Intoduction to GM Foods and Trangenic Plants
Genetically modified (GM) organisms or genetically engineered (GE) organisms are basically plants, animals, or any organism whose DNA is being altered by using various genetic engineering techniques. On the other hand, Transgenic plants are plants having genes inserted into them derived from another species; the inserted genes can have origin from species within the same kingdom (plant to plant) or among different kingdoms (bacteria to plant). In many cases, the inserted DNA has to be modified slightly in order to be correctly and efficiently expressed in the host organism. Here, transgenic techniques have been utilized to furnish better agricultural products by making transgenic plants.
Genetically modified (GM) foods are transgenic plants that are used as a food, developed and marketing since there is some perceived advantage either to the producer or consumer of these foods. The GM crops currently in the market are primarily intended at an improved level of crop protection through the introduction of resistance against insects, plant pathogen, and increased resistance towards herbicide and other climatic states of affairs like salt and drought resistance. In some of the GM crops higher nutritional quality and yield have also been introduced. Numerous techniques are employed at the molecular level to integrate or create new resistance factors in a plant which can be summarized as follows:
1. Insect Resistance
Insect-pests are the major scourge of agriculture down the ages as important crops and their high-yielding genotypes are highly susceptible to insect pests. The introduction of chemical pesticides has brought about a significant change in pest management practices but. unfortunately, resulted in adverse effects on human health, other biological organisms, and the environment. Although complete elimination of pesticides is neither feasible nor advisable; it is imperative to reduce the consumption of pesticides in agriculture and the environment for practicing safe and sustainable farming. Effective alternatives are now available in the form of genetically engineered crops resistant to insect pests that can be integrated into agricultural ecosystems. Insect-resistant transgenes whether of plant, bacteria, or any other origin can be introduced into plants to augment the level of resistance. These genes are obtained from micro-organisms like the Bt gene from Bacillus thuringiensis, ipf (isopentyl transferase) gene from Agrobacterium tumefaciens, and Pht gene from Phtorabdus luminescence, which when introduced into some specific crop provide resistance against the specific insects.
A typical example of this is Bt Cotton, which has been developed by the insertion of the Bt gene. Bt gene codes for the Cry-proteins which are toxic mostly against Lepidopteron larvae but some are specific for Dipteran and Coleopteran insects. The toxins are converted into an active form upon infestation by susceptible insects, thereby killing these insects when they visit the cotton plant.
Monsanto introduced its first-generation Bt cotton, called Bollgard I (BG-I) in 2002 and Bollgard II (BG-II) in 2006, the latter of which is still the de facto GM cotton variety providing immunity to the plants from pests like American and pink bollworms in India. There has been an observable reduction in insecticide use, suppression of pests, and increased farmer profits with the employment of the Bt cotton. That is why it is presently cultivated in 10.8 million hectares of land area in India with nine states which include Maharashtra, Gujarat, Punjab, AP, Tamilnadu, MP, Haryana, and Karnataka on a larger scale and West Bengal, UP, Assam, and Orissa on a small scale. Recently, ICAR New Delhi has identified three Bt cotton varieties viz. PAU Bt 1 was developed by PAU, Ludhiana, and F1861and RS 2013 by CICR, Nagpur for cultivation in Punjab, Haryana, and Rajasthan.
Monsanto also released genetically modified potato ‘NewLeaf” in 1995, imbued with a pest repelling gene. But the NewLeaf potato never captured more than 5% of the seed market in the US and Canada, as farmers either did not want to pay the premium prices for seed set by Monsanto or pulled into the GM foods controversy sweeping the nation. McDonald’s Corporation, one of the few potato buyers eventually backed out in 2000 forcing Monsanto to pulled the NewLeaf potatoes from the market in 2001.
There is a wide utilization of transgenic crops producing Bt toxins globally for the production of transgenic cotton, tomato, potato, maize, brinjal, soybean, and tobacco which can be summed up as follows:
2. Disease Resistance
Viral, bacterial and fungal diseases cause major losses in productivity and quality of agricultural crops. Chemical methods are available for the control of fungal diseases and to a lesser extent for bacterial diseases but there are no economically effective chemical controls for viral diseases except to control vector species. Disease resistance has been a wonderful strategy in which a disease-resistant gene is introduced in the plant to create a pathogen-resistant GM variety of plants. The approach is to identify those genes or gene products that when present in a specific plant variety will interfere with the normal functioning of the plant leading to resistance to a specific disease. Plant pathogen resistance is a result of the formation of a number of biomolecule compounds like PTI/ETI including antimicrobial peptides and ribosome inhibiting proteins and enzymes of plant defensive secondary metabolites.
