Dr Sarita Jaiswal is an accomplished Plant Scientist with +15 years of R&D experience with specialization in cereal & pulse crop biochemistry and genomics. She is Research Specialist at University of Saskatchewan, Saskatoon, Canada and served in different capacities for 10 years. She also works as a Regulatory Specialist. She is a two times young scientist (Indian Society of Plant Physiology & KK Nanda Foundation for Advancement of Plant Sciences) award winner. She is an Honorary Advisor to various reputed firms and reviewer of multiple Journals of International repute.
The very existence of human life on earth depends on the plants. One of the fundamental biochemical reactions, which makes plants autotrophic, is photosynthesis. It transforms celestial energy to chemical equivalents. The autotrophic plants not only transform this energy for their functioning but also store the excess in compact form, which we know as “starch”. We all are familiar with the principle of conservation of energy, “Energy can neither be created nor be destroyed, it can only be transformed.” In a plant’s chloroplast cells this transformation is completed with the generation of ATP, the ultimate currency for the existence of living organisms. In plants, the capture and storage of solar energy involves two separate reactions, termed the light and dark cycle of photosynthesis. The two mechanisms, which lead to the existence of life on earth, intrigued researchers for centuries.
In the light cycle solar energy powers chlorophyll electrons to move along a chain of different acceptors in the thylakoid membrane (also referred as electron-transport chain). The chlorophyll obtains its electrons from water (H2O), producing O2 as a by-product. To synthesize oxygen-generating organelle is definitely a charm for creation in synthetic plant biology. Julian Melchiorri, a graduate student in innovation design engineering at the UK’s Royal College of Art (2014), created the synthetic leaf, which produces oxygen, by absorbing light, water and carbon dioxide. This artificial leaf incorporates chloroplasts extracted from actual plant cells suspended in a material made from silk protein.
This artificial leaf is still far from the competing all leaf functions in photosynthesis and performs only a part of the light cycle. During the electron-transport process, H+ is pumped across the thylakoid membrane, and the resulting electrochemical proton gradient drives the synthesis of ATP in the stroma. In the dark cycle, the ATP and the NADPH produced during the light cycle serve as the source of energy and reducing power for generation of carbohydrate and ultimately fixing atmospheric CO2. The carbon-fixation step begins in the chloroplast stroma and continues in the cytosol. It produces sucrose and many other organic molecules inside the plant’s leaf, which later get transferred to other parts.
To create a system like chloroplast /mitochondria is the ultimate fancy in the area of synthetic biology. Artificial chloroplasts can power nonliving mini-reactors to produce molecules that living cells cannot. These mini synthetic reactors will be more efficient as their main objective is only processing with no energy partitioning to grow, reproduce or maintain other life-like functions. The entire system will focus on production of target molecules. Artificial photosynthesis can drive tiny, non-living, solar-powered factories that churn out therapeutic drugs. These artificial systems can even provide a solution for sequestering atmospheric CO2.
There are six naturally occurring carbon fixation pathways in plants, which convert CO2 to sugar. The carboxylase involved in bio-catalysis is key to its sustainability. In 2016, Tobias Erb and his group at the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany, designed a seventh pathway for fixing CO2, the crotonyl-coenzyme A (CoA)/ethylmalonyl-CoA/hydroxybutyryl-CoA (CETCH) cycle. This artificially designed pathway is 20% more efficient than natural classic CO2 fixation cycles. Tobias with his colleague Tarryn Miller created an artificial chloroplast. They included spinach chloroplast membranes in the artificial system to carry out photosynthetic electron transport. CETCH cycle enzymes use that energy to break down CO2 and convert it into glycolate. Glycolate can further be used for generating organic products.
The next advancing step in creating synthetic plants like biology is to generate starch from fixed CO2.
In autotrophic plants, the excess energy (glucose/sucrose) transforms into compact starch granules and acts as storage deposit for later use. Evolution of human civilization very much relied on this converted energy format. The next advancing step in creating synthetic plants like biology is to generate starch from fixed CO2. Starch is the backbone of the energy cycling of the planet earth. Plants convert celestial energy in the process of photosynthesis and store it as starch in albino plastids termed as amyloplasts. Starch as an osmotically inert chemical form, stores carbon in highly dense nature (~1.6g cm-3). It is mainly composed of amylose and amylopectin. Amylose is essentially linear with few inter-dispersed branches while amylopectin is a highly branched glucan structure. Granule bound starch synthases (GBSS) is mainly involved in the enzymatic machinery of amylose synthesis. In contrast to this amylopectin synthesis if mediated by an array of biosynthetic enzymes including starch synthases (SSII, SSIII, SSIV), starch branching (SBEI, SBEII) and debranching enzymes (isoamylases and pullulanases).
An artificial cell-free chemoenzymatic starch synthesis from carbon dioxide can be a new route with the possibility to shift starch production from traditional agricultural cultivation to industrial manufacturing. Cai Tao from Tianjin Institute of Industrial Biology (TIB) (2021) created the artificial starch anabolic pathway by assembling 11 core reactions. Based on “building block” strategy model, researchers integrated chemical and biological catalytic modules to utilize high-density energy and high-concentration CO2 in a biotechnologically innovative way. They further optimized this hybrid system using spatial and temporal segregation by addressing issues such as substrate competition, product inhibition, and thermodynamic adaptation. The artificial route can produce starch from CO2 with an efficiency 8.5-fold higher than starch biosynthesis in maize, suggesting a big step towards going beyond nature. It provides a new scientific basis for creating biological systems with unprecedented functions.
The Anglo-Japanese research team in 2019 with Professor Erwin Reisner as the leading scientist of the Cambridge university created an artificial leaf prototype. The prototype used little solar cells to absorb the light, water and carbon dioxide and generated syngas – specifically carbon monoxide and hydrogen. They further improvised it in the form of a leaf using cobalt photocatalyst. Instead of syngas this artificial leaf generates formic acid.
In India, a research group led by Chinnakonda S Gopinath, a senior scientist at the Council of Scientific and Industrial Research’s National Chemical Laboratory in Pune (2017) developed a leaf-like device capable of generating hydrogen fuel from water.
In India, a research group led by Chinnakonda S Gopinath, a senior scientist at the Council of Scientific and Industrial Research’s National Chemical Laboratory in Pune (2017) developed a leaf-like device capable of generating hydrogen fuel from water. This device contains semiconductors stacked in a manner to simulate the natural leaf system. When light strikes the semiconductors, electrons move in one direction, producing electric current which further breaks down water to generate hydrogen. This palm size model can generate six litres of hydrogen fuel in an hour.
These small steps in human’s evolution to achieve equilibrium with optimal utilization of photonic energy, will drastically transform every aspect of life, however, setting its timeline is not plausible yet.
These small steps in human’s evolution to achieve equilibrium with optimal utilization of photonic energy, will drastically transform every aspect of life, however, setting its timeline is not plausible yet. It is our next step towards resolving the energy crisis, resolving climatic change, food crisis and eventually, boosting human’s expansion to utilize untapped resources of the universe.
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