Keywords: Bt-crops, Cry-toxins, transgenic plants, GM-crops, genomic, ... last 20 years, transgenic plants with insecticidal activities, are being used worldwide.
Evolution and Importance of Bt-crops A review paper. Faizullah Khan, College of Marine and Agriculture Sciences, Sultan Qaboos University, Sultanate of Oman
Keywords: Bt-crops, Cry-toxins, transgenic plants, GM-crops, genomic, proteomic, Bacillus thuringiensis. Abbreviations: GM, genetically modified, EPA, Environmental Protection Agency, Cry, crystalline, Bt, Bacillus thuringiensis Introduction: Genetically modified crops, is well-known term in the recent years. It refers towards the crops with added characteristics. There might be physical stress tolerance, for example against salinity, drought resistance etc. Some plants have extra nutritional values, like golden rice, providing beta-carotene, which is a precursor for Vitamin-A. Plants like GM tobacco can produce antigens for pharmaceutical purposes. Advancement on environmental aspects of GM crops have been known for over a couple of decades. Bacillus thuringiensis or Bt crops, are known for their pest-resistance properties. It helps in reduction of pesticide applications and thus serves as an environment-friendly member of the GM crops. Bt crops have Bt-gene, incorporated in their genome, and expressed into a crystalline protein, called “Cry-Toxin”, which is the main pesticide for insects. Usage of Cry-toxin is known since the beginning of 19th century. It was applied via dispersion over the field. After the revolution of genetic engineering, the same gene was used to produce Bt-crops. It is commonly known as harmless and highly target specific. In addition to its advantages, it has also certain limitations like gene pollution and expensive to adapt etc. Historical Background: In 1901, a Japanese scientist, name Shigetane Ishiwata was able to isolate Bt from silkworm larvae. It happened accidently, as an investigation of the cause of large number of silkworm larvae was carried out. Later on, in 1911, a German scientist, Ern Berliner recovered the specific strain from dead flour moth larvae. It was carried out in a state, named Thuringia, so the bacterium was named after the place. The Bacterium, under stress condition forms a cyst and releases endotoxins, called cry-toxins. The parasporal cyst formation and insecticidal activity was identified by Thomas Angus in 1953. Later, in 1955, Philip James and Hannay made it clear that the activity is carried out by protein, which makes the parasporal structure. In 1938, France produced Bt sporine for the first time on commercial scale against flour moths. United States adapted the commercial use of Bt in 1958. For the first Bt was registered in 1961 as Bioinsecticides with Environmental Protection Agency. For the last 20 years, transgenic plants with insecticidal activities, are being used worldwide. A statistical data shows that over 50% of cotton and around 40% of the corn grown in the US are Bt-crops (Muhamed Ibrahim et al. 2010).
When 1901 1911 1938 1953 1955 1961 1996 onwards
What/Who/Where Isolation of Bt from dead larvae of silkworms by Shigetane Ishiwata /Japan Isolation of Bt from dead larvae of Flour Moth by Ern Berliner /Germany Commercial usage of Bt (spore) as insecticide in France Identification of Parasporal Crystals by Christopher Hannay Protein forms Parasporal Crystals by Christopher Hannay Bioinsecticides registered in US, EPA. Worldwide usage and commercialization of Bt crops.
