briefly describe three ways in which an organism may be genetically modified to produce a GMO.
Submitted by: bioman1o1
Expert response from Allan Wenck
Head of US Trait Validation Operations, Bayer
Monday, 12/06/2017 19:20
Thanks for the question, which I will address in two ways here.
1. What are three ways that organisms are modified by scientists? Here I will focus only on plants.
a. Agrobacterium: Agrobacterium tumefaciens (Agro) is a naturally occurring soil organism that causes a disease in plants called crown gall disease. In the late 1970s, Mary-Dell Chilton discovered that Agro actually transfers genes (DNA) from the Agro to the plant cell, where it becomes integrated into the plant DNA and is treated just like any other plant DNA. The genes transferred cause the plant to produce a gall (growth) and to produce certain compounds, which the Agro eats. However, other scientists discovered ways to modify Agro such that it still transfers new genes to plants, but the detrimental genes that cause the gall and cause the plant cell to produce these compounds are deleted and replaced by beneficial trait genes –as described below. Once the DNA is delivered to the plant cell, that cell (through various means) can be induced to grow and develop into a whole plant containing the new traits.
b. Biolistic transformation: Certain plant cells are resistant to Agro transformation. However, scientists have developed physical methods to “fire” gold “particles” into plant cells in culture or in tissues. These “bullets” are very tiny and are coated with beneficial trait genes. Some of these “bullets” will hit a plant cell. Once there, the trait genes can dissolve off of the gold bullets and become integrated into the plant DNA, where it is treated like any other plant DNA. As above, once the DNA is delivered to the plant cell, that cell (through various means) can be induced to grow and develop into a whole plant containing the new traits.
c. Protoplast transformation: In some cases, scientist are able to strip away the cell walls of plant tissues using specific enzymes and release them as individual cells (protoplasts) that can be cultured and further developed into individual plants. In this process, there are several ways that scientists can introduce trait genes into these isolated cells. These trait genes become integrated into the plant DNA where it is treated like any other plant DNA. As above, once the DNA is delivered to the plant cell, that cell (through various means) can be induced to grow and develop into a whole plant containing the new traits.
2. Here, I will address specific types of modifications that are present in current GMO plants on the market – how the plants are modified such that they have new traits.
a. Insect resistant proteins: Plants can be modified to express new proteins that are toxic to specific insects but are not toxic to other organisms. One of the first genetically modified plants on the market was of this type. Scientists introduced a gene from bacteria called Bacillus thuringiensis (BT) into plant cells where it expresses the BT protein. BT has been used for many years as a bacterial spray on plants by both conventional and organic farmers to control caterpillars. However, the whole BT is not needed. Only a specific set of proteins are responsible for caterpillar control. Scientists isolated the trait genes coding for these proteins and expressed them in plant cells. Now the plant cells control caterpillars without the need for spraying. The protein is very specific for certain caterpillars because of specific conditions in the stomach of caterpillars that is different than people and specific receptors on the gut cells in caterpillars that are not found in people.
b. Herbicide resistant proteins: Probably the best known traits are herbicide resistant traits. Farmers need to control weeds in fields. Traditionally, they were sprayed by very specific herbicides that only were (somewhat) effective against one set of weeds, but not other plants that the farmer was growing. Alternatively, farmers would go through their fields with a cultivator to physically pull up weeds. Two versions of these types of genetically enhanced plants are commonly found.
i. Resistant proteins: Herbicides target specific enzymes/functions within plant cells. For example, glyphosate (the active ingredient in Roundup™) inhibits a specific plant enzyme that makes specific amino acids – animals cannot make these amino acids and we need to get them from things we eat. Scientists found a version of the target enzyme that does not bind glyphosate and keeps working even when glyphosate is present. They were able to introduce this trait into plant cells and were able to develop plant cells that were resistant to glyphosate.
ii. Metabolizing proteins: Glufosinate (the active ingredient in Liberty™) targets a specific enzyme in plants that incorporates nitrogen into the amino acid pathway in plants – not found in animals. Scientists found an enzyme that doesn’t change the target in the plant, but that instead breaks down the glufosinate in the plant cell – rendering it inactive. They were able to introduce this enzyme/trait into plant cells and generate plants resistant to glufosinate.
c. Virus resistance: Virus resistance based on GM traits is the only reason that Papaya is a viable crop in places like Hawaii. A specific virus decimated papaya groves throughout the Hawaiian Islands. This virus enters plant cells where it releases its genetic material. The virus essentially “takes over” the plant cell to produce more virus which is then released to keep the disease process going throughout the plant and where it is available for spread to other plants by insects. Scientists found that if a plant cell expresses the coat protein, which covers the virus’s’ genetic material, then that material is never released to do its “work” in the cell. The plant cell is resistant to the virus and thrives even when exposed to the virus. This technology is also available in a small number of squash varieties. It has been demonstrated to work in other plants – such as tomato, cucumber and melon – but is not available on the market due to production costs in bringing the trait to market.