Over the last 50 years, the field of genetic engineering has developed rapidly due to the greater understanding of deoxyribonucleic acid (DNA) as the chemical double helix code from which genes are made. The term "genetic engineering" is used to describe the process by which the genetic makeup of an organism can be altered using "recombinant DNA technology." This involves the use of laboratory tools to insert, alter, or cut out pieces of DNA that contain one or more genes of interest.
In contrast, genetic engineering allows the direct transfer of one or just a few genes of interest between either closely or distantly related organisms to obtain the desired agronomic trait. Not all genetic engineering techniques involve inserting DNA from other organisms. Plants may also be modified by removing or switching off their own particular genes.
Limited to exchanges between the same or very closely related species
Little or no guarantee of any particular gene combination from the millions of crosses generated
Undesirable genes can be transferred along with desirable genes
Takes a long time to achieve desired results
Allows the direct transfer of one or just a few genes between either closely or distantly related organisms
Crop improvement can be achieved in a shorter time compared to conventional breeding
Allows plants to be modified by removing or switching off particular genes
Genes are molecules of DNA that code for distinct traits or characteristics. For instance, a particular gene sequence is responsible for the color of a flower or a plant's ability to fight a disease or thrive in an extreme environment.
Nature's Own Genetic Engineer
The "sharing" of DNA among living forms is well documented as a natural phenomenon. For thousands of years, genes have moved from one organism to another. For example, Agrobacterium tumefaciens, a soil bacterium known as "nature's own genetic engineer," has the natural ability to genetically engineer plants. It causes crown gall disease in a wide range of broad-leaved plants, such as apple, pear, peach, cherry, almond, raspberry, and roses.
The disease gains its name from the large tumor-like swellings (galls) that typically occur at the crown of the plant, just above soil level. Basically, the bacterium transfers part of its DNA to the plant, and this DNA integrates into the plant's genome, causing the production of tumors and associated changes in plant metabolism.
Application of Genetic Engineering in Crop Production
Genetic engineering techniques are used only when all other techniques have been exhausted (i.e., when the trait to be introduced is not present in the germplasm of the crop, the trait is very difficult to improve by conventional breeding methods, and it will take a very long time to introduce and/or improve such a trait in the crop by conventional breeding methods). Crops developed through genetic engineering are commonly known as transgenic crops or genetically modified (GM) crops. (See "GMOs: A Primer (of Sorts)," October 2016, for more information.)
Modern plant breeding is a multidisciplinary and coordinated process where a large number of tools and elements of conventional breeding techniques, bioinformatics, molecular genetics, molecular biology, and genetic engineering are utilized and integrated.
Development of Transgenic Crops
Although there are many diverse and complex techniques involved in genetic engineering, its basic principles are reasonably simple. There are five major steps in the development of a genetically engineered crop. But for every step, it is very important to know the biochemical and physiological mechanisms of action, regulation of gene expression, and safety of the gene and the gene product to be utilized. Even before a genetically engineered crop is made available for commercial use, it has to pass through rigorous safety and risk assessment procedures.
The first step is the extraction of DNA from the organism known to have the trait of interest. The second step is gene cloning, which will isolate the gene of interest from the entire extracted DNA, followed by mass production of the cloned gene in a host cell. Once it is cloned, the gene of interest is designed and packaged so that it can be controlled and properly expressed once inside the host plant. The modified gene will then be mass-produced in a host cell to make thousands of copies.
When the gene package is ready, it can then be introduced into the cells of the plant being modified through a process called transformation. The most common methods used to introduce the gene package into plant cells include biolistic transformation (using a gene gun) or Agrobacterium-mediated transformation. Once the inserted gene is stable, inherited, and expressed in subsequent generations, then the plant is considered a transgenic. Backcross breeding is the final step in the genetic engineering process, where the transgenic crop is crossed with a variety that possesses important agronomic traits and selected to obtain high-quality plants that express the inserted gene in a desired manner.
The length of time in developing a transgenic plant depends on the gene, crop species, available resources, and regulatory approval. It may take 6–15 years before a new transgenic hybrid is ready for commercial release.
Commercially Available Crops Improved through Genetic Engineering
Transgenic crops have been planted in different countries for 20 years, starting from 1996. About 191.7 million hectares were planted in 2018 with transgenic crops with high market value, such as herbicide-tolerant soybean, maize, cotton, and canola; insect-resistant maize, cotton, potato, and rice; and virus-resistant squash and papaya. With genetic engineering, more than one trait can be incorporated or stacked into a plant. Transgenic crops with combined traits are also available commercially. These include herbicide-tolerant and insect-resistant maize, soybean, and cotton.
New and Future Initiatives in Crop Genetic Engineering
To date, commercial GM crops have delivered benefits in crop production, but there are also a number of products in the pipeline that will make more direct contributions to food quality, environmental benefits, pharmaceutical production, and nonfood crops. Examples of these products include a triple-stack trait biotech rice with better yield amid abiotic stresses, biotech chestnut tree with resistance to chestnut blight, biotech citrus-greening-resistant citrus, potato enriched with beta carotene, biofortified sorghum, bacterial (Xanthomonas) wilt-resistant banana, bunchy top virus-resistant banana, and insect-resistant wheat, among others.
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