Genomic and proteomic perspective of Bt: Bacillus Thuringiensis is a gram-negative bacterium. During sporulation process, it forms a parasporal cyst. Bacillus Thuringiensis has a gene, named cry-gene. This gene is responsible for the production of Cry-toxin (because of its crystalline form). The expression of this gene occurs during stationary phase of the life cycle. These cry-genes are located on the plasmids of bacterium. There are more than 50 groups and subgroups of cry-genes (Muhamed Ibrahim et al. 2010). There are different types of cry-toxins, classified into classes for nomenclature, for example Cry1Aa, Cry2Aa, Cry1Ab, Cry2Ab, and Cry1Ac etc. Almost all of them share the same major structure. A typical cry-toxin consists of 3 domains, Domain I (forms Ion chain in cell membrane), Domain II (loops the insecticidal toxins), and Domain III (receptor binding and cell membrane binding). Cry-toxins are produced as a monomer. These proteins have higher tendency of forming oligomers, upon reaching the host gut. Mechanism of Action: There are different opinions regarding “mechanism of action” depending on host and cry-toxin type. In some cases, cry-toxin is believed to form oligomer inside the gut of host, leading to lytic pores in cell membrane and ending up in death of the host. Another case suggests that the oligomer kills the host cell by developing osmotic pressure outside the cell and osmolysis. Another case states that binding of cry-toxin to the cell surface causes alteration and acceleration in the cell processes and thus leading to cell death (Muhamed Ibrahim et al. 2010). Role of Transgenic plants in agriculture and biopharming: the demand for improved variety of crops is at all time high now. Population of world is increasing and agricultural lands are being rapidly converted into residential zones. Biotechnological advancements have made it possible to overcome the undernutrition or malnutrition. The new hybrid traits are capable of yielding more than conventional crops. There are various, genetically engineered, fortified crops which provides extra nutrition to the consumer. A very commonly known example of golden rice is a result of those practices (Pervez Ahmed et al. 2012). Sustainability of the plants is as much necessary as its productivity. The plants should have the ability to survive environmental stresses. There might be challenges like, drought, flooding, salinity, heavy metal tolerance, and high/low pH. Plants can be provided with a genome to cope with all or maximum of the challenges. There are certain examples of potato spp. which are considered as drought resistant at maturity. At the time when it reaches maturity, it ceases its metabolism at minimum (Pervez Ahmed et al. 2012).
There might be natural enemies of the plants, like some insects, which needs to be stopped. Natural enemies comprise of a list of organisms, including bacteria, fungi and some insects. Plants are supplied with chemical pesticides, which ultimately end up in pollution causatives. To escape this step, plants are augmented with certain genes which can deal with the natural enemies, with the external intervention. A very common example of this kind of approach is Bt-crops. These plants are supplied with and extra gene that produces toxin against the pathogens and thus avoid the demand of chemical pesticides (Pervez Ahmed et al. 2012). Another more advance application of GM plants is, biopharming. It has other names too, like, farmaceuticle Biotechnology, or molecular pharming. All of them refer towards one concept, i.e. the production of medical products using Plants. Certain plant spp. like tobacco, can produce antigens for hepatitis B. There are plants which has planted gene in their genome and are able to produce edible vaccines, like lettuce contained the gene for HBsAg. Certain spp. of tobacco has already produced enterotoxins which are effective against cholera (Pervez Ahmed et al. 2012). Effect on soil chemistry of GM and Non-GM crops: Bt-crops produce toxins, called Cry-toxins. These toxins are generally frequently dissolved, decayed and decomposed naturally. These toxins are easily washed off by rain and flood, readily soluble in water, decomposed by soil microbes, and breakable by exposing it UV-light. These less viable nature of these toxins enable them a better choice. Cry-toxin has shown least adverse effects keeping in mind the trackrecord. They have been used for over two decades and still counting (Na Liu et al. 2010). In addition to its beneficial aspect, there are some adverse effects as well. In some parts of the world, depending on which part of the word is under discussion. Experiments have been carried out, where a GM crop is compared to non-GM crop. Both of them have been tested in pot and field experiments. Results of the experiments show that the GM crops are adding certain chemicals to the soil. These may not be harmful if they can be utilized easily and readily. The case may be worrisome if already a component exists in excess and the GM crop release more in the exudates (Na Liu et al. 2010). One case study shows that a variety of maize, having Bt-gene, produces Cry1F2 protein and glyphosate. The two compounds are normally frequently degraded by soil microbes. Upon degradation, they yield in increasing soil N, P, and K in addition to rise in pH (Na Liu et al. 2010). Cursor Nitrogen Phosphorous pH
GM maize 11 ppm 6.9 2.4
Non-GM maize 9.6 ppm 6.5 1.1
In regions where the deficiency is a problem, so it can be met by growing those GM crops. In certain researches, it has been shown that the Cry-toxin remain embedded in the soil for around 180 days. After reaching the soil, compound may escape degradation by sticking to the particles’ surface. The insecticidal activity is no more there but viability of the compound is an undesirable characteristic. The experiment was performed in Norway, considering soil from different sites, with pot and field experiment, were checked (Na Liu et al. 2010).
