Developments in Plant Sciences Learning Objectives

Transcription

1 Chapter 16 Developments in Plant Sciences Learning Objectives 1. Explain the importance of DNAbased biotechnology in agriculture Offical 2. Explain the fundamental concepts of genetic engineering in plants 3. Discuss economically important plant traits that have been modified or enhanced by biotechnology TMG 4. Discuss the use of tools and techniques used for the genetic modification of plants 5. Discuss some of the social and ethical issues related to the genetic modification of plants Instructor Copy

2 Developments in Plant Sciences Figure 1. Crop Research in Soybean Plant domestication was developed when humans noticed desirable traits in wild plants and began cultivating for those specific traits. One of the earliest known examples of this was the cultivation of wheat and barley in the Middle East in the eighth millennium BC. Another early example of this was the domestication of rice in China and southeastern Asia in 5500 BC. Essentially, during those times, and up until the relatively recent past, people were selecting good genes and dismissing bad genes without even knowing that something called genes existed. With this early form of active selection, agriculture developed. Agriculture was thought to have developed 10,000 to 12,000 years ago in the regions of present day Syria, Turkey, Iraq, Iran and northern Egypt. The Beginning of Plant Breeding Present day agricultural methods have improved tremendously since the first days of agriculture. Many advances in plant breeding have come as a result of research performed in the 19th century by a Czechoslovakian monk named Johann Gregor Mendel. In 1866, he published an important work on classical genetics. Most people remember the Mendel s peas lesson from school days past. In this experiment, Mendel crossed plants with contrasting traits, for example short versus tall. He then hypothesized that elements were responsible for contrasting traits and that these elements, now known as genes, do not blend to form a mixed trait in the next generation. Rather, the elements, or genes, act independently of one other. His experiments with crossing pea plants and analyzing the physical traits of offspring laid the foundation for our present day understanding of how genes are transmitted from one generation to the next. For his contributions to the field, Mendel is known as the father of genetics. As stated above, Mendel s research laid the foundation for plant breeding. Plant breeding is when two different plant lines with favorable characteristics are crossed and then have their offspring screened for the desired characteristics-thus the term hybrids. As plant breeding continued to develop as a means to change crop genetics, it laid the foundation for modern day plant biotechnology. Introduction to Biotechnology Biotechnology is the modification of living organisms to create useful products. Plant biotechnology involves the altering of genes and plant cells for the purpose of modifying and enriching economically important traits. The term biotechnology is relatively new, but humans have been applying the principles of basic biotechnology for hundreds of years. The utilization of microorganisms to make bread, wine and beer is a simple form of biotechnol- Hybrids Many of the highest-yielding varieties of crops in the world, such as corn, are hybrids. Modern-day corn was generated through years of breeding from its ancestor teosinte, which still grows in the highlands of Mexico. While teosinte is a different-looking plant than corn, they are both members of the same biological species, Zea mays. In contrast to corn, teosinte is a spindly grass plant without ears. Tennessee Master Gardener Handbook 464

