2.4—Promoters are precise tools


The promoter, which is the switch that is inserted to turn on specific genes, cannot “accidentally” switch on harmful genes.

See Genetic Roulette’s False Claims at Bottom of Page

Analysis of Peer-Reviewed Research:

This claim of Smith’s is completely unsubstantiated as he uses an example from human gene therapy that has not been scientifically proven. Human gene therapy is far removed from plant engineering and irrelevant to food safety.  This is an example of Smith creating a Straw Man argument. Gene therapy is a deliberately intrusive medical intervention that is used to try and save lives threatened by fatal diseases such as cancer. Genetic manipulation of plants does not involve disruptive injection of genes into humans. Genetically manipulated plants are perfectly normal and genetically disrupted plants would be useless to farmers. It’s impossible for genes inserted into plants to intrude into the human body; as in the digestive canal, food is digested to a harmless soup before being taken up by the body as simple nutrients with no entry of working genes being possible.

Crops containing promoters have been used in agriculture for years and have yielded many positive outcomes such as reduced synthetic pesticides usage, reduced pollution, and lower levels of natural toxins that might cause harm.  On the other hand, many crops that have evolved naturally have produced lethal diseases and toxic substances. In fact, by inserting promoters, there is a higher level of control over what the plant produces than is possible by conventional breeding and ultimately this means it is safer for human consumption.  Agriculture has used selective breeding technologies for thousands of years; GM technologies are simply a very refined tool used that minimizes unwanted mutations.

1. DNA sequences inserted into plants contain promoter components that ensure that only the inserted genes will be expressed. Each genetically engineered gene is deliberately devised with a safety signal that prevents nearby genes being accidentally turned on. Smith is concerned about the first generation promoters being active nearly all the time and thinks this will accidentally turn-on nearby genes. He doesn’t reassure readers that every inserted transgene also has a permanent turn-off switch designed into the DNA. This “turn-off “signal device makes sure that after the promoter “on-switch” has finished allowing the desirable gene to do its job, unintended genes cannot accidentally be turned on.

Genetic Roulette asserts that the first-generation promoters are turned on most of the time. It doesn’t mention that more modern promoter “on-switches”  are used which are much more selective, allowing even better assurance that unintended genes will not be accidentally turned on. Many of these new and different promoters are in use today (Lemaux 2008, Section 3.12.). For example, in a canola (Brassica napus and Brassica campestris) that is engineered to have a different oil composition, a native Brassica plant storage protein promoter has been used (Radke and others 1988) giving more precise control of the activity of transgenes by limiting their activity to seeds that produce oil.

2. There is no evidence to support the wild speculations advanced in Genetic Roulette about accidental activation of harmful genes. The promoter referred to by Smith as the 35S does not activate genes nearby the site of its insertion (El Ouakfaoui and Miki 2005).  The fact that Smith has refrained from alerting the reader to key studies in this area should, in fact, alert the reader to his scientific dishonesty. Smith’s hypothetical argument describes a scenario of plant transgene promoters turning on genes that encode toxins or carcinogens, that has never been reported to happen. In fact it is extremely unlikely to ever happen at all. Most importantly, if genes are expressed that have an adverse affect on the plant, or that change the composition, that would be detected in safety analysis of genetically engineered crops. Safety assessment is rigorously applied to all genetically engineered crops grown for animal feed or for food. There are at least 250 scientific papers published that investigate safety of genetically modified food and document its safety (Tribe 2009).

3. There is no difference between the 35S promoter being inserted in DNA and it being delivered by common plant viruses found in the fields. In nature, virus genes are often found inserted in plant DNA. For example, plant virus DNA has been found in bananas and plantains, tomatoes, potatoes, rice, grapevine, and tobacco (Bejarano and others 1996; Harper and others 2002; Mette and others 2002; Staginnus , Richert-Pöggeler 2006; Tanne, Sela 2005).  The 35S promoter originated from the Cauliflower mosaic virus. Similar virus DNA is found in genomes of many plants that have never been in a genetic engineering laboratory. Given the abundance of plant viruses carrying promoters like the 35S promoter and their presence as DNA inserts in chromosomes, it is just as likely to imagine that common plant viruses could indeed cause all the potential ill effects Smith describes for the 35S promoter.  In dismissing this possibility, Smith makes a scientific mistake.  He claims that viruses related to Cauliflower mosaic virus do not pass through the plant cell nucleus when they multiply inside plants. However, passage through the nucleus is an essential part of their life-cycle. This gives them ample natural opportunities for accidental insertion into the plant chromosomes and where they are often found as DNA inserts (Hass and others 2002). In summary, Smith’s described “accidents” happen in nature. Ironically, it is with GM technology that these “accidents” can be controlled.

