How GM Plants Conquered the World

By Donna Houchins - Research & Development Specialist, Romer Labs® USA

Genetically modified organisms (GMOs) are widely used in agriculture to give plants beneficial traits such as herbicide and pesticide resistance as well as quality traits that optimize growth and nutritional content. First trialed in the 1980s, GMO use is now widespread with over 185 million hectares of GM crops planted in 2016.

What are GMOs?

Organisms that are genetically modified have undergone alterations to their genetic material in a process known as genetic engineering. These alterations result in the organism expressing a trait or traits that would not naturally occur in that organism. GMOs currently exist in bacteria, animals and plants, and are used in a wide range of applications including biological and medical research, the production of pharmaceuticals, and agriculture.

Why GMOs?

One of the most widely adopted uses of GMOs is in agriculturally important crops. In these plants, alterations to the genetic material are often accomplished by inserting DNA material from a different organism into the target organism. This results in the plant (and any seeds harvested from the plant) expressing novel traits, such as herbicide or insect resistance, or quality traits such as drought tolerance. For example, genetic modifications have been made so that plants are resistant to herbicides such as glyphosate or glufosinate, allowing a field to be sprayed with the herbicide to kill off weeds without harming the crop.

Genetic modification can also involve the transfer of a trait or traits that allow the plant to produce endotoxins originating from the soil bacterium Bacillus thuringiensis , known as “Bt”. This confers insect resistance.

These endotoxin proteins have been used as sprayon insecticides since the 1920s. They target certain insect species while having no effect on non-target

How to Change the DNA of a Plant

The transformation of plants can be accomplished in several ways. Two of the most common methods in agricultural crops are the use of Agrobacterium tumefaciens, and biolistics (the “gene gun”).

Using the bacterium Agrobacterium tumefaciens provides a natural mechanism for transformation. The bacterium infects injured plant tissue and transfers its Ti plasmid to the plant’s chromosome. The Ti plasmid naturally contains genes that cause the plant tissues to overexpress plant hormones and nutrients for the bacteria, leading to plant tumors. The Ti plasmid may be modified to delete unwanted effects and add desirable traits, along with a selectable marker, which is then integrated into the plant’s chromosome during bacterial infection. However, not all species are susceptible to infection by this bacterium.

Over the course of the last decade, a second method of transformation has grown more popular than Agrobacterium : biolistics, also known as the “gene gun” method. In this method, plasmid DNA is coated onto small tungsten or gold beads. These micron-sized beads are then “shot” into the plant tissue. Some of the cells in the plant tissue may successfully take up the new DNA and integrate it into a chromosome. This method has proven effective for integrating DNA into the cell nucleus as well as into organelles such as chloroplasts, and works in almost all species researched. Other methods that have been used include microinjection and electroporation. species such as humans, wildlife, and beneficial insects. When ingested, these proteins form pores in the mid-gut epithelium of the larvae of susceptible insect species (which feed on the crops, causing damage). This causes paralysis of the gut, and the affected insect stops feeding and succumbs to starvation. Non-target species have no receptors in the gut for the protein, and thus the protein has no effect on them. In addition, GM plants may express quality traits that allow them to be tolerant of environmental conditions such as drought, or to improve their nutritional content.

GMO naming conventions

GMOs may be referred to in one of three ways. First, they may be identified by their event name, which is the name of the unique DNA recombination experiment that occurred in the laboratory in which one plant cell successfully incorporated a desired gene. That cell is subsequently used to regenerate whole plants and is the “foundation” of a GMO strain. For example, one event name for herbicide-tolerant corn is NK603.

Second, GMOs may also be identified by the unique protein they express. In the case of event NK603, the protein expressed is CP4 EPSPS. Thirdly, the GMO may be identified by the trade name under which it is sold commercially.

