Rapid Communication - International Research Journal of Plant Science ( 2024) Volume 15, Issue 3
Published: 28-Jun-2024, DOI: http:/dx.doi.org/10.14303/irjps.2024.23
Plants, as autotrophic organisms, are masters of chemical synthesis. Through complex metabolic networks known as synthetic pathways, they produce an array of organic compounds essential for growth, survival, reproduction, and defense. These pathways not only convert simple molecules into the building blocks of life but also enable plants to adapt to environmental stresses. Synthetic pathways are fundamental to understanding plant biology, and they form the basis of applications ranging from agriculture to medicine (Amack.,et al 2020)..
Plant metabolism can be broadly divided into two categories: primary metabolism and secondary metabolism. Primary metabolic pathways are essential for plant growth and development, producing compounds such as carbohydrates, lipids, proteins, and nucleic acids. Secondary metabolic pathways, on the other hand, yield a vast array of specialized compounds, many of which are not directly involved in growth but play critical roles in defense mechanisms, signaling, and interactions with other organisms (Baltes.,et al 2015).
Synthetic pathways can further be grouped based on the type of compounds they produce, including carbohydrates, amino acids, fatty acids, terpenoids, phenolics, and alkaloids.The most well-known synthetic pathway in plants is the Calvin cycle, part of the broader process of photosynthesis. The Calvin cycle occurs in the chloroplasts and is responsible for fixing atmospheric carbon dioxide into organic molecules, specifically glucose. This sugar serves as the primary energy source for plants and as the building block for other essential macromolecules (Callaway.,et al 1997).
During the Calvin cycle, CO2 is fixed by the enzyme ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) and converted into 3-phosphoglycerate (3-PGA). Through a series of reactions, 3-PGA is transformed into glyceraldehyde-3-phosphate (G3P), which can then be used to synthesize glucose.Glucose is often stored as starch, a polysaccharide made up of long chains of glucose units. This starch is later broken down during periods of low photosynthesis, providing a steady energy supply to the plant (Chen.,et al 2020).
Proteins are vital to plant structure and function, serving roles in enzymatic activity, signaling, and structural support. The building blocks of proteins, amino acids, are synthesized through various pathways that depend on precursor molecules derived from the Calvin cycle and other metabolic routes.This pathway is crucial for synthesizing aromatic amino acids such as phenylalanine, tyrosine, and tryptophan. It begins with phosphoenolpyruvate (PEP) from glycolysis and erythrose 4-phosphate from the pentose phosphate pathway. These compounds are converted through a series of reactions into shikimic acid, a precursor to aromatic amino acids (Karimi.,et al 2015).
Aspartate and glutamate are two key amino acids that serve as precursors for the synthesis of other amino acids, such as lysine, methionine, and asparagine. These pathways are critical for nitrogen assimilation, as nitrogen is incorporated into amino acids to form proteins.Lipids, including fatty acids and triglycerides, play essential roles in membrane structure, energy storage, and signaling. Plants synthesize fatty acids primarily in the plastids through a pathway known as fatty acid biosynthesis (Letourneau.,et al 2011).
This pathway begins with the conversion of acetyl-CoA into malonyl-CoA by the enzyme acetyl-CoA carboxylase. Malonyl-CoA then undergoes a series of elongation reactions, resulting in the formation of long-chain fatty acids. These fatty acids are used to synthesize complex lipids such as phospholipids, which make up plant cell membranes, and triacylglycerols, which store energy in seeds and other tissues (Liu.,et al 2011).