4.  Whether inserted by natural evolution or through GM technology, virus DNA in plant genomes doesn’t cause problems. The biosafety implications of the existing virus DNA inserts in plant chromosomes have been discussed in a scientific review by Glyn Harper and colleagues in 2002 (Harper and others 2002).  They show that there are no problems associated with virus fragments inserted into chromosomes.

See also:

2.3 Gene Expression

5.9 Viral Genes and Gut Transfer

6.5 Disease Resistant Crops are Safe for Humans

Resources:

Bejarano ER and others (1996). Integration of multiple repeats of geminiviral DNA into the nuclear genome of tobacco during evolution. Proc. Natl. Acad. Sci. U.S.A. 93:759– 764. www.pnas.org/content/93/2/759 this event mimics artificial transgenic incorporation into plant genome. There are multiple copies of virus DNA in tobacco. Their similarity to the viral DNA is compelling. Tobacco plants are easily regenerated from tissue fragments and this may explain the incorporation of the virus DNA into the germline. Tobacco also has a bacterial DNA inserted into its genome from Agrobacterium.

El Ouakfaoui S, Miki B.(2005) The stability of the Arabidopsis transcriptome in transgenic plants expressing the marker genes nptII and uidA. Plant J. 2005 Mar;41(6):791-800. Strong promoters in the transgenes did not affect the other plant genes in this comprehensive survey of gene activity.

Harper G and others (2002). Review. Viral sequences integrated into plant genomes. Annual Review of Phytopathology 40:119–36. Numerous bits of viruses are found inside the chromosomes of plants that we eat.

Hass M and others (2002) Review: Cauliflower mosaic virus: still in the news. Molecular Plant Pathology. 3(6): 419–429. Description of the virus from which the S35 promoter used in the first generation of GM plants was obtained.

Hull R, Covey S & Dale P (2000). Genetically modified plants and the 35S promoter: assessing the risks and enhancing the debate. Microbial Ecology in Health and Disease 12, 1–5

Lemaux P (2008). Section 3.12. Do viral sequences used in plant genetic engineering create a human health risk? In Review: Genetically engineered plants and foods: a scientist’s analysis of the issues (Part I). Annual Review Plant Biology 59:771–812.

Mette MF and others (2002). Endogenous viral sequences and their potential contribution to heritable virus resistance in plants. The EMBO Journal 21(3):461-469.

Radke SE, and others. (1988). Transformation of Brassica napus L. using Agrobacterium tumefaciens: developmentally regulated expression of a reintroduced napin gene. Theor. Appl. Genet. 75:685–94

Staginnus C, Richert-Pöggeler KR (2006) Endogenous pararetroviruses: two-faced travelers in the plant genome. Trends Plant Sci. 11(10):485-91. Describes the virus sequences that are found in plant genomes. We eat these almost every day.

Tanne E, Sela I (2005). Occurrence of a DNA sequence of a non-retro RNA virus in a host plant genome and its expression: evidence for recombination between viral and host RNAs. Virology.332(2):614-22.

Tribe D (2008). Blog posting. Gene-chips prove transgenes are clean genes. gmopundit.blogspot.com/2008/07/gene-chips-prove-transgenes-are-clean.html accessed Dec 11 2008.

Tribe D (2009). Blog posting. 250+ published safety assessments on GM foods and feeds. gmopundit.blogspot.com/2007/06/150-published-safety-assessments-on-gm.html accessed Jan 29 2009

Genetic Roulette Falsely Claims:

The promoter may accidentally switch on harmful genes

1. Promoters are switches that turn on genes.

2. The promoter used in nearly all GM crops is designed to permanently turn on the foreign genes at the high output.

3. Although scientists have claimed that the promoter would only turn on the foreign gene, it can accidentally turned on the other plant genes — permanently.

4. These genes may overproduce an allergen, toxin, carcinogen or anti-nutrient, all regulators that block other genes.

Smith discusses the possibility that the promoter [see below for definition] may accidentally switch on harmful genes, permanently producing allergens, toxins, carcinogens or plant chemicals that might interfere with uptake of nutrients.

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