5.6—The 35S promoter has been thoroughly researched
Artificial laboratory experiments with the 35S plant virus promoter are not a good guide to what is possible or likely in environments outside that the laboratory Petri dish
Analysis of Peer-Reviewed Research:
This section of Genetic Roulette builds on a platform of misinterpretations and scientific errors made in earlier sections of the book. These errors pertain to the properties and biological behavior of a plant virus derived “start-signal” that is used to drive transgene activity in genetically engineered plants.
In our section 2.5 we explain how 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. In item 2 of that page we document the numerous scientific reports showing that fragments of DNA from this group of viruses are randomly present in potato, tomato, banana, plantain, rice and other plant genomes. In our section 2.4 we explain why the promoter “start-switch” does not accidentally switch on harmful genes, and in section 2.6 we show that transgenic plants containing the 35S virus promoter start signal are not genetically unstable. Additionally, in section 5.4 we explain how transfer of complete transgenes to bacteria from transgenic plants doesn’t occur. These sections address many of the misunderstandings and misleading statements on which section 5.6 of Genetic Roulette is based.
This currently considered 5.6 section of Genetic Roulette is mainly directed at the possible effects of transfer of the 35S DNA to bacteria or to human cells from transgenic plants. It fails to explain why transfer of the same kinds of DNA, already widely present in conventional plants, and present in virus infected plants such as cabbages, does not pose similar risks, improbable as they are. No harm to humans has been shown to result from this source of exposure to the same kinds of DNA that Genetic Roulette worries about. Genetic Roulette also fails to explain why the minute fraction of DNA in our food that is transgenic DNA is a hazard, while the great bulk of DNA containing many analogous promoter DNAs causes no apparent harm.
Excellent rebuttals of Smith’s opinions in this section are provided in the scientific literature, but Smith simply avoids informing the reader about these articles. In science, failure to cite relevant references is misconduct, and omission of direct rebuttals of a scientific hypothesis is serious misconduct indeed. As Smith is not a professional scientist, his failure is merely negligence, but in Genetic Roulette we find serial negligence. In his section 5.6 Smith repeats a confused version of an earlier figment of his imagination (see our section 5.4) concerning a report by Trudy Netherwood (Netherwood and others 2004) on digestion of food DNA in the human gut. Contrary to Smith’s opinion, Trudy Netherwood did not detect a full transgene in gut bacteria, and explicitly said so. Smith clearly doesn’t know the difference between a fragment of DNA and a gene, but his repeated use of fabricated evidence raises serious issues.
1. Negligence with evidence and avoidance of rebuttals cited in earlier sections of Genetic Roulette provide a platform for fanciful speculation. This section starts by repeating earlier misinformation invented by Smith that we have already evaluated in detail in sections 2.4, 2.5, and 2.6. To re-iterate the main points given there: transgene promoters do not activate nearby genes; numerous inserts of various pararetroviruses posing the same hypothetical risks as Smith attributes to the 35S promoter are found in conventionally bred plant genomes, such as genomes of rice, banana, potato, and tomato; pararetroviruses containing similar promoter DNA to the 35S promoter are common in our food; during infection of plants with viruses, pararetrovirus DNA passes through the plant nucleus in uncoated form which can insert itself into plant genomes (Hardwick and others 1994, Hass and others (2002) Hull and others 2000), and transgenic DNA in genetically engineered plants containing the 35S promoter is not genetically unstable (Hull and others 2000). Plant genes contain promoters that are closely similar to human gene promoters (R. Hull, unpublished observations).
2. Large amounts of the DNA of the 35S promoter are present in existing non-GM foods and similar promoters exist as DNA inserted into the genomes of conventionally bred food crops. Smith devotes a lot of effort to discount these facts but he is wrong. Transgenic foods are not the only source of 35S promoter, since the virus commonly infects common cabbage-family food plants (Hardwick and others 1994). His argument that 35S promoter DNA would be less accessible to gut bacteria or human cells in virus infected plant cells than when it integrated in the plant DNA is simply not based on any rational facts. The natural life cycle of pararetroviruses passes through the nucleus (Hass and others 2002) and Smith is wrong to imply that it doesn’t. Similar plant pararetrovirus DNA is even found inserted into chromosomes of several conventionally bred plant species (Gayral and others 2008, Harper and others 2002, Hansen and others 2005, Staginnus and Richert-Pöggeler 2006, Staginnus and others 2007), which is further evidence that naked pararetrovirus DNA passage through plant nuclei right next to plant chromosomes. All this DNA we eat regularly.
3. Artificial laboratory experiments do not give a good indication of what is likely in nature. The 35S promoter “start-signal” derived from Cauliflower mosaic pararetrovirus commonly used to activate transgenes can indeed function at a low but detectable level in mammalian cells. The experimental conditions, showing this have been, however, highly artificial. A reporter gene was linked to the 35S promoter and the DNA construction was forced into cultured mammalian cells. This is quite different than the S35 promoter used in a transgenic plant.
4. Accidental assembly of genes being effectively driven by the 35S promoter is an unlikely event. The possibility of intact promoter getting spontaneously transferred from food to human cells, being placed in front of a human gene, and causing the activation of the gene, are, however, a completely different and highly unlikely process. We are exposed to a lot of this potential hazard in conventional diets and we are probably well designed by evolution to deal with it. The cells lining our gut are regularly shed into our feces and continually replaced by new cells. They are the first line of defense against foreign DNA entering out body. The events by which the 35S promoter was used to give low level gene-expression in mammalian cells genes in the laboratory required deliberate genetic engineering. Such events occur very very infrequently by accident.
5. Smith fabricates evidence about the 35S promoter driving expression of herbicide tolerant genes in bacteria. To buttress his assertions about the transgenic 35S promoter being active in making proteins in other organisms, Jeffrey Smith makes reference to a study by Trudy Netherwood and colleagues published in 2004 (Netherwood and others 2004). In fact Trudy Netherwood’s paper specifically refutes this assertion, and presents evidence that the main part of the gene is missing from gut bacteria, making it impossible for the herbicide tolerance trait to be expressed, as we have already mentioned in our discussion of section 5.4, where Smith imagines a similar falsehood. In explicitly repeating this fabrication, Smith says “Furthermore, the bacteria survived in the presence of glyphosate, suggesting that the promoter had activated the herbicide-tolerant transgene” but there is no mention in the Netherwood report about gut bacterial survival in the presence of glyphosate.
6. Scientific expert opinion and facts are omitted from the discussion. While mentioning that there are contrary opinions about the 35S promoter, Smith does not give a citation to them. Authoritative expert opinion in the possible hazards of 35S CaMV promoter specifically addressing the issues raised by Smith was provided by Roger Hull and colleagues of the John Innes Institute in Norwich in 2000. While mentioning several other reports, Smith simply skips over Roger Hull’s response (Hull and others 2000).
Gayral P, Noa-Carrazana JC, Lescot M, Lheureux F, Lockhart BE, Matsumoto T, Piffanelli P and Iskra-Caruana ML(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.
Hardwick NV, Davies JML and Wright DM (1994). The incidence of three virus diseases of winter oilseed rape in England and Wales in the 1991/02 and 1992/93 growing season. Plant Pathol. 43:1045–49. Cauliflower mosaic virus is as common as cabbage.
Harper G, Hull R, Lockhart B and Olszewski N (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, Bureau M, Geldreich A, Yot P and Keller M (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
Netherwood T, Martín-Orúe SM, O’Donnell AG, Gockling S, Graham J, Mathers JC and Gilbert HJ (2004). Assessing the survival of transgenic plant DNA in the human gastrointestinal tract. Nature Biotechnology 22(2):204-209. Transgene DNA is digested to small fragments in the human gut. Some fragments can be detected apparently associated with gut bacteria. Intact full length genes were not detected. No transgene fragments can be detected in faeces.
Staginnus C and Richert-Pöggeler KR (2006) Endogenous pararetroviruses: two-faced travelers in the plant genome. Trends Plant Sci. 11(10):485-91.
Staginnus C, Gregor W, Mette MF, Teo CH, Borroto-Fernández EG, Machado ML, Matzke M and Schwarzacher T(2007) Endogenous pararetroviral sequences in tomato (Solanum lycopersicum) and related species. BMC Plant Biol. 7:24.
1. Contrary to prior assumptions, the CaMV promoter functions in human, animal, and bacteria DNA
2. This promoter transfers into the DNA of human gut bacteria and might also transfer into human DNA
3. Once transferred, it may switch on genes that produce toxins, allergens, or carcinogens, create genetic instability and, in higher organisms, switch on dormant viruses.
Genetic Roulette speculates that if the plant virus derived 35S promoter used in transgenic crops is transferred to bacteria or human cells lining the gut, it will become active in expressing other genes.