3 A Timeline of Biotechnology 10,000 BC: Yeast is used to make food items such as wine and bread 8,000 BC: Early farmers begin cultivating the land and saving seeds to grow for the next season 1866: Gregor Mendel publishes his work on the heredity of traits in plants 1908: The first corn hybrid is produced in the USA by G. H. Shull of the Carnegie Institute 1919: Hungarian engineer Karl Ereky coins the term biotechnology 1953: Watson and Crick propose the double helical structure of DNA 1982: The first transgenic plant is produced 1988: Cornell scientists invent the gene gun 1994: The first genetically modified food crop, the FlavSavrTM is approved by the FDA for human consumption : Biotechnology-derived soybean, corn and cotton are approved for sale and cultivation in the United States 2003: Over 38 trillion transgenic plants have been grown in the United States since : The National Center for Food and Agriculture Policy reports that the use of biotechnology in agriculture generated a 2.5 billion dollar increase in farm income, with 14 billion more pounds of food produced and 163 million pounds less of pesticides applied in the fields ogy. However, today there is the capacity to practice biotechnology on a much more controlled and precise scale. Many scientists believe that in the future, biotechnology will be necessary to feed the world s growing population without harmful effects on the environment. The Green Revolution The Green Revolution of the 1960s and 1970s was an effort by the Rockefeller and Ford Foundations to boost crop production in developing countries. Dr. Norman Borlaug2, an American scientist, played a pivotal role during this time by developing high-yielding varieties of dwarf wheat and other crops by conventional breeding. Simply, the result of his experiments was that millions of lives were saved from starvation in India, Pakistan and other countries that routinely suffered from terrible food shortages. Dr. Borlaug was awarded the Nobel Peace Prize in 1970 for this astonishing achievement and service to humanity; the only time a plant scientist has won this prize. Since the Green Revolution, world population growth has increased exponentially, and is expected to exceed 10 billion people by Unfortunately, agricultural production has grown at a much slower rate. Thus, in the future, it will be a challenging task to meet the dietary needs of the earth s population. Although conventional plant-breeding methods have increased crop yields, there are limitations. For example, it can take up to 10 years to breed out undesirable traits, a process called backcrossing, to develop a desirable hybrid line. Additionally, there are limits to the available genes resident in each crop that can be manipulated for crop improvement. The bright side is that science is progressing. DNA-based plant biotechnology can reduce the time it takes to create crops with new or improved traits. In this approach, a gene that controls a desired trait is taken from one organism and transferred into a crop plant s genetic make-up, or genome. Because the technique is precise, it takes less time to release a crop with the desired traits. As did the first revolution, DNA-based biotechnology is helping to revolutionize agriculture. Plant biotechnology uses well-understood lab techniques to transfer a gene or genes from any organism into plants. The new genes then essentially become part of plant genome and are inherited to offspring, just as if they were plant genes all along. To summarize, while the Green Revolution primarily addressed crop yield; the biotechnological revolution has the potential to improve food quality as well as yield. Tennessee Master Gardener Handbook 465

4 Figure 2. Difficulties of Plant Breeding Traditional plant breeding is time-consuming and labor-intensive which is a problem as the pressure mounts on agricultural producers to create more food for more people in less time. Trait Enhancement and Modification of Plants Plants are continually exposed to both biotic, living, and abiotic, non-living, stresses. From these stresses, plants have no option but to adjust to the stress or die. Reports suggest that there can be between percent loss in crop productivity due to biotic and abiotic stresses. One of the goals of plant biotechnology has been to develop stress-tolerant plants. Specifically, researchers are developing plants that have increased tolerance to: drought, salt, cold, insects, diseases and herbicides. They are also developing plants that have: traits for human health, increased nutritional quality, the ability to developed into a vaccine and modified flowers. Dr. Max Cheng, University of Tennessee Researcher, genetically modifies plants that have invasive characteristics to be sterile. Drought and Salt Tolerance Drought is one of the major problems responsible for damage to crops and loss of productivity. Fortunately, in some plants, scientists have identified chemicals known as osmoprotectants that help protect plants against drought stress. Biosynthetic pathways of some of the osmoprotectants have been identified and plants have been modified to produce osmoprotectants. However, drought tolerance has proven to be a difficult modification because a plant that is drought-tolerant in the lab might not be tolerant in the field. Cold Tolerance Low temperatures may cause stress for plants not tolerant to cold conditions. In an effort to better understand the physiology behind the effects of cold on plants, scientists have been studying plants that thrive in cold climates. They have discovered that some freeze-tolerant plants form ice crystals surrounding the outside of their cells. This layer of ice appears to help protect the inside of the cells from forming ice crystals that would cause death. Scientists believe that cold-acclimated plants sense low temperatures and turn on specific genes like those responsible for ice barrier formation. Efforts have been made to incorporate cold-protection genes into crops such as canola, potato and flax. Recently, scientists modified the plant cell membrane to improve freeze-tolerance, indicating that an effective, commercial, freeze-tolerant plant is feasible. Insect Resistance From biblical locust plagues to boll weevils, farmers have experienced large economic losses from crop-eating insects. To control insects, farmers often resort to chemical insecticides. Unfortunately, many insecticides are harmful to human health. Additionally, the accumulation of insecticides in ecosystems can be problematic. As a result, there have been efforts worldwide to produce genetically engineered crops that are resistant to insects. In other words, to produce plants that produce their own insecticide. The most successful development so far has been the creation of Bt plants. Bacillus thuringiensis, better known as Bt, is a naturally occurring bacterium found in the soil that produces a toxin lethal to certain types of insects. Genes coding for Bt toxins are Tennessee Master Gardener Handbook 466

