Economic impact of enhanced biosynthesis pathways Advancements in understanding and manipulating the biosynthesis pathways of rubber in both E. ulmoides and H. brasiliensis have significant economic implications. The identification of key genes and enzymes involved in rubber biosynthesis, such as the rubber elongation factor and small rubber particle protein, has opened avenues for metabolic engineering to enhance rubber yield and quality (Chow et al., 2007; Liu et al., 2018). The high-quality genome assemblies and transcriptome analyses of these species provide a robust foundation for genetic modifications aimed at increasing rubber production efficiency (Wuyun et al., 2017; Li et al., 2020). Enhanced biosynthesis pathways not only promise to boost the economic viability of EUR but also ensure a more stable and diversified supply of natural rubber, mitigating the risks associated with over-reliance on a single source (Cherian et al., 2019).
RkJQdWJsaXNoZXIy MjQ4ODYzNA==