Bt Corn

For this STSE I will be discussing one of the most frequently produced genetically modified organism called Bt corn. To begin, this genetically modified plant organism is corn that has been transformed with the Bacillus thuringiensis bacteria gene(Fig. 5), allowing it to resist the European corn borer insect which is one of the most destructive insects to damage or reduce corn production and one of the most economically significant crop pests in the world(refer to Fig. 3 and 4). More specifically, this bacterium contains a gene that produces the Bt protein called Bt delta endotoxin which is toxic to the European corn borer(refer to Fig. 6). When European corn borers feed on Bt plants, they ingest the crystalline proteins which bind to the mid region of the insects’ gut, causing the cells in the area to burst from a water imbalance killing the corn borer. Therefore, through biotechnological techniques, the corn plant is given genetic traits that allow it to protect itself against the destructive European corn borer.

Process of Bt corn Production

Bt Corn

Bt corn Impacts on society, the environment and the economy

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Step 4: Gene design

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Step 5: Transformation

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Furthermore, the fourth step of this process involves designing the gene which ensures that the desired gene that produces Bt protein function’s effectively inside the different organism (corn plant). In this process, the gene undergoes several modifications for it to be effectively expressed when it is inserted into the corn plant. Therefore, the modification process involves changing the sequences in the regions of the gene that control gene expression.

1.First, a promoter sequence must be added to the gene in order for it to be correctly expressed (successfully translated into a protein product)(Fig. 14). The main of function of the promoter is to act as an on/off switch which controls and specifies the location and time the specific gene will be expressed. One of the main promoters currently used in transgenic crops is the CaMV35s which originates from a cauliflower mosaic virus gene(Fig. 15). When this specific promoter is used, the gene is expressed and the protein encoded by the gene will be produced throughout the life cycle of the cell in most tissues.

2.Also, there are instances where a cloned gene must be modified in order for it to achieve a greater expression in the cells of a plant. In Bt corn, the Bacillus thuringiensis gene is modified by replacing A-T nucleotides with G-C nucleotides without significantly changing the sequence of the gene. This results in a greater production of Bt protein encoded by the gene.

3.Furthermore, second region of a gene that usually undergoes modification in transgenes is the coding region which contains the coded information and specifies the amino acid sequence of a protein(Fig. 16). The amino acid sequence of a protein determines its shape and the function of a protein. In Bt protein, three coding regions for European corn borer resistance in Bt corn include Cry 1A (b), Cry 1A(c), and the Cry 9c(Fig. 17). In each region, crystalline proteins are encoded which cause insect larvae toxicity. When European corn borers feed on Bt corn plants, they ingest the crystalline proteins which bind to the mid region of the insects’ gut, causing the cells in the area to burst from a water imbalance killing the corn borer.

4.Finally, a termination sequence is added to the gene. The main function of the terminator sequence is to signal when the end of the gene sequence has been reached(Fig. 19).

5.Also, a selectable marker gene is added to the gene which identifies the plant cells or tissues that have successfully been inserted with the desired D.N.A gene. Also, this process is significant because the marker gene can also encode proteins that provide resistance to toxins such as herbicides and antibiotics(Fig. 18).

The Fifth step of this process is Transformation which is a change in a cell or organism that is caused by the introduction of new D.N.A. This process is accomplished through two main methods, the gene gun method and the Agrobacterium method.

1. The gene gun method, also known as micro- projectile bombardment method, is a process that begins with coating tungsten or gold particles (micro projectiles) with the plasmid DNA. Then, the coated particles are covered and placed on a macro-projectile which is then accelerated at a high velocity with air pressure and shot by a gun tool into the plant tissue on a petri dish. As the micro projectiles enter the cells, the transgenic products are released from the particle surface and incorporate into the chromosomal DNA of the cells(Fig. 20 and 21).

2. The Agrobacterium bacteria method is a process that involves the use of the bacteria known as Agrobacterium tumefaciens. This bacterium has the ability to infect plant cells with a piece of its DNA. The segment of DNA that is incorporated into the plants chromosomes is a tumor inducing plasmid. Scientists have genetically engineered this bacterium in order to remove the tumor inducing segment of the plasmid which prevents it from harming the corn plant that it is inserted. When the target plant is wounded, it sends off chemical signals which activate the plasmid. After the plasmid has been activated, it enters the plant cell through the wound. In this method, the specific process in which DNA is transferred from the cytoplasm into the nucleus or how it is incorporated into the plant chromosome is unknown(Fig. 22).

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Step 3: Gene Cloning

Step 6: Tissue culture and Backcross Breeding

Step 2: Amplification Amount of DNA through PCR

Step 1: DNA extraction

The final step in the production of Bt corn is tissue culture breeding and Backcross plant breeding.