In 1989, the University of Hawaii, in collaboration with Cornell University genetically modified the Papaya variety ‘Solo‘ to create GM varieties: SunUp, Laie Rainbow, and Gold are resistant to Ringspot Virus. In America, GM papaya was adopted rapidly after its commercial production in 1998 when the Administrative The Committee of the Papaya (CAP) negotiated access to the various patents required and began distributing seeds to farmers. GM papaya ‘Huanong No. 1‘ has been authorized for marketing in China since 2010.
The genes Rep-TrAP-REn and BC 1 isolated from the Brazilian bean golden mosaic geminivirus (BGMV-BR) were cloned in antisense orientation under the transcriptional control of the CaMV 35S promoter. Antisense is a gene in which the opposite strand serves as a template during transcription. This construct was used to transform the common bean (Phaseolus vulgaris L.) into a transgenic plant using the biolistic method. The plants from R3 and R4 generations were challenged by inoculation with a BGMV-BR viruliferous whitefly population; out of the four transgenic lines tested two had both delayed and attenuated viral symptoms.
Honey Sweet Plum was genetically engineered against the plum pox virus by inserting the PPV-CP (plum pox virus coat protein) gene. Hypocotyl slices were transformed with the CP gene of PPV-CP following co-cultivation with Agrobacterium tumefaciens (binary vector) containing the plasmid PGA482GG/PPVCP-33. This binary vector carries the PPV-CP gene construct, as well as the chimeric neomycin phosphotransferase and beta-glucuronidase genes.
A variety of red rot-resistant transgenic sugarcane containing B-1,3-Glucanase genes from Trichoderma has been developed in China. Bioassay of transgenic sugarcane has shown restriction to the development of the fungal hyphae and even lysis in parenchymatous cells storing sucrose in contrast to the susceptible plants where sucrose has been depleted. Colletotrichum falcatum is an important fungal pathogen that causes red rot by targeting sucrose storing parenchymatous cells in sugarcane. Even the expression of the transgene was up-regulated after infection and was successfully transmitted to the second generation.
Tea plantation also shows great losses in yield as well as in quality due to diseases caused by Colletotrichum sp. A new anthracnose resistant tea variety ‘ZC108‘, has been developed showing differential expression of genes like MADS-box and NBS-LRR which are involved in disease resistance in China.
3. Herbicidal Resistance
Weeds compete for space, nutrients, and sunlight which can ultimately lead to significant yield losses in the crop and cause contamination of the bulk seed, if they are present at harvest. Control of weeds through herbicide application during the crop growing season has a significant impact on the quality and quantity of grain produced. Plants resistance to the herbicide can be achieved by introducing a specific gene like Gox (glyphosate oxidase) isolated from Achromobacter or aro A gene from Salmonella typhimurium into a glyphosate EPSP (5-enolpyruvylshikimate-3-phosphate) synthase of the shikimic acid pathway. The EPSP inhibitor herbicides are readily absorbed through plant foliage and translocated in the phloem to the growing point, which detoxifies the herbicide. EPSP inhibition leads to depletion of the aromatic amino acid tryptophan, tyrosine, and phenylalanine that are needed for protein. synthesis.
Using the technique glyphosate-resistant transgenics of wheat, tomato, potato, sugar beet, tobacco, soybean, corn, canola (rapeseed), alfalfa, sorghum, and cotton have been developed. Glyphosate-resistant transgenics are also called roundup ready crops as these are genetically modified to be resistant to the herbicide Roundup (brand name of glyphosate traded by Monsanto). Because the Roundup Ready varieties are resistant to glyphosate, the herbicide can be used in the fields to eliminate unwanted foliage and there is less need for ploughing. In Amaranthus tuberculatus, Glyphosphate resistance has been found to be hindered with good large-scale, spatial management practices but are exacerbated with poor management strategies.
Dow’s new-fangled seeds contain a gene from a soil bacterium that codes for a protein that decomposes 2,4-D into harmless chemicals. Dow AgroSciences produces these new GE crops under the brand name ‘Enlist’ which will be stacked with glyphosate resistance and heading for approval. Basically, the idea is to replace crops that have become resistant to glyphosate with crops that become resistant to 2,4-D.
On the other hand, Sulphonylurea-resistant tobacco plants are produced by transforming the mutant ALS (acetolactate synthetase) gene from Arabidopsis. Atrazine-resistant transgenic tobacco plants have been produced by transferring QB protein of photosystem II from mutant Amaranthus into tobacco.