5 well characterized and have been transferred into several types of plants. The amazing characteristic of Bt toxins is their ability to target specific pests. For example, one type of Bt toxin kills only specified caterpillars and no others. Bt toxins do not harm people, birds, fish or wildlife. Many organic farmers and homeowners have used Bt sprays to control insects for about a half a century. Thus, much is known about the effects, and it is considered safe. When the gene responsible for producing Bt toxin protein is incorporated into crop plants through genetic engineering, the Bt gene triggers production of a toxin. When the insect larvae feed on transgenic Bt plants, the toxin enters the gut of the insect, binds with specific Bt receptors, causes gut leakage and eventually death. This technology has been very successful in protecting plants against insect damage. For example, more than half the cotton and nearly one third of the corn grown in the U.S. produce Bt. Bt technology has successfully controlled European corn borer and cotton boll worm, decreasing the need for insecticidal sprays, especially in cotton. Biotechnology vs. Insecticides Millions of gallons of chemical insecticide spray have been replaced annually in the United States due to biotechnology yielding an astounding environmental benefit. Disease Resistance Plants are continuously challenged by pathogens such as bacteria, viruses and fungi. To survive these attacks, plants have developed their own defense systems. However, many of these are weak. Strong disease resistance does exist in nature, but not always in the desired plants. Therefore, farmers and gardeners must apply chemical pesticides when desired plants are infected with diseases and unable to defend against them. Despite advances, disease resistant modifications to crops have been slow to succeed. Plants like rice, tobacco and canola have been modified with plant genes to help protect them against a type of soil-borne fungus called Rhizoctonia solani. Additionally, some tomato plants have been modified for resistance against tobacco mosaic virus (TMV) and potato and rice were engineered for resistance against nematodes. However, none of these applications have made it to commercial release for various reasons. The most successful disease-resistant plant produced through biotechnology is a virus-resistant papaya, presently grown commercially in Hawaii. Produced by a research team led by Dr. Dennis Gonsalves, this virus-resistant variety is believed to have saved the Hawaiian papaya industry. Herbicide Resistance Weeds rank highly as one of growers worst enemies, and herbicide application is the most popular method for their control. Herbicides are applied either to the soil or sprayed onto plant leaves, depending on the types of weeds that need to be eradicated. The main problem with herbicide application is associated with the residual effects on the soil. Residual herbicide in the soil can damage other sensitive crops in the crop rotation system as well as contribute to pollution. Herbicide-tolerant crops are useful because they allow farmers to control a wide range of weeds with no damage to the crops themselves. Non-selective herbicides can be applied to fields planted with transgenic herbicidetolerant crops without any damage to those crops. Examples of herbicide tolerant crops are Roundup Ready cotton and Roundup Ready soybeans. Roundup Ready soybeans are grown in more than two-thirds of the soybean fields in the U.S. Traits for Human Health Stress tolerance is only one aspect of useful crop modification being researched by scientists. There is also a growing interest in creating crops with enhanced nutritional qualities. In addition, some researchers are finding ways of providing edible vaccines. Edible Vaccines Vaccines are molecules that trigger the human immune system to attack invading pathogens. The development of vaccines has changed the way people experience disease. Because of vaccines, smallpox, polio and whooping cough are virtually non-existent in the U.S. However, Tennessee Master Gardener Handbook 467

