Genetically Modified Organisms and Crops

Genetically modified crops (GM crops) are crops which have had their DNA altered in a way that does not occur naturally. Individual genes which promote durability or nutritional value are transferred from one organism to another to create biologically robust plants. Initially, it was developed in response to growing concern about protecting crops from insects, unusual weather patterns and harmful pesticides. GM crops are becoming more and more mainstream, dividing public opinion about the health and environmental impacts of producing and consuming crops produced in a lab.
To produce a GM plant, new DNA is transferred into plant cells. Usually, the cells are then grown in tissue culture where they develop into plants. The seeds produced by these plants will inherit the new DNA. It actually involves adding a specific stretch of DNA into the plant’s genome, giving it new or different characteristics. This could include changing the way the plant grows, or making it resistant to a particular disease. The new DNA becomes part of the GM plant’s genome which the seeds produced by these plants will contain.

Early farmers discovered that some crop plants could be artificially mated or cross-pollinated to increase yields. Desirable characteristics from different parent plants could also be combined in the offspring. When the science of plant breeding was further developed in the 20th century, plant breeders understood better how to select superior plants and breed them to create new and improved varieties of different crops. This has dramatically increased the productivity and quality of the plants we grow for food, feed and fiber.
Plant breeding can be considered a co-evolutionary process between humans and edible plants. Earlier, farmers selected the best looking plants and seeds and saved them to plant for the next season. Then, once the science of genetics became better understood, plant breeders used what they knew about the genes of a plant to select for specific desirable traits to develop improved varieties. Both conventional plant breeding and GM deliver genetic crop improvement. Genetic improvement has been a central pillar of improved agricultural productivity for thousands of years. This is because wild plants make very poor crops. Natural selection can only favour plants that can compete with neighbouring plants.
The end result of conventional plant breeding is either an open-pollinated (OP) variety or an F1 (first filial generation) hybrid variety. OP varieties, when maintained and produced properly, retain the same characteristics when multiplied.
While an extremely important tool, conventional plant breeding also has its limitations. First, breeding can only be done between two plants that can sexually mate with each other. This limits the new traits that can be added to those that already exist in a particular species. Second, when plants are crossed, many traits are transferred along with the traits of interest - including those traits that have undesirable effects on yield potential.
There are two main reasons why GM might be preferable. Firstly, the gene of interest might not exist in a species that can be successfully crossed with the crop. The gene might come from an entirely different kingdom, such as a bacterium, or it might come from a different plant species. Secondly, today’s high yield crop lines have carefully honed combinations of genes. If a useful gene or gene variant is discovered in a wild relative, crossing the high yield line with the wild relative will result in mixing together the genomes of the two parents, destroying the carefully selected combination of genes in the high yield line. Using modern molecular breeding techniques, it is possible to reassemble those gene combinations over relatively small number generations.

Agricultural plants are one of the most frequently cited examples of genetically modified organisms (GMOs). Some benefits of genetic engineering in agriculture are increased crop yields, reduced costs for food or drug production, reduced need for pesticides, enhanced nutrient composition and food quality, resistance to pests and disease, greater food security, and medical benefits to the world's growing population. Advances have also been made in developing crops that mature faster and tolerate aluminum, boron, salt, drought, frost, and other environmental stressors, allowing plants to grow in conditions where they might not otherwise flourish. Other applications include the production of bioplastics or ornamental plant products.
Genetically Modified Soya Bean.A genetically modified soybean is a soybean (Glycine max) that has had DNA introduced into it using genetic engineering techniques. In 1996 the first genetically modified soybean was introduced to the U.S. market, by Monsanto.
Roundup Ready soybeans are a series of genetically engineered varieties of glyphosate-resistant soybeans produced by Monsanto. Glyphosate kills plants by interfering with the synthesis of the essential amino acids phenylalanine, tyrosine and tryptophan. These amino acids are called "essential" because animals cannot make them; only plants and micro-organisms can make them and animals obtain them by eating plants. Plants and microorganisms make these amino acids with an enzyme that only plants and lower organisms have, called 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). EPSPS is not present in animals, which instead obtain aromatic amino acids from their diet. Roundup Ready Soybeans express a version of EPSPS from the CP4 strain of the bacteria Agrobacterium tumefaciens, expression of which is regulated by an enhanced 35S promoter (E35S) from cauliflower mosaic virus (CaMV), a chloroplast transit peptide (CTP4) coding sequence from Petunia hybrida, and a nopaline synthase (nos 3') transcriptional termination element from Agrobacterium tumefaciens. The plasmid with EPSPS and the other genetic elements mentioned above was inserted into soybean germplasm with a gene gun.
Genetically Modified Papaya.The Rainbow papaya is an F-1 hybrid variety of papaya produced by crossing Hawaii's yellow-flesh Kapoho Solo variety with the red-flesh SunUp. Researchers had done research since 1984 to develop this Rainbow variety, which includes a gene that made the papaya plants resistant to the ringspot virus—similar to the way a vaccine makes people immune to disease.
Papaya ringspot virus is a killer. Once a plant is infected, it can never recover. Aphids feeding on the leaves of infected papaya trees effectively transmit the virus within seconds of probing on healthy trees. Young seedlings die quickly and never grow to produce fruit. Older trees develop yellowed leaves. They produce smaller and smaller fruit and are doomed to a slow death. Generally crops with resistance to viral disease may be developed through genes derived from viral sequences providing pathogen derived resistance (PDR), genes from various other sources that can interfere with target virus, and natural resistance genes. The concept of pathogen derived resistance (PDR) is a new approach for PRSV management. Pathogen derived genes interfere with the replication process of viruses in their host plants in different ways. So far, PRSV-resistant transgenic papaya has been developed through coat protein (CP), RNA silencing, and replicase gene technology.
Pros of GMs