4. Resistance to Abiotic Stresses
Abiotic stresses such as drought (water deficit), excessive watering (water-logging/ flooding), extreme temperatures (cold, frost, and heat), salinity (sodicity) and mineral (metal and metalloid) toxicity negatively impact growth, development, yield, and seed quality of crop and other plants. The development of resistant crops by genetic engineering requires the identification of key genetic determinants underlying stress resistance in plants and introducing the genes into the crops. Molecular control mechanisms for abiotic stress resistance are based on the activation and regulation of specific stress-related genes. These genes are involved in the whole sequence of stress responses such as signaling, transcriptional control, protection of membranes, proteins, and free-radical and toxic compound scavenging.
A group of Indian, Chinese, and Canadian scientists has developed transgenic rice that gives high yields even under severe water deficit. The transgenic has been developed by transferring a gene from Arabidopsis thaliana into a variety of Indian rice ‘Samba Mahsuri’. Putting the Th gene into the rice increased its height, length of the panicle that encloses the grain, efficiency of photosynthesis, chlorophyll content, and water use efficiency. In normal rice, chlorophyll content required for plants to grow reduces under stress conditions like drought, which in turn hits the yield. Thus, the transgenic rice maintains high chlorophyll content even under water-deficit conditions and therefore performed better.
5. Improved Quality
To improve the quality characteristics of the plant, genetic engineering techniques are mainly focused upon developing plants with a longer shelf life of fruits, reducing the starch level and production of novel carbohydrates, modification of storage proteins, improving the amino acid compositions, improving fatty acid compositions and increasing nutritional factors.
The first genetically modified antibiotic-resistant tobacco plant was produced in 1983. While the first genetically modified food approved for release was ‘Flavr Savr‘ tomato developed through inserting antisense copy of PG (polygalacturonase) gene into its DNA by Calgene (later on Monsanto) in 1994. Through genetic engineering, Calgene slowed down the ripening. process of the tomato; as fruit cell wall pectin of the transgenic tomato degraded more slowly than the normal one and thus preventing it from softening while still allowing the tomato to retain its natural color and flavor.
During 1995-1996, Calgene’s high laurate variety was the first GE rapeseed commercially grown in Georgia as a winter crop. Its oil is considered a value-added product. The modified variety was grown under contracts from Calgene which purchased the seeds and markets its oil under the brand name ‘Laurical‘. Calgene had hoped that Laurical would prove to be a good substitute for cocoa butter in the US. However, high prices and other undesirable compositional qualities have limited its use in food products and it has found a small market.
GM musk melon ‘Cantaloupe‘ with delayed ripening and extended post-harvest life has been developed through the production of S-adenosylmethionine hydrolase (SAMase) the enzyme which leads to altered ethylene biosynthetic pathway. A gene derived from E. coli bacteriophage T3 encodes an enzyme capable of degrading SAM has been introduced in the musk melon genome using a standard binary vector. As both SAM and ethylene play a number of important roles in normal plant growth and development, a synthetic promoter has been designed to restrict SAMase expression in the ripening of cantaloupe.
‘Arctic Apples’ having non-browning character developed from Granny Smith and Golden Delicious became the first genetically modified apple for sale in the United States of America in 2015. Developing non-browning Arctic apples relies upon a technique called RNA interference (RNAi) or Post Transcriptional Gene silencing. The RNAi process is accomplished through the use of a transgene that uses gene sequences that reduces the expression of polyphenol oxidase (PPO). Thus, preventing enzymatic browning of the fruit subjected to mechanical damage such as slicing or bruising i.e. the apple flesh remains its original color. This approach enables silencing of PPO expression to less than 10% of its normal expression but does not change other aspects of the apple.
The storage proteins of major crops are insufficient in one or more of the essential amino acids. So, genetic engineering can be used to improve protein quality by way of an increase in the proportion of specific amino acids within a protein. The genes of the number of plants storage proteins have been cloned and expressed in transgenic plants, for example, zein genes of maize, B1 hordein gene of barley, glutenin genes of wheat, and glycinin and conglecene gene of soybean. Similarly, starch-like Amylose stored in tissues of fruit, seeds, and tubers could also be modified or altered through genetic engineering techniques. Amylose content of grain starch in seeds of transgenic rice plants can be reduced by inhibition of granule-bound starch synthase (GBSS).