NK603 is GM-maize Three places, Gongzhuling, Dehui and Huadian have been chosen for soil sampling. Comparison is given in the graph.
Effects on Environment: Although, repeatedly discussed but it worth discussing that how the Bt-crops are affecting the ecosystem. Talking about in general, Bt-crops are harmless as compared to chemical pesticides. It is natural remedy and pose insignificant threat towards the ecosystem. Besides those evidences, the fact still remains unchanged that at the end, it kills pests, which is disturbance in the ecosystem. In ecosystem, every living thing has place and plays a certain role. In case there is any missing in one level, the next level is affected. Taking an example of food chain, the insects are placed as primary consumer, after plants- producers. If the number of primary consumers start declining, the ultimate sufferer will be the secondary consumer and so on (Iliana Fontes et al. 2002). Economic Impacts of GM crops: After discussing many aspects of GM-crops, economical point of view also needs to be discussed. As the world returning back to the “all organic” mind set, the GM-crops production on commercial scale has vast business potentials. China is one of those few countries, which is being benefitted from commercializing GM-crops. China is encouraging every sector to promote the production of GM-crops. Chinese agricultural biotechnology is being used as a tool to improve national food security, agricultural productivity, formers’ economy, sustainability and lastly, rise the position of country in international agri-business (Jikun Huang et al.). China began its journey in 1986, by initiating its 863 program. With this, almost every university had an agricultural biotechnology laboratory. By the year 2000, there were 18 GM-crop yielded from those labs,
four of them approved for commercialization. Bt-cotton and Bt-rice are among the most popular GMcrops in China. Biotechnology Research Institute gave a breakthrough in the advancement of GM-crops by producing fungal disease resistant variety of cotton (Jikun Huang et al.). Bt-crops requires less manpower to be taken care of as compared to non-GM crops and thus saves money. On the other hand, it also yields more production than the non-Gm crops. However, it is heavy on pockets when it comes to buying seeds. In the following part, summarized tables for cotton and rice are given.
After detailed examination, it is crystal clear that the only loss in net total is in seed price. If overcome, the GM-crops can be guaranteed “cash crops”. Future Recommendations: After digging into the topic, there are certain questions arising in the minds. If found the answers, it may make the use of Bt-crops safer. Questions are listed below. 1. 2. 3. 4. 5. 6.
What should be done to neutralize toxins after plants’ death. These toxins are no more beneficial. How can the gene pollution be stopped from spreading in the ecosystem? Are there chances of super-weeds production? What should be done to prevent non-target pests? Are there any adverse effects in a long run? What should be the alternate/next strategy if he current available technology is not sufficient for remedy (Reda A. Ibrahim et al. 2014)?
Conclusion: The technique replaces conventional chemical pesticides. It has widespread application. Bt-crops leaves negligible hazard towards soil chemistry. After discussing a variety of aspects, it can be said that it is wise and natural approach towards crop protection. The techniques possess nearly harmless remedy against pests. Long-lasting fruitful results are possible if certain queries are addressed. The technique has a potential to be given a state of industry on national level. References: 1. Bacillus thuringiensis, A genomics and proteomics perspective (Muhamed Ibrahim et al. 2010) 2. Role of transgenic plants in agriculture and biopharming (Pervez Ahmed et al. 2012) 3. Effect on soil chemistry of genetically modified (GM) vs. non-GM maize. (Na Liu et al. 2010) 4. The Environmental Effects of Genetically Modified Crops Resistant to Insects (Iliana Fontes et al. 2002) 5. Economic Impacts of Genetically Modified Crops in China (Jikun Huang et al.) 6. Transgenic Bt-Plants and the Future of Crop Protection (An Overview) (Reda A. Ibrahim et al. 2014)