6 Trans Fats Trans fat is monounsaturated or polyunsaturated fat that is altered by partial hydrogenation. The process of partial hydrogenation forces oils that are naturally liquid at room temperature to become solid, thereby modifying the fat so that it is similar to saturated fat. While trans fatty acids are considered unsaturated by chemical definition, the transformation is so severe that trans fats cannot be legally labeled as monounsaturated or polyunsaturated on packages. However, the FDA only requires that saturated fat be labeled on food products and limits the extent to which items can be labeled as low cholesterol. Trans fat does not need to be labeled. Therefore, a company is able to label their product cholesterol free when in reality, the product may contain a substantial amount of cholesterol by means of trans fat. In response to this, laws regarding labeling for trans fats are being examined. due to the lack of infrastructure and prohibitive costs in many parts of the world, vaccine availability may be limited or completely unavailable to some individuals. In developing countries, people face life-threatening diarrheal diseases at a much higher frequency than in the U.S. Therefore, there is great need to develop vaccines against such diseases and deliver them economically. Perhaps food plants can help. Possibilities exist to produce vaccines in plants by genetically modifying them with antigens that, when ingested, deliver the vaccination. Antigens in the plants would trigger the formation of antibodies in human cells, like vaccines, providing immunity and thus eliminating costly vaccination by injection. Currently, tobacco and lettuce plants have been modified with a hepatitis vaccine and vaccines against footand-mouth and diarrheal diseases are currently in development. Enhanced Nutritional Quality Nutritionally enhanced food crops may be particularly useful in developing countries where the availability of nutritious foods is a serious issue. As an illustration, night blindness is a common condition found amongst children who are deficient in vitamin A. Dr. Ingo Potrykus, from the Swiss Federal Institute of Technology, and his colleagues developed a type of rice with high vitamin A content, popularly known as golden rice. This rice was genetically modified to produce beta-carotene, a precursor of vitamin A. The name golden rice comes from the yellow-gold color of the enhanced rice grain. The current goal is to incorporate golden rice into the local rice breeding lines of developing countries at no cost to their farmers. If the effort to distribute and cultivate golden rice in developing countries is successful, it will be an outstanding example of biotechnology s application for humanitarian purposes. Other crops have also been genetically modified for enhanced nutritional qualities. Canola plants were engineered to contain no trans fats-unsaturated fats. Trans fats are a current topic of concern as medical studies have shown them to be responsible for negatively affecting the good fat levels in humans. Canola Oil: The Good the Bad and the Ugly Peanut oil comes from peanuts and soybean oil comes from soybeans. However, there is no such thing as a canola. Canola is a marketing name derived from Canadian-oil. Canola oil comes from the rapeseed plant (Brassica napus). It belongs to the mustard family, which also includes turnips and broccoli. As we know it today, canola oil is the result of the hybridization and genetic modification of the rapeseed plant to breed out its undesirable taste and its hazards to health. Because canola oil hydrogenates better than corn or soybean oils, it is often the first choice of processors. However, when it is hardened through hydrogenation, as it often is when used in food processing, the trans fat level can go as high as 40 percent. This is desirable for the food industry because higher levels of trans fat translates to longer self life for processed food, and greater profits for the food industry. For more information on this topic, please visit the Natural News website. The link is posted at the end of this chapter. Tennessee Master Gardener Handbook 468

7 On the Lighter Side-- Altered Flowers Horticultural crops have also been engineered for targeted trait enhancement and modification. An Australian company named Florigene was able to clone a blue gene and genetically transform carnations to produce blue petals. According to Florigene, this was the first case of any carnation flower expressing a blue color hue. They credit themselves with having produced the world s first genetically modified flower. Regulating Transgenic Plants Either university or governmental officials regulate all biotechnological manipulations. In every university, there is an institutional biosafety committee that oversees laboratory work. This committee is comprised of experts who ensure that experiments are done safely. The University of Tennessee is no exception in this regard. If researchers or companies wish to test transgenic plants in the field or ship them between states, the USDA Animal and Plant Health Inspection Service (APHIS) becomes involved, along with the Tennessee Department of Agriculture. Applications must be filled out, and certain restrictions often apply. Additionally, agriculture officers frequently inspect field sites to assure that correct procedures and safeguards are in place. If Bt genes or other pesticidal genes are put into plants, then the EPA has regulatory authority as well. The FDA and EPA make sure transgenic food is safe to eat. As indicated by the above information, there is a long chain of procedures that must take place before any transgenic plant is grown commercially. In fact, it often takes several years to gain approval, and sometimes certain plants are not approved. It has been often said that transgenic plants are the most tested plants in the history of the world. Figure 3. Regulating Transgenic Plants Current and Potential Benefits for Plant Biotechnology Current and potential benefits of plant biotechnology include: Edible vaccines Enhance nutrition Aesthetics Resist herbicides Resist diseases Resist drought Resist Insects Increase salt tolerance Increase cold tolerance Increase the genetic diversity of species populations Increase to the efficiency of the ecosystem services provided by the other organisms. For example, modifying trees to have hardier root systems to withstand frequent flooding Public Perception of Transgenic Plants There is an ongoing debate regarding the development of genetically modified crops, their consumption by humans and their potential ecological effects. The major controversies surrounding genetically engineered crops and foods commonly focus on either: the longterm health effects for anyone eating them; environmental safety; labeling and consumer choice; intellectual property rights; ethics; food security; poverty reduction; environmental conservation; and potential disruption, or even possible destruction, of the food chain. Some Tennessee Master Gardener Handbook 469