Genes for lipid metabolism can be cloned for which mutants (fad E, fad F, fad) are available in Arabidopsis. Analysis of these mutants showed that overexpression of cloned fad E and fad F in the transgenic plants could result in highly unsaturated oil. Similarly, an increased level of long-chain fatty acids should be possible by overexpression of fad 1. Scientists at Calgene (now Monsanto) added a gene from the California bay-plant (Umbellularia californica) in rapeseed-canola, that increased the level of medium-length fatty acids in particular laurate. High-laurate canola provides a new domestic source of economically important oil and is similar to coconut and palm oil. Because the nutritional content of the oil is altered significantly. the Federal Department of Agriculture (FDA) of the United States requires products from this GE variety to be labeled as ‘high laurate canola’ although it was developed mainly for industrial purposes and not for food uses.
However, the expression of modified storage proteins or starch in transgenic plants is still in its infancy i.e., information on the effect of overexpressing protein or starch, rich in particular amino acid on amino acid pools or starch or other physiological factors in transgenic plants are lacking. Protein or starch quality is not the only parameter of importance but the interaction in changes in protein or starch quality or lipid and their quantity with changes in oil or starch also needs to be examined to provide a useful product.
Transgenic rice exhibits increased production of ß-carotene as a precursor of vitamin A in the endosperm leading to yellow color seeds. The patented key technology for Golden Rice production was invented by Prof Emeritus Ingo Potrykus of Swiss Federal Institute of Technology. Zurich and Prof Peter Beyer of the University of Freiburg, providing access to a package of ancillary technologies required to engineer the trait into rice; such ‘Yellow or Golden Rice‘ may be a useful tool to treat the problem of Vit ‘A’ deficiency in young children living in the tropics.
Issues With GM Foods
GM crops are grown today or under development, have been modified with various traits. These traits include improved shelf life, disease resistance, stress resistance, herbicide resistance. pest resistance, production of useful goods such as biofuel or drugs, ability to absorb toxins, and for use in bioremediation of pollution. While, theoretical discussions have covered a broad range of aspects; the three main issues debated are the potentials to provoke outcrossing and mixing, allergenicity, and ethical issues.
1. Outcrossing and Mixing
Allowing GE crops to be grown close to organic or non-GE conventional crops (open-pollinated) increases the risk of genetic cross-contamination, as pollen from GE crops has the potential to drift onto organic or non-GE crops. The migration of genes from GM plants to conventional crops or wild related species (referred to as outcrossing), as well as mixing of crops derived from conventional seeds with GM crops, may have an indirect effect on food safety and food security.
Cases have been reported where GM crops approved for animal feed or industrial use were detected at low levels in the products intended for human consumption. Several countries have adopted strategies to reduce mixing including a clear separation of the fields within which GM crops and conventional crops are to be grown.
2. Allergenicity
There is a chance of allergenic responses in an individual after contact or consumption of GM foods or transgenics. Gene transfer from GM foods to cells of the human body in the gastrointestinal tract would cause concern if the transferred genetic material adversely affects human health. This would be particularly relevant if antibiotic resistance genes, used as markers when creating GMOs, were to be transferred. Although the probability of transfer is low, the use of gene transfer technology that does not involve antibiotic resistance genes is encouraged.
While foods developed using traditional breeding methods are not generally tested for allergenicity, protocols for the testing of GM foods have been evaluated by the FAO and WHO of the United Nations. As a matter of principle, the transfer of genes from commonly allergenic organisms to non-allergic organisms is discouraged unless it can be demonstrated that the protein product of the transferred gene is not allergenic. No allergic effects have been found relative to GM foods currently available in the market.
3. Ethical Issues
Modern agriculture has offered the potential for sustainable feeding of the world’s increasing population. Although genetically modified (GM) foods have facilitated increased yields and reduced pesticide usage, these are divisive amongst policymakers, scientists, and even the consumers concerning their potential environmental, ecological, and health threats. The ethical standards in concern include beneficence, fair dealing, and sovereignty. So, the use of GM technology in food supplies has been encircled by ethical concerns and situational judgments.
The production and consumption of GM foods have been involved in controversies. Arguments from proponents share that GM foods are the only representatives for overcoming the shortage of food supplies to the ever-growing world population based on the reports from the scientists showing no harm from GM food consumption while opponents are feared from the impending negative impact of GM food sources. Though, GM food is one of the most scrutinized food types from a safety perspective; some risks to the environment and ecosystems like the evolution of herbicidal resistance can arise during the cultivation of GM crops. So, there is an influence of Scientific and political debates on legislation and the eventual risk appraisal system. Also, regulation of the production and consumption of GM foods are governed by a harmonized framework of several agencies at the national and international levels throughout the world. Although there have been some expressions of concern about biosafety and health hazards associated with GM crops, there is no reason to hesitate in consuming genetically engineered food crops that have been thoughtfully developed and carefully tested.
Read More Topics of the Same Course – ABT 5211 – Food Safety and Standards