In the breeding process, the final product plant tissues are grown under controlled environments in a series of mediums that contain nutrients and hormones. These plants undergo a series of tests to ensure that they contain the desired gene. Also, these tests monitor the activity of the gene, the inheritance of the gene, effects on the plant growth, yield and quality(Fig. 23). Then,in the process of Backcross breeding, the transgenic plants are crossed with breeding lines that have many genes for desired agronomic traits that result in high yields in a particular environment. This is done to combine the desired traits of elite parents and the transgene into a single line. The offspring are repeatedly crossed back to the elite line to obtain a high yielding transgenic line which results in plants that have a yield potential that is similar to current hybrids that expresses the trait encoded by the new transgene(Fig. 24).

The second step of this genetic engineering process is to use PCR (polymerase chain reaction) to amplify many copies of the specific segment of the extracted DNA in order to produce enough DNA to be effectively tested and inserted into the desired organism.

1. To begin, in PCR, The DNA sample to be amplified is separated by being heated to temperature of 95⁰C. This causes the double stranded DNA to denature into single strands.

2.The DNA sample is cooled to a temperature between 50⁰C-72⁰C in the presence of two nucleotide primers. This allows the DNA primers to anneal, or base pair, with the 3’ ends of the single stranded DNA (old strand) to be amplified in the 5’—3’ direction.

3.The DNA sample is then heated to a temperature of 72⁰C, which is the optimal temperature for Taq polymerase. The enzyme then synthesizes DNA by the addition of free nucleotides to the ends (3’) of the primers via complementary base pairing in the 5’—3’ direction.

4. PCR is repeated several times. Each cycle doubles the amount of copies of DNA target sequence.

(Fig. 12 and Video 1)

The first step in the genetic engineering process is DNA extraction from another organism which is accomplished by scientists taking a sample of Bacillus thuringiensis, the bacteria that contains the gene of interest. In this initial process DNA is isolated from the other parts of the cell and the main Biotechnology tools are Restriction Endonucleases and DNA Ligase. To begin, the Restriction Endonucleases are enzymes that are able to cleave double stranded DNA into fragments at specific sequences of nucleotide bases(Fig 9). Each restriction enzyme is specific to a certain sequence of nucleotide bases. Therefore, the restriction enzymes scan the DNA from the sample of Bt bacteria until they find the specific sequence of nucleotide bases for the desired gene that they recognize. Once the specific sequence is found, the restriction enzymes bind to the recognition site and begin to cleave the DNA, disrupting Hydrogen bonds between strands and the phosphodiester bonds between adjacent nucleotides. Then, “the glue”, DNA ligase enzyme is used to join together the blunt or sticky ends of the cleaved DNA fragments(Fig. 10 and 11). Hydrogen bonds form easily between complimentary Sticky ends of DNA; however, ligase is needed to form the phospodiester bonds in the backbone.

Shortly after the second step, the third step in Bt corn production commences. In this step, scientists use gene cloning to manipulate the DNA to separate and produce many identical copies of the specific gene for the BT protein. This is recombinant DNA technology that ultimately allows scientists to use a gene to produce the specific proteins.

1.First, restriction enzymes that purified and fragmented the isolated DNA in the earlier stages of this process made sticky ends. (Fig, 13 and Video 2)

2.The DNA fragments are then incorporated into plasmids which have been cleaved with the same restriction enzyme that cleaved the DNA fragments. (Fig, 13 and Video 2)

3.DNA Ligase then joins the sticky ends of the plasmid and DNA with phosphodiester bonds. (Fig, 13 and Video 2)

4.Next, the plasmids are incorporated into the bacteria host cells by transformation. (Fig, 13 and Video 2)

5.Finally, the cells are plated out (put into petri dishes) and the cell with the desired gene is located and isolated. (Fig, 13 and Video 2)

In this process, an antibiotic resistant gene is also inserted along with the cleaved DNA fragments into the plasmid which is then also inserted into the bacteria host cell. This allows the carrier cell to be amplified successfully through the process of transformation. Transformation will amplify the carrier cells but at the same time it will only amplify the carrier cells with the desired DNA. This process involves the carrier cell being placed into two mediums, one that contains a specific antibiotic and one that does not contain the antibiotic. After the carrier cells are placed into both mediums, the medium that does not contain the antibiotic grows substantially while the other medium that does contain the antibiotic grows slightly. This is because the carrier cells that contain the desired DNA and antibiotic-resistance gene will not grow on the medium with the antibiotic on it. This ensures that the desired DNA is going to be contained within all of the host cells and as the host cells grow, the DNA inside the cell will also grow with it. Therefore, the DNA will be successfully amplified or cloned to an appropriate amount. (Fig. 13)

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Introduction

Impacts on Society

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Environmental Impacts

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3. The thorough investigation of the Bt corn product has led scientists to believe that it is as safe as non-Bt corn for human and animal health(Fig. 34 and 35). After two years of scientific research, in October, 2001, the EPA released a review giving the final conclusion that Bt corn “poses no risks to human health or the environment”(Fig. 33).

5. Also, the process of genetically modifying the corn and transforming it with the Bt bacteria gene can allow scientists to also use genetic engineering to increase the amounts of vitamins and other nutrients contained by the plant(Fig 38). This is very significant for developing countries and regions around the world where people suffer from nutritional deficiency(Fig. 39).