8 Figure 4. Crop breeding of Switchgrass for Biofuels Production in Tennessee Reasons People May Oppose Plant Biotechnology: Lack of information Perceive it as unnatural Ethical reasons Environmental concerns Religious reasons Perceived potential for significant unforeseen consequences unease is due to a general lack of understanding of the science behind the technology. Most information the public receives about genetically modified organisms (GMOs) is spun by media frenzy and environmental activist organizations that are opposed to GM plants. Those opposed to plant biotechnology argue that DNA-based genetic modification of plants is abnormal, or going against nature. However, virtually none of the plants we eat are genetically natural. Most of the cultivated crops we consume today are the result of 10,000 years of selection, domestication and breeding in other words engineering. Corn s ancestor, teosinte, has few similarities with modern-day cultivated corn. This example proves how humans have manipulated the genes of wild plants for thousands of years to develop food crops with better qualities. Another example is the tomato. The large, red tomatoes we buy at the grocery store and grow in our gardens exist nowhere in nature. They are the result of years of breeding and selection. Wild tomatoes are tiny greenishyellow things that most people would not care to eat. Consider the many choices of fruits and vegetables found in grocery stores today. These foods could be considered unnatural in the sense that they are also the results of thousands of years of breeding, crossing and moving genes from one population to another. Some concerns about genetic modification are legitimate. For example, there is a concern that crops modified to resist herbicidal sprays may pass the trait for herbicide resistance to weedy relatives, resulting in new weed problems. Research is currently being performed in this area to conclude how likely it would be for this to occur. Indeed, transgene flow from crops to wild relatives has been one of the biggest concerns among scientists and environmentalists. Thus, it is doubtful that crops with noxious weedy wild relatives will be engineered. No one in biotechnology wants to create new weed problems. Summary People eat products from genetically engineered foods every day. For example, Americans have been consuming genetically modified soybean oil and corn products for some time now. To date, there have been no scientific reports indicating that genetically modified foods pose a threat to human health. Additionally, the application of biotechnology in agriculture promises sustainable production with higher yields and less poisonous chemicals in the food and the environment. However, despite its many current and potential benefits to the earth and to humans, biotechnology is not a cure-all. Also, it has not been universally understood and accepted by the general populace. There are social, political and economic issues associated with the use of any new technology. Everyone in the world might someday enjoy the benefits of plant biotechnology, but seeds produced via patented technology may be initially out of reach for poor farmers in the developing countries. As biotechnology progresses, however, it will certainly enhance agricultural productivity and sustainability around the world by providing environmental and dietary benefits. This chapter has taught you the importance of DNA-based biotechnology in agriculture, the fundamental concepts of genetic engineering in plants, the economically important plant traits that have been modified or enhanced by biotechnology, the use of tools and techniques used for the genetic modification of plants, and some of the social and ethical issues related to the genetic modification of plants. Tennessee Master Gardener Handbook 470

9 Terms to Know Abiotic Biotic Biosafety Biosynthetic pathways DNA Gene Genome Osmoprotectants Transgene flow Transgenic plants Yield Test Your Knowledge 1. Who was the father of genetics and when did he publish his works on classic genetics? 2. What is the precursor to plant biotechnology? Give an example of a modern crop. 3. What is the amazing characteristic about insect resistant Bt developed trangenially? 4. What is golden rice? 5. Name two reasons one may oppose plant biotechnology. Resources America Society of Plant Biologists aspb.org Council for Biotechnology Information whybiotech.com Greenpeace greenpeace.org National Agricultural Library. Contains various outside links for more information about genetically modified crops nal.usda.gov/bic National Center for Food and Agriculture Policy ncfap.org: Natural News naturalnews.com/026365_canola_oil_ food_health.html United States Department of Agriculture usda.gov/agencies/biotech Tennessee Master Gardener Handbook 471