Terpenoids, also known as isoprenoids, constitute the largest group of plant secondary metabolites. They are derived from five-carbon units called isopentenyl pyrophosphate (IPP), which are synthesized through two distinct pathways: the mevalonate pathway and the methylerythritol phosphate (MEP) pathway.Found primarily in the cytosol, the mevalonate pathway synthesizes IPP from acetyl-CoA. This pathway is involved in the production of sesquiterpenes and triterpenes, which play roles in plant defense and hormone regulation.Occurring in plastids, the MEP pathway produces IPP and its isomer dimethylallyl pyrophosphate (DMAPP). These compounds are precursors to monoterpenes, diterpenes, and carotenoids. Carotenoids, such as beta-carotene, are essential for photosynthesis and protect plants from oxidative damage (Liu.,et al 2016).
This pathway begins with the deamination of phenylalanine to produce cinnamic acid, which can be further modified to produce a wide variety of phenolic compounds, including flavonoids, lignins, and tannins.Lignin is a complex phenolic polymer that provides structural support to plant cell walls and aids in water transport. It is synthesized by polymerizing monolignols, which are derived from the phenylpropanoid pathway (Marzo.,et al 2006).
Alkaloids are nitrogen-containing secondary metabolites with potent biological activities. They are synthesized through various pathways depending on the precursor molecules, which are often derived from amino acids.Derived from ornithine, tropane alkaloids such as hyoscyamine and scopolamine are found in plants like belladonna and play roles in deterring herbivores. Tryptophan serves as a precursor for indole alkaloids, which include important pharmacological compounds such as vinblastine and reserpine (Vorholt,.,et al 2017).
Plant synthetic pathways represent a sophisticated network of biochemical reactions that allow plants to produce the wide array of compounds necessary for survival and interaction with their environment. From primary metabolites like carbohydrates and proteins to secondary metabolites such as terpenoids and alkaloids, these pathways enable plants to grow, defend themselves, and adapt to their surroundings. Understanding these pathways has broad implications for fields ranging from agriculture to pharmaceuticals, where plants serve as a source of essential nutrients, medicines, and bio-based materials.
Amack, S. C., & Antunes, M. S. (2020). CaMV35S promoter–A plant biology and biotechnology workhorse in the era of synthetic biology. Current Plant Biology, 24, 100179.
Indexed at, Google Scholar, Cross Ref
Baltes, N. J., & Voytas, D. F. (2015). Enabling plant synthetic biology through genome engineering. Trends in biotechnology, 33(2), 120-131.
Indexed at, Google Scholar, Cross Ref
Callaway, R. M., & Walker, L. R. (1997). Competition and facilitation: a synthetic approach to interactions in plant communities. Ecology, 78(7), 1958-1965.
Indexed at, Google Scholar, Cross Ref
Chen, C. C., Dai, L., Ma, L., & Guo, R. T. (2020). Enzymatic degradation of plant biomass and synthetic polymers. Nature Reviews Chemistry, 4(3), 114-126.
Indexed at, Google Scholar, Cross Ref
Karimi, A., Majlesi, M., & Rafieian-Kopaei, M. (2015). Herbal versus synthetic drugs; beliefs and facts. Journal of nephropharmacology, 4(1), 27.
Letourneau, D. K., Armbrecht, I., Rivera, B. S., Lerma, J. M, et al,. (2011). Does plant diversity benefit agroecosystems? A synthetic review. Ecological applications, 21(1), 9-21.
Indexed at, Google Scholar, Cross Ref
Liu, W., & Stewart Jr, C. N. (2016). Plant synthetic promoters and transcription factors. Current opinion in biotechnology, 37, 36-44..
Indexed at, Google Scholar, Cross Ref
Liu, W., & Stewart, C. N. (2015). Plant synthetic biology. Trends in Plant Science, 20(5), 309-317.
Marzo, V. D., & Petrocellis, L. D. (2006). Plant, synthetic, and endogenous cannabinoids in medicine. Annu. Rev. Med., 57(1), 553-574.
Indexed at, Google Scholar, Cross Ref
Vorholt, J. A., Vogel, C., Carlström, C. I., & Müller, D. B. (2017). Establishing causality: opportunities of synthetic communities for plant microbiome research. Cell host & microbe, 22(2), 142-155.