Gene technology: what is it and how is it used?
GroundCover™ Issue: 41
MODERN CROP breeding uses biotechnology to produce new varieties with improved yield, product quality and sustainability.
Gene technology is one aspect of biotechnology. It involves the introduction of new or altered genes into plants in the laboratory. The outcome is commonly called a genetically modified organism (GMO).
What is gene technology?
DNA is DNA is DNA and makes protein. Genes are made of DNA, a large molecule found in every cell of every living organism. Every gene is made of the same four units, the only difference between genes being the order of the four units of the genetic code.
DNA is a part of food and the average person consumes 2 x 1016sup> genes, that's 20 million billion genes eaten every day. As a food, these genes are the same regardless of whether they come from a plant, animal or microbe. The genetic information is not taken up by the consumer. You may eat pork but you won't grow a tail.
And when an animal eats a GM pasture plant, all of the genes in the plant are broken down to their basic chemical parts in the digestive process.
When a gene is activated, or 'turned on', it directs the synthesis of a specific protein according to its code, the order of the four units. The protein products of genes have different functions and may have different food properties. A few may even be difficult to digest or cause allergic-type reactions.
Basic gene knowledge
The primary contribution of gene technology to date has been in scientific investigations in which a great deal of new know ledge has been gained about how plants grow and develop. In the course of these studies, genes with potential for application in breeding have been isolated and their beneficial properties have been demonstrated in the lab and glasshouse.
How is gene technology used?
Here are four examples of applied gene technology which illustrate the current range of uses.
Transfer from a related species: disease resistance
Gene technology is used to transfer a beneficial gene from a related species into a crop plant in a direct and efficient way. For example, the rust diseases are serious problems for wheat growers in Australia. Conventional breeding controls these diseases by transferring resistance genes from other species into wheat, but the process is imprecise and cumbersome.
A source of resistance genes is rye. Until now, transfer of resistance genes involves a cross between wheat and rye, followed by several generations of back -crosses of the hybrid with wheat to eliminate as much of the rye genetic material as possible while retaining the resistance genes. In practice, many rye genes end up in the new wheat variety, some with undesirable characteristics. For example, the gene that makes sticky dough is located close to the disease-resistance genes on the rye chromosome segment.
A major research effort at CSIRO Plant Industry over a 15-year period resulted in a world-first isolation of resistance genes for rust diseases.
Now that we know what resistance genes look like, we can transfer them with preci sion from wild relatives to wheat and barley.
Transfer from an unrelated species: insect resistance
Gene technology is also used to introduce a gene from an unrelated species or to introduce a gene constructed in the laboratory. Genetically modified cotton is a working example.
Insect damage is the major problem facing cotton growers and large amounts of insecticides are applied during the growing season to control pests. The insecticides are an imprecise solution, lacking specificity and killing both pests and beneficial insects. Insecticides have a host of other detrimental environmental effects which attract community opposition, the dispute over endosulfan with neighbouring cattle growers being a prime example.
Organic farmers use a natural insecticide, called Dipel, to combat caterpillars. Dipel contains a protein produced in the spores of the bacterium, Bacillus thuringiensis (Bt), that is toxic to caterpillars but nothing else. Scientists have isolated the bacterial gene coding for the toxic protein, modified it in the laboratory to work effectively in plant cells and then transferred it to cotton.
The first Bt gene in Australian cotton is owned by Monsanto and is marketed with the name Ingard®. Although Ingard does not provide complete insect control, it has reduced insecticide applications by half.
In this example, gene technology results in the production of a protein inside the cells of the cotton leaf that would not otherwise be found there.
But this insecticidal protein is commonly applied to the outside of leaves, especially in organic farming operations.
Turning off gene and protein: modifying quality characteristics
In its alternative guise, gene technology is used to turn off the function of a plant gene, resulting in no new protein, rather the absence of one normally present.
An artificial gene is made in the laboratory by reversing part of the code of the gene we wish to turn off. This new gene makes no product itself but triggers a mechanism called gene silencing which prevents the targeted plant from making its specific protein.
Until now, conventional plant breeding has exploited rare mutations to remove unwanted genes. We wouldn't have canola without this technique. The breeding of canola relied on the identification of a naturally occurring mutation that prevented the synthesis of unwanted oils in the seed of the rape plant.
The use of chemical mutagens can speed up the process, but the process is still imprecise and other deleterious mutations are likely to arise at the same time.
Gene-silencing technologies, pioneered at CSIRO Plant Industry, are being used in many laboratories worldwide to modify the oil composition of oilseed crops, especially canola. Oil synthesis in the seed is a multi-step process, each step catalysed by a protein enzyme encoded by a specific gene.
Removing the activity of one of these enzymes, delta-12 desaturase, prevents the conversion of oleic to linoleic acid. The resulting high oleic oil is a high value oil because of its stability at high temperatures, making it a superior cooking oil.
On the other hand, increasing stearic acid by removing a different enzyme, delta-9 desaturase, results in more solid oils/fats used in margarine.
Gene silencing could open up new markets for canolas with high value oils.
'Immunisation': controlling virus diseases
The final example illustrates how gene technology can provide an 'immunisation' effect to control virus diseases of plants.
Potato leaf roll virus is a serious problem, limiting yield and damaging the product. Because the virus is spread by aphids, it is controlled by insecticide sprays. Knowing when and how much to spray is always difficult.
CSIRO scientists have synthesised a gene containing a small part of the virus and have shown that this' gene is effective in preventing virus disease. The technology works so well that transgenic potato plants are said to be immune because they exhibit no symptoms of disease and at the same time virus replication is prevented, which blocks the spread of the disease.
Just as in the previous example, the technology is used to turn off function. The synthetic gene produces a small strand of RNA but does not produce any viral protein.
Field trials at multiple sites have proven its performance under normal farming conditions. The potato plants are indistingui shable from non-transgenic potatoes, except when they are challenged with virus and the non-transgenic plants show disease symptoms.
How does gene technology move from lab to farm?
From the initial discovery of a new gene, there is a great deal of experimentation and testing in the lab and the glasshouse, followed by repeated small- and larger-scale testing in the field. All steps are closely regulated and the resulting data examined at each step.
Once the performance of a new gene has been demonstrated in the field, it then enters a breeding program to introduce it into elite varieties. Product testing and final regulatory approvals are necessary before it is released as a commercial crop variety to be sold to the farmer.
Once in the field sustainability issues such as weed or pest resistance will still be there. An appropriate management system is important for growers to gain maximum benefit from gene technology.
Five common uses of gene technology
- Basic knowledge
- Gene transfer from a related species: USED FOR disease resistance
- Gene transfer from an unrelated species: USED FOR insect resistance
- Turning off gene and protein: