In nature, the question of whether any given example of horizontal gene transfer is beneficial or harmful is answered over long periods of co-evolution and natural selection. It cannot be answered based on the limited knowledge of the genetic engineer or under the limited timescales in which GMO introduction takes place. Neither can it be answered by the inadequate “safety assessment” regimes that are currently used in GMO regulatory processes around the world.
Use of potent plant promoters in GM gene cassettes attempts to override host plant gene regulatory mechanism
The random insertion of the GM gene cassette at the vast majority of locations within the plant cell DNA results in little or no expression of the transgene. This “silencing” of the GM gene cassette, including any associated antibiotic selectable marker gene present, is in part due to the plant’s natural response to invasion by foreign DNA, as occurs, for example, in the case of infection by viruses. This silencing occurs despite that fact that in most cases plant genetic engineers use the powerful 35S cauliflower mosaic virus (CaMV) promoter or similar powerful promoters in an effort to overcome GM gene inactivation.
Consequently the selection procedure of plants via the GM transformation process actively selects for purely fortuitous events in which the GM gene cassette, plus any associated antibiotic marker gene, has inserted into those rare sites within the plant’s DNA that allow it to function. These rare sites are by definition regions within the plant cell DNA where active host genes and their control elements are located. In other words, the GM plants contain GM gene cassette insertions into regions of the DNA where their own genes are active (gene regions represent only a tiny fraction of the total genome). This fact maximizes the chances that the plants’ host gene function will be disturbed – with unexpected downstream consequences to their biochemistry and performance.
In addition, the use of potent plant promoters such as the CaMV to switch on GM genes has other potential downsides. The CaMV promoter functions in all the different types of cells within the plant. Such ubiquitous expression is necessary in cases such as when the GM crop is engineered to tolerate being sprayed with a herbicide, to ensure that the plant survives.
But in other situations, ubiquitous GM gene expression is not so desirable. For example, GM maize engineered with the insecticidal Bt toxin gene obtained from bacteria aims to target either the corn borer or rootworm pest. Therefore the GM Bt toxin gene only needs to be expressed in stems, corn cobs, and roots, in order to ensure protection from these pests. However, the use of the CaMV promoter to drive expression of the Bt toxin transgene unit (as is the case in all current GM crops) results in the presence of this insecticide in all plant structures, not just the stems, cobs, and roots. This in turn increases the possibility of toxic effects on non-target insect populations that may feed on the pollen of these Bt GM crops, such as bees and butterflies. Thus valuable pest predator or pollinator insect populations may be harmed when feeding on Bt GM crops.
In conclusion, the use of ubiquitous promoters such as the CaMV in an effort to override the host plant’s gene regulation systems and force expression of the GM gene at high levels may have undesirable effects on plant biochemistry, crop performance and the surrounding environment.
In contrast, in natural breeding and even in mutation breeding (mutagenesis), which exposes plants to radiation or chemicals to induce genetic mutations (inheritable changes), the plants’ own gene regulation systems remain active.
In other words, scientists use genetic engineering to bypass the plants’ natural gene regulation systems and to re-programme their genetic functioning. Natural breeding, on the other hand, uses the inherent genetic potential in plants and does not deliberately disrupt their gene regulation system.
Muddying the waters with imprecise terms
GMO proponents often use the terminology relating to genetic modification incorrectly, blurring the line between genetic modification and conventional breeding.
For example, they claim that conventional plant breeders have been “genetically modifying” crops for centuries by selective breeding and that GM crops are no different. But this is incorrect. The term “genetic modification” is recognised in common usage and in national and international laws as referring to the use of laboratory techniques, mainly recombinant DNA technology, to transfer genetic material between organisms or modify the genome in ways that would not take place naturally, bringing about alterations in the genetic makeup and properties of the organism.
The term “genetic modification” is sometimes wrongly used to describe marker-assisted selection (MAS). MAS is a relatively uncontroversial branch of biotechnology that can speed up conventional breeding by identifying natural genes that confer important traits. MAS does not involve the risks and uncertainties of genetic modification. It is supported by organic and sustainable agriculture groups worldwide, with objections mostly focusing on patenting issues.
Similarly, “genetic modification” is sometimes wrongly used to describe tissue culture, a method that is used to select desirable traits or to reproduce whole plants from plant cells in the laboratory. In fact, while genetic modification of plants as carried out today is dependent on the use of tissue culture, tissue culture is not dependent on GM. Tissue culture can be used for many other purposes, including some safe and useful ones.
Using the term “biotechnology” to mean genetic modification is inaccurate. Biotechnology is an umbrella term that includes a variety of processes through which humanity harnesses biological functions for useful purposes. For instance, fermentation in wine-making and breadmaking, composting, the production of silage, marker-assisted selection (MAS), tissue culture, and even agriculture itself, are all biotechnologies. GM is one among many biotechnologies.
GM proponents’ misleading use of language may be due to unfamiliarity with the field, or may represent deliberate attempts to blur the line between controversial and uncontroversial technologies in order to win public acceptance of GM.
Contained and uncontained use of GM technology
GM technology is used in both contained and uncontained systems. “Contained use” means that the use of GM technology does not result in the deliberate release into the environment of a living GMO that is capable of reproducing and spreading.
In Europe, all laboratory and industrial uses of GM technology are regulated by the Contained Use Directive.10 Containment can be physical, in the form of barriers preventing escape, chemical, or biological (by genetically crippling the GMO so that it cannot reproduce).
Contained medical uses of GM technology include diagnosis of disease and manufacture of pharmaceuticals and GM viruses used to deliver somatic (non-germline and thus non-inheritable) gene therapy. Contained uses of GM technology in plant breeding are confined to the laboratory and include identification of genes of interest and study of their functions and protein products under normal and disease conditions.
We oppose non-contained uses of GM technology but support contained use, as long as containment is effective. There is always risk of escape during contained use, either due to physical or biological “leakiness”. However, for most current and envisioned applications, the benefits outweigh the risks when strong and well-designed containment strategies are employed.
Genetic engineering is different from natural/conventional plant breeding and poses special risks, as is recognized in national and international biosafety laws. The genetic engineering and associated tissue culture processes are highly mutagenic, leading to unpredictable changes in the DNA and proteins of the resulting GM crop that can lead to unexpected toxic, allergenic and nutritional effects."
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