2.5—Promoters can insert naturally into DNA
The transgene promoter “start-signal” used in plant genetic engineering comes from a plant virus that is widely distributed in plants and known to often insert its DNA into plant genomes.
Analysis of Peer-Reviewed Research:
Genetic Roulette suggests that silent plant virus genes buried in plant genomes are a disaster waiting to happen. What this disaster might be is never described and Genetic Roulette provides no scientific citations to give the uninformed reader a clue as to what it might be. This section is a storm in a teacup as the scientific literature shows that no virus genes carried inside plant genomes has ever caused any harm to humans. No plant virus has caused a human disease or infected humans.
The genetic start-signal referred to as the 35S promoter is used in several commercial transgenic crops. It’s a gene start signal from Cauliflower mosaic virus. As the name might suggest, this type of virus infects a wide range of cabbage family crops, including cauliflowers and Brussels sprouts. These viruses belong to a common encountered group of plant viruses that use the nucleus of plant cells as a launching pad to make more virus particles.
Genetic Roulette’s discussion in section 2.5 is a continuation of the preceding section 2.4. A scientific mistake about virus biology in the earlier section is relevant to the claims in section 2.5. Jeffrey Smith has assumed that because these viruses do not need to necessarily insert their DNA into plant genomes in order to multiply, that they’d never do so. Where Smith has got it wrong is to accept incorrect scientific advice. These viruses always replicate using cell nucleus and occasionally insert virus DNA fragments in plant chromosomes, by accident it seems. Thus many food crops including potato, tomato, banana and rice have Cauliflower mosaic virus -like DNA fragments in their genomes.
We have not suffered any harm from eating the existing foods that have Cauliflower mosaic virus-like DNA fragments inserted in them. They have not triggered production of viruses that cause harm to humans, and their demonstrable safety is a realistic indication that these hypothetical hazards are unimportant to humans. We have a history of safe use of such food.
To repeat, this section is a storm in a teacup. The unusual events that Jeffrey Smith postulates are similar to accidents of evolution that have been happening with plants for millions of years. They are rare events involving viruses that do not cause any harm to humans and don’t infect humans. They are even less likely to harm humans because unlike the random nature of evolution, new transgenic varieties with their carefully designed DNA inserts are subject to intense regulatory scrutiny to make sure that hazardous outcomes have not occurred.
1. The speculation by Smith about virus activation by transgene promoters is very general, without any specific example connected with plants.
2. Fragments of DNA from pararetroviruses are widely present in potato, tomato, banana, plantain, rice and other plant genomes. The precursor of the 35S promoter used to drive many first generation transgenes is a DNA segment from Cauliflower mosaic virus, which is pararetrovirus (Hass M and others 2002, Hull and others 2000). Smith does not mention here that numerous DNA inserts derived from various other pararetroviruses have been found widely distributed in chromosomes of different plants, including food crops such as potato, tomato, banana and rice (Gayral, and other 2008, Harper and others 2002, Hansen and others 2005, Staginnus Richert-Pöggeler 2006, Staginnus and others 2007). So much so, that their common occurrence in plant material makes it unreliable to use chemical detection of the 35S promoter as a means of identifying genetically modified crops. This difficulty is because pararetrovirus DNA fragments that can be easily found in non-GM crops can react in a similar fashion in DNA tests used to find out whether crops contain the 35S promoter. The life cycle of pararetroviruses includes an obligatory stage of passing through the nucleus — giving them ample opportunity to insert into chromosomes (Hass M and others 2002). Pararetroviruses are distinct from retroviruses that infect humans and animals because they have DNA inside their viral particle not RNA. They also differ from animal retroviruses in that they don’t have an obligatory insertion of DNA into the cell chromosomes as a step in their life cycle. Genetic Roulette has mistaken this lack of obligatory insertion to mean that chromosomal insertion never occurs when these viruses do occasionally accidentally insert their DNA into chromosomes. Smith doesn’t mention any of these well-established aspects of pararetrovirus biology.
3. The low frequency activation of other plant viruses by transgenic promoters would be similar to rare events that can occur in all plants. Smith discusses the potential hazards of extremely rare events that might happen if other plant viruses were accidently activated by the transgenic DNA containing the 35S promoter. He does not consider the analogous events that might occur from the many known insertions of the other pararetrovirus DNA in non-genetically manipulated plants. A similar hypothetical activation of other plant viruses could also occur during the occasional scrambling of DNA of any plant growing in the field when chromosomes are damaged from radiation and from other processes that continually disrupt chromosome structure. The genetically engineered insertions are subject to regulatory scrutiny but the numerous non-engineered disruption of DNA are completely unregulated. The plant viruses concerned do not infect humans.
Gayral P, and other (2008) A single Banana streak virus integration event in the banana genome as the origin of infectious endogenous pararetrovirus. J Virol. 82(13):6697-710.
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.
Hansen CN, Harper G, Heslop-Harrison JS. (2005) Characterisation of pararetrovirus-like sequences in the genome of potato (Solanum tuberosum). Cytogenet Genome Res. 2005;110(1-4):559-65.
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 35S 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
Staginnus C, Richert-Pöggeler KR (2006) Endogenous pararetroviruses: two-faced travelers in the plant genome. Trends Plant Sci. 11(10):485-91.
Staginnus C, and other (2007) Endogenous pararetroviral sequences in tomato (Solanum lycopersicum) and related species. BMC Plant Biol. 7:24.
Tribe D (2008). Blog posting. Gene-chips prove transgenes are clean genes. gmopundit.blogspot.com/2008/07/gene-chips-prove-transgenes-are-clean.html
1. When certain viruses infect organisms, they splice themselves into the host’s DNA.
2. These embedded viral sequences can be passed on to future generations and even be inherited by future species.
3. Most ancient embedded viral sequences become mutated over time, but some may be intact, just not switched on.
4. If the GM promoter is inserted in the vicinity of the dormant virus, it might switch on, resulting in virus production and a potential catastrophe.
Genetic Roulette mentions in this section that virtually all organisms have silent virus genes embedded in their chromosomes. Smith imagines that the promoter “start-signal” used to drive expression of some genetically engineered traits has a very low probability of activating silent viruses. This he claims could “produce potentially dangerous viruses”.