Abstract
Plants produce numerous natural products that are essential to both plant and human physiology. Recent identification of genes and enzymes involved in their biosynthesis now provides exciting opportunities to reconstruct plant natural product pathways in heterologous systems through synthetic biology. The use of plant chassis, although still in infancy, can take advantage of plant cells' inherent capacity to synthesize and store various phytochemicals. Also, large-scale plant biomass production systems, driven by photosynthetic energy production and carbon fixation, could be harnessed for industrial-scale production of natural products. However, little is known about which plants could serve as ideal hosts and how to optimize plant primary metabolism to efficiently provide precursors for the synthesis of desirable downstream natural products or specialized (secondary) metabolites. Although primary metabolism is generally assumed to be conserved, unlike the highly-diversified specialized metabolism, primary metabolic pathways and enzymes can differ between microbes and plants and also among different plants, especially at the interface between primary and specialized metabolisms. This review highlights examples of the diversity in plant primary metabolism and discusses how we can utilize these variations in plant synthetic biology. I propose that understanding the evolutionary, biochemical, genetic, and molecular bases of primary metabolic diversity could provide rational strategies for identifying suitable plant hosts and for further optimizing primary metabolism for sizable production of natural and bio-based products in plants.
Highlights
Plants produce numerous natural products that are essential to both plant and human physiology
Plant-based production of plant natural products and other biomaterials at a commercial scale may be too difficult to achieve in a short time frame (Ͻ5 years); some of the complex natural products accumulate at high levels and are being produced commercially in plants, thanks to years of cultivation and breeding [232,233,234]
Besides identifying novel specialized metabolic pathways from various plants and introducing them into a host plant (Fig. 5, green), here I emphasize the importance of optimizing plant primary metabolic pathways that provide precursors to the formation of downstream natural products and other target chemicals (Fig. 5, blue)
Summary
Plants produce diverse and often abundant chemical compounds, which play critical roles in these sessile and multicellular organisms to habitat in various environmental niches. Many of these phytochemicals are produced in a lineage-specific manner and are often referred to as specialized or secondary metabolites. Many of these plant natural products provide essential nutrients and valuable resources for the production of pharmaceuticals and biomaterials to the human society [1,2,3]. Plant chassis potentially provide promising alternative platforms to produce some of these metabolites that are difficult to produce in microbes, especially if tailored plant hosts (or chassis) are carefully selected and generated depending on downstream target compounds
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