Gene Constructs may be Unstable

The most common application of GM technology is its use to modify plants used to grow food and feed crops.  The consequences of using gene ‘constructs’ to create new types of crop plants may be unpredictable.  A major concern among scientists is that gene ‘constructs’ may be ‘unstable’ and could cause unexpected and undesirable changes to the genetic make-up of the plants they are transferred into.

The ‘Vector’ is used to carry the foreign gene into the plant. A commonly used vector is a bacterium called Agrobacterium tumefaciens because it has the ability to penetrate the cell walls of plants. After the bacterium has fulfilled its purpose as a carrier, it is killed using an antibiotic. However UK government research has shown that the antibiotic does not always kill the bacteria. The bacteria have been found to survive for up to 13 months inside the plant (as well as plants bred from it) and that after six months 12.5% of these bacteria still contained foreign genes which the bacteria could infect the plant with. (R.J. McNicol, G.D. Lyon, Y.M. Chen, C. Barrett og E. Cobb, The Possibility of Agrobacterium as a Vehicle For Gene Escape, (undated) MAFF Research & Development Surveillance Report nr. B95.)

Another common GM gene transfer or transformation procedure is known as ‘biolistics’ and involves the use of an instrument called a ‘gene gun’. In this procedure the foreign gene DNA construct is coated onto tiny particles of gold or tungsten metal. The DNA-coated metal particles are then loaded into a gene gun. The gene gun using high air pressure is then used to fire these DNA-metal particles through the plant cell wall. As in the case of gene transfer via Agrobacterium tumefaciens, in a very small number of the initially treated cells, a proportion of the delivered foreign gene construct will splice itself into the host cell DNA.

The ‘Foreign’ gene is selected because it has certain characteristics scientists want to give to the plant they are modifying. Foreign genes cannot be inserted into the plant’s DNA with any precision.   This is a problem because scientists know that the number of foreign genes that reach the plant’s DNA and where on the DNA chains the foreign genes insert themselves can critically effect the plant’s genetic behaviour. Unfortunately, when foreign genes are transferred into plants there is no control over where they will be located on the DNA chain or how many copies of them will be incorporated into the DNA. The random and uncontrolled distribution of foreign genes into a plant could modify the plant in unpredictable ways.

The ‘Promoter’ genetic on-switch is used to activate the foreign gene once it has been transferred into the plant. Because the foreign gene is alien to the plant (not from that plant species), the regulatory structure of the plant cannot control it - the plant cannot ‘switch on’ or ‘switch off’ the foreign gene to regulate its behaviour.  Scientists therefore have to attach what is called a ‘promoter’ to the foreign gene.  The ‘promoter’ most often used is called 35S, which comes from a plant pathogenic virus known as Cauliflower Mosaic Virus (CaMV). This virus ‘promoter’ does not work as precisely as a plant’s natural regulatory system - in fact it is so powerful that it ‘switches-on’ the foreign gene in every cell of the plant, at all times, and at very high levels. This is completely at odds with natural gene function and the consequences are largely unknown.

The ‘Marker’ gene is attached to the foreign gene to enable scientists to ‘see’ if the foreign gene has been successfully transferred into the plant’s DNA.  The marker gene most commonly used is an antibiotic resistant gene. When the foreign gene and the marker gene have been successfully transferred into the plant’s DNA, the marker gene passes resistance for a certain antibiotic to the plant so that when that antibiotic is applied, the resistant cells survive and the others are killed.  However, marker genes are retained in the plants after they are developed for use as a food crop. This is a source of continuing controversy because it is suspected that the antibiotic gene could enter the human gut and be transferred to gut bacteria causing them to become ‘superbugs’ which would be resistant to antibiotic drugs.  The British Medical Association has stated that “the BMA believes the use of antibiotic-resistant marker genes in GM food stuffs is a completely unacceptable risk, however slight, to human health.” 

(British Medical Association, The Impact of Genetic Modification on Agriculture, Food, & Health An Interium Statement (1999), p. 13.)

The GM Transformation Process Can Be Disruptive

GM technology transfers genes from one organism into another. This insertion of foreign genes into an organism can disrupt the organism’s natural gene function. Disturbance of plant host gene function can occur in a number of different ways. Firstly, the foreign gene can insert itself within host gene regions or their genetic switch-control elements, thereby disrupting their functions. Secondly, the GM-transformation process in general is known to introduce through as yet unknown mechanisms hundreds or even thousands of additional mutational defects in the DNA with potentially devastating consequences on global host gene function.

Summary

GM technology is an imprecise and unpredictable process because (a) the act of inserting foreign genes into plants can ‘scramble´ the plants´ own host genes, thus disrupting the plants´ genetic functions; and (b)  the consequences of using gene ‘constructs’ may create genetic instabilities. GM technology manipulates genes in the absence of a comprehensive understanding about how they behave – scientists do not fully know how genes interact with each other or the chemical environment within or outside an organism.  It can neither be assumed that a gene, which performs a certain function in one organism, will perform the same function when transferred into another organism – nor can it be guaranteed that a gene, which is safe in the original organism will be safe in the organism it is transferred into.