Cauliflower Mosaic Virus

GM crops around the world –then and now

Current GMO production mainly comprises four crops: soybeans, maize, cotton, and rapeseed/canola. Global trade of these crops and their main derivatives is dominated by material of GMO origin. In addition, global planting of these four crops includes a very high percentage of biotech seed (78% of soybean, 64% of cottonseed, 33% of maize, and 24% of rapeseed/canola globally; ISAAA 2016). Within these crops, there are several GMO proteins currently important to the grain and seed trade. The cultivation of GM plants is increasing globally, as is the utilization of stacked traits - including two or more novel traits in the same plant. The first field trials of GM plants began in the United States and France in 1986, with herbicide-resistant tobacco. The first country to allow commercialized GM plants was China, which introduced a virus-resistant tobacco in 1992. The first GM crop approved for sale in the US was the FlavrSavr tomato in 1994. In that year, the European Union also approved its first GM plant for sale, which was a herbicide-tolerant tobacco. Commercialized cultivation of GM plants such as corn and cotton began in 1996. In 2016, 11 different types of GM crops were commercially grown on 457 million acres (185 million hectares) in 26 different countries around the world.

Genes that encode proteins (traits) need genetic elements called promotors in order to initiate the expression processes.

A very effective promotor is known as 35S. This promotor is derived from a common plant virus, the cauliflower mosaic virus. It is common practice in DNA-based analysis to detect the 35S promotor instead of the encoding gene as many different genetic modifications use the same promotor. The problem is that unmodified plants can be infected by the actual cauliflower mosaic virus. Such plants would be GMO-positive in a DNA-based analysis without ever having been transgenic. Cauliflower mosaic virus (CaMV) infections are widespread among cruciferous plants, including canola. To be sure, screen for CaMV in the DNA analysis.

The global trade in soybeans, maize, cotton, and rapeseed/canola is dominated by material of GMO origin.

The most commonly approved GMOs are herbicide-tolerant traits. Since 2007, the number of approvals for stacked events has been more than for single events.

The leading cultivators of GM crops

Table 1 shows the global cultivation of GMOs in 2016. Adoption rates of GM crops in the countries where they are planted is often high. USDA survey data from 2016 shows that herbicide-tolerant soybeans comprised 94% of the planted acreage in the United States, herbicide-tolerant cotton comprised 93% of the planted acreage, and herbicide-tolerant corn comprised 92% of the planted acreage. The corn plantings comprised 3% insect-resistant, 13% herbicide-tolerant, and 76% stacked insect-resistant/herbicide-tolerant varieties. The cottonseed plantings comprised 4% insect-resistant, 9% herbicide-tolerant, and 80% stacked insect-

GMO Proteins Important to the Grain

• CP4 EPSPS

The expression of CP4 EPSPS transgenic protein in plants results in glyphosate herbicide tolerance. This protein is expressed in commercial varieties of creeping bentgrass, sugarbeet, rapeseed/canola, soybean, cotton, alfalfa, potato, wheat, and corn.

• Bt-Cry1F

The expression of Bt-Cry1F transgenic protein results in insect resistance. This protein is effective against the larvae of lepidopteran pests such as the tobacco budworm, beet armyworm, soybean looper, cotton bollworm/corn earworm, European corn borer, southwestern corn borer, fall armyworm, and black cutworm. This protein is expressed in commercial varieties of corn and cotton.

• Bt-Cry34Ab1

The expression of Bt-Cry34Ab1 transgenic protein in plants results in insect resistance. This protein is effective against the larvae of coleopteran pests such as the corn rootworm. This protein is expressed in commercial varieties of corn.

• Bt-Cry1Ab, 1Ac, & 1A.105 resistant/herbicide-tolerant varieties. The US also planted biotech soybean (herbicide-tolerant), canola, sugarbeet, alfalfa, and others.

The expression of Bt-Cry1Ab, Cry1Ac, and/or 1A.105 transgenic protein results in insect resistance. The proteins are effective against the larvae of lepidopteran pests such as the European corn borer, tobacco budworm, cotton bollworm/corn earworm, pink bollworm, beet armyworm and soybean looper. These proteins are expressed in commercial varieties of corn, cotton, and tomato.

In Brazil, approximately 96.5% of soybean acreage was biotech. 36.7% of the acreage was herbicide-tolerant, and 59.8% was stacked insect-resistant/herbicide-tolerant. Approximately 88.4% of maize in Brazil is biotech, with the majority containing stacked traits. Approximately 79% of the cottonseed crop there was biotech.

In Canada, approximately 93% of rapeseed/canola acreage is herbicide-tolerant. 94% of the soybean, 92% of the corn, and nearly 100% of the sugar beet is biotech. In India, approximately 96% of cotton planted is modified by the Bt bacterium. In China, biotech cotton comprised 95% of the acreage in 2016. In Paraguay, biotech resistant corn was first commercialized in 2013,