1. To begin, Bt corn is a genetically engineered plant product that is very beneficial to the consumers since the grain from this product is often of better quality than grain from conventional corn hybrids(Fig. 29). Corn crops that have not been genetically modified and transformed with the Bacillus thuringiensis bacteria gene are defenseless against insects such as the European corn borer and as a result, the damage that these insects cause reduce the grain quality of the conventional corn plants that have not been genetically modified(Fig, 30).

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3. Another environmental benefit of Bt corn is that it does not have any damaging impacts on non-target organisms such as bees, ladybugs, butterflies, beetles, birds and small mammals. This is because the mechanism that is used by the Bt protein to control the European corn borer and other damaging insects is highly specific(Fig 49, Fig. 50, Fig.51, Fig52, Fig.53). Therefore, most of the non-target organisms in the area (field) in which Bt corn crops are grown digest the protein along with all the other nutrients in their normal diet.

1. The Bt corn product has significant impact on the environment and agriculture since there is evidence that Bt corn plants provides a form of protection to non-Bt corn plants and other plants such as potato and pepper crops that have not been genetically engineered and transformed using Bt bacteria gene by reducing the overall population of corn borers and other destructive insects(Fig. 46). In some areas, a moth can go through three generations in one summer and by controlling the first generation larvae with Bt corn, fewer moths will emerge to the start the second and third generations.

4. The most important characteristic of Bt corn is that is contains a gene that produces a toxic protein that resists damaging insect predators such as the corn borer. Therefore, this product reduces the need for using general insecticides(Fig. 54) that may damage other species of insects that do not pose any threat to the Bt corn plant.

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2. Finally, optimal corn crops are produced through the process of genetically engineering corn which is significant because it can allow farmers to produce more corn plant products at a cheaper rate which will cause the prices for corn in grocery stores and markets to reduce(Fig. 44). The faster production rate of corn through the process of genetic modification can also allow the corn plant to grow and thrive in environments it would usually be unable to effectively grow in(Fig. 45).

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1. To begin, studies show that the production of genetically modified corn (Bt corn) has led to significant economic return as a result of large amounts of crop yields being protected in the years when there is a heavy outbreak of European corn borer(Fig. 42 and 43)which are insects that cause great damage to the corn crops. From 1996-2001, the increased yields of crop as a result of the use of Bt corn plants allowed farms to receive a return of $567 million, for a net loss of $92 million

5. Although the Bt corn plant may have harmful effects on some organisms that ingest the Bt protein, the only alternative to this genetically modified plant product is the use of non-Bt corn plants which need to be protected using conventional insecticides. Therefore, Bt-corn is the best alternative because the insecticides used to maintain non-Bt corn have more harmful impacts on non-target insects(Fig. 54).

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6. A negative social and environmental of Bt corn is that strictly controlling the genetic components and production of the corn can reduce crop diversity which may lead to many problems such as the outbreak of a disease(Fig. 40 and 41).

4. Another social benefit of Bt corn is its consumption does not lead to any possible allergic reactions because studies show that Bt protein is not normally found in the corn. Also, studies show that most food allergies are extremely resistant to reactions of neutralization through heat, acid and the digestive enzymes such as proteases. The allergenic products are usually present in high concentrations and are glycosylated. However, unlike these allergenic products, the Bt protein is quickly degraded in vitro by digestive fluids(Fig. 36 and 37).

2. Furthermore, the collaboration of many countries around the world has led to the development of very strict food safety assessment procedures which involve thorough study and research of scientific data performed by independent government experts prior to product approval(Fig.31). Scientific study has allowed scientists to determine that the plant biology and characteristics of Bt corn is substantially equivalent to non-Bt corn. Therefore, this genetically modified product is beneficial and useful as it provides sufficient nutrition and is similar in wholesomeness to non-Bt corn(Fig.32).

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2. Also, the use of Bt corn plants to reduce the corn borer population is extremely beneficial because the larvae bore tunnels in the ears of the corn plants which provides an entry point for other pathogens(Fig. 47). The most particular pathogen invasions caused by corn borer damage are fungi infections which ultimately affect the quality of the grain and reduce yields. A specific fungal infection known as Fusarium, or “ear rot”, produces molds that are very unhealthy for animals eating the infested corn plant grain(Fig. 48). Bt protected corn plants have lower level of toxins produced by molds including fumonisin and deoxynivalenol . Contamination with molds produced by fungal infections are extremely harmful since fumonisins can cause fatal leukoencephalomalacia in horses, pulmonary edema in swine, and cancer in laboratory rats. Therefore, corn that is genetically engineered and transformed with the Bt bacteria gene is significant because the Bt gene makes an essential contribution to grain quality and safety. Also, the reduced levels of toxins in corn plants allow USA farmers to save a total of $23 million annually.

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6. Finally, a the negative impact that Bt corn has on the environment is that it will cause the control of corn borers and other destructive insects to become more difficult since a progressively increasing population of these insects will become resistant to the Bt protein through natural selection(Fig. 55).

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