  1. GMs advance the quality of grown food
  2. GMs are easier to cultivate and boost yields on existing lands
  3. Chemicals usage on GM crops is lesser compared to other crops.
  4. According to the FDA, GMO foodstuffs potentially meet equal requisites as other foodstuffs.
  5. GMOs are able to preserve energy, soil and water
  6. It protects crops from extinction

Cons of GMOs

  1. They might contribute to a rise in allergic reactions.
  2. GMs may contribute to antibiotic resistance and herbicide resistance occurs even without genetic modification.
  3. GMO crops can contaminate other fields.


RNA interference-mediated suppression mechanism gives us a genetically modified tomato namely Flavr Savr Tomato.Scientist introduced a suppression of the polygalacturonase (PG) gene on tomato, resulting from transformation of an antisense expression cassette of the PG cDNA (pCGN1436).
The FLAVR SAVR tomato was created by Agrobacterium-mediated transformation in which the transfer-DNA (T-DNA) contained a copy of the tomato PG encoding gene in the antisense orientation. In addition, the T-DNA contained sequences encoding the enzyme neomycin phosphotransferase II (NPTII). The expression of NPTII activity was used as a selectable trait to screen transformed plants for the presence of the antisense-PG gene. Transcription of the antisense-PG gene did not result in the expression of any novel protein. There was no incorporation of translatable plasmid DNA sequences outside of the T-DNA region.

Diagram of the sequenced 13,621-bp T-DNA insertion and flanking genomic regions.The mechanism of decreased PG activity in FLAVR SAVR tomato is likely linked to the hybridization of antisense and sense mRNA transcripts, resulting in a decreased amount of free positive sense mRNA available for protein translation. The measured level of PG activity in transgenic FLAVR SAVR tomato was found to be less than 1% of PG activity found in the unmodified parental line. The presence of NPTII protein has been judged to be insignificant with respect to any human health risk due to exposure. Alpha-tomatine is the principal naturally occurring glycoalkaloid in tomato, and the level of a-tomatine decreases as the fruit matures so that the amounts in vine-ripened red tomatoes are negligible. Solanine and chaconine, which are the main glycoalkaloids occurring in potato, have been found in tomato in lesser amounts.

Discuss the advantages of the outcome


Tomatoes have a short shelf-life in which they remain firm and ripe. This lifetime may be shorter than the time needed for them to reach market when shipped to markets and the softening process can also lead to more of the fruit being damaged during transit. So through genetic engineering, scientists have found a way of lengthening rotting period and therefore increasing the shelf life.
Other than reduced polygalacturonase activity, the disease, pest and other agronomic characteristics of the FLAVR SAVR tomato were comparable to unmodified varieties. The transgenic tomato is expected to replace other tomato cultivars currently in use due to improved quality and handling characteristics. Hence, it will provide an alternate or additional choice to consumers and food manufacturers.

Identify the enzyme involved in the transgenic strategy depicted\n5-enolpyruvylshikimate-3-phosphate (EPSP) synthase is an enzyme produced by plants and microorganisms. EPSP synthase is an attractive target for the development of new antimicrobial agents effective against bacterial, parasitical, and fungal pathogens. A valuable lead compound in the search for new drugs and herbicides is glyphosate, which has proven as potent and specific inhibitor of EPSP synthase.

EPSPS catalyzes the chemical reaction:

Glycines (glyphosate) are herbicides that inhibit 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase, a key enzyme in the shikimic acid pathway, which is involved in the synthesis of the aromatic amino acids. EPSP inhibition leads to depletion of the aromatic amino acids tryptophan, tyrosine, and phenylalanine that are needed for protein synthesis. Eventually this result in organism death from lack of aromatic amino acids the organism requires to survive.
Glyphosate is successfully used as a herbicide, being the active ingredient of the widely used weed control agent Roundup, and was recently shown to inhibit the growth of the pathogenic parasites Plasmodium falciparum (malaria), Toxoplasma gondii, and Cryptosporidium parvum .
EPSP synthase catalyzes the transfer of the enolpyruvyl moiety from phosphoenol pyruvate (PEP) to shikimate-3-phosphate (S3P) forming the products EPSP and inorganic phosphate. The reaction is chemically unusual because it proceeds via C–O bond cleavage of PEP rather than via P–O bond cleavage as in most PEP-utilizing enzymes. Glyphosate inhibits EPSP synthase in a slowly reversible reaction, which is competitive versus PEP and uncompetitive versus S3P.

References:

 

  • https://www.nature.com/scitable/topicpage/genetically-modified-organisms-gmos-transgenic-crops-and-732/
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC29264/
  • https://www.canada.ca/en/health-canada/services/food-nutrition/genetically-modified-foods-other-novel-foods/approved-products/suppressed-polygalacturonase-activity-flavr-savr-tomato.htmlwww.wikipedia.comwww.pnas.org