Genetic modification, a genetic engineering process, is simply manipulating the gene to alter the genetic makeup of the organisms to select desired characteristics or traits (Pyne et al., 2011). This technology has improved the quality of human life and the environment over the years by creating transgenic plants and other organisms. With gene manipulation, it has become possible to revolutionize plant biomass yield and conversion efficiency to biofuel production.
The increasing demand for sustainable green energy and the negative consequences, such as global warming and energy insecurity of fossil fuels, have triggered plant biomass's sustainable supply and production. But, genetic modification technology has made a significant impact in the global green energy transition by altering the characteristics and properties of lignocellulosic (plant dry matter) biomass, oil, sugar, and starch crops and transform them into desired bioenergy or biofuel resources.
Biofuels are generally produced from the biomass of first- and second-generation energy crops. The first-generation biofuel includes the most common conventional energy, bioethanol, and biodiesel deriving from sugar (sugar cane and sugar beet), starch (corn, wheat, and potato), and oil (sunflower, soybean, and rapeseed). The feedstocks are associated with natural food versus fuel competition.
Hence to overcome this issue, the lignocellulosic biomass is utilized to produce second-generation biofuel (Davidson, 2008). Most of this biomass consists of woody, non-edible parts of plants. The agricultural residues of rice and wheat straw, corn stover, grass plant residue, and bagasse are the most common source of lignocellulosic biomass. This resource is already the by-product and, therefore, reduces the competition between the land for fuel and food production.
Composition of lignocellulosic biomass
Lignocellulosic biomass mainly consists of three main components: cellulose, hemicellulose, and lignin, as well as pectin as minor components. Cellulose is a crucial polysaccharide that signals cells to grow and connects cells to form tissues. Hemicellulose contributes to strengthening the cell wall by interaction with cellulose. Lignin acts as a natural defence against pathogens and provides structure to the plant. Cellulose, which is insoluble in water, is the main component in lignocellulosic biomass.
Genetic modification of plant biomass
In lignocellulosic biomass, the cellulose gets bonded with hemicellulose and lignin. The fermentation process for hemicellulose becomes more complicated than cellulose. As a result, biofuel production from lignocellulosic and other plant biomass by the conventional approach is expensive, not feasible for commercial scale, and requires advanced technology.
Therefore, third-generation biofuel crops, including microalgae and seaweed, are utilized as alternative biomass. The third-generation biofuel crop isn’t relevant to discuss in this article. Further, to ease the process and reduce the cost of biofuel production, gene modification comes into play. This modification process is known as fourth-generation biofuel that involves genetically modified biomass.
In fourth-generation biofuel production, the plant biomass is modified genetically to take high carbon contents or other essential products to produce sustainable biofuels. After gene manipulation, cellulase and hemicellulase hydrolysis is possible to degrade cellulose and hemicellulose. This conversion route is called enzymatic hydrolysis. Otherwise, the biomass is treated with a complicated thermochemical process at high temperatures and pressure to disintegrate the long-chain and complex carbon molecules.
After the disintegration, the genetically modified enzymes can improve the conversion efficiency of the downstream process. Finally, the fermentation process followed by the distillation process converts monomeric sugars into pure biofuel (Davidson, 2008; Fatima et al., 2018).
Applications of genetically modified plant biomass
The concept of genetic engineering has enormous potential in stable and high yield biomass production and conversion efficiency of biomass. Genetic engineering technology can modify lignin to reduce biomass pre-treatment processes and conversion costs. Also, this process can manipulate crops to develop varieties with increased polysaccharides (C6 chains) and fewer lignin levels.
Gene manipulation can play a significant role in harnessing improved crop yields and overcoming abiotic stress to balance the food and fuel competition. The genetic modification of crops, such as tobacco, alfalfa, corn, and rice, enhances biomass quality and yields, and the future seems promising (Sticklen, 2008; Chen and Dixon, 2007).
Moreover, a plant with nitrogen-fixing capacity that consumes less water with high biomass yields and conversion efficiency to biofuels is possible with genetic modification (Furtado et al., 2014). Similarly, the non-seed plant produces oil in leaves, stems, and other non-seed parts of plant biomass after gene manipulation. Also, the main ingredients used in biodiesel, such as bio-based lubricants and esterified fatty acids, can be bioengineered from oilseed crops such as Jatropha (Akashi and Nanasato, 2018).
C4 grass (4 carbon sugar, warm-season grass), such as Napier grass (Pennisetum purpureum), sorghum (Michanthusgiganteus), and switchgrass (Panicum virgatum) and the C3 (3 carbon sugar, cool-season grass) plant species like poplar, aspen, and willow are considered the best source of biomass for biofuel production. Gene manipulation of the C4 and C3 grass boost the yield of biomass. The genomic investigation in biomass is widespread in the United States, Europe, and Brazil (Brandon and Scheller, 2020).
Biswal et al. (2015) reported that the significant improvements in the biomass with the suppression and elimination of various genes aids in the synthesis of specific polysaccharides. Different kinds of polysaccharide biosynthesis involve cellulose, hemicellulose, and pectin modification.
Similarly, the ideal bioenergy crop content results from increased cellulose biosynthesis as it contains a C6 sugar molecule. Also, the co-overexpression of specific genes codes for a rise in enzyme galactose content by 80% in Arabidopsis (Brandon and Scheller, 2020). The pectin modification by overexpression of the pectate lyase gene resulted in improved saccharification (Biswal et al., 2015).
In a nutshell, the concept of plant genetic modification has a remarkable possibility of meeting the world's biofuel demand. It acts as an alternative way to mitigate the carbon footprint and proceeds in a sustainable way to abridge the dependency on fossil fuels. Genetic modification of plant biomass allows the significant change in genes to produce the desired quality and volume quickly. Numerous studies are going on, and researchers continue to look for solutions to the global energy crisis as plant gene recombination acts as a viable alternative.
The manipulation of plant genes enhance the plant biomass to biofuel or bioenergy conversion process and optimize the resources available to meet the affordable energy demand in an environment-friendly manner. With regulatory frameworks designed and participation of private and public sectors in putting plant gene modification as a plan for biofuel, the environment can prolong and adds value to the global energy mix.