Become a fan of h2g2
Genetic modification of plants, along with the issue of human cloning, has been the most passionately-debated scientific topic of recent times. The practice, however, has been around since the 1800s when Gregor Mendel studied the genetic properties of pea plants. Genetically modified (GM) plants have a bad image, even though the vast majority of people do not know what they are and how they are made. This entry aims to deal with this problem. A genetically modified plant has had its genome altered by modern genetic manipulation techniques in some way to produce an organism with beneficial or desirable traits. This does not include traditional breeding methods that have produced the myriad of foods humans enjoy today. GM plants can have their existing genetic make up altered (eg, by having existing genes down- or up-regulated) or having non-native genes ('transgenes') inserted into it. The latter are known as 'transgenic' plants.
Choose a Plant
Firstly one has to choose a plant that you want to modify. The reasons for tinkering with the genetics of a plant are numerous. If you are an academic researcher you will probably choose a plant that is eaten by a huge number of people, such as rice or soy, so that any genetic engineering performed would be beneficial to society as a whole. If you are a multinational corporation you will choose a plant that will make the most money in the long run, such as wheat or barley. GM crops made so far include cotton, soy, rice, maize and oil seed rape.
Choose a Gene
Next, you will need to find a gene somewhere that will impart new, improved or beneficial properties into your chosen plant. So far, the main GM plants have contained either a gene for glyphosphate resistance (a pesticide more commonly known as 'Roundup') or 'Bt'. Bt stands for Bacillus thuringiensis, a naturally-occurring, soil-borne bacteria that synthesises insect-killing toxins. It's harmless to people but very harmful indeed to the pests that attack crops. It is a built-in insecticide! Bt technology has been used in a variety of plants, from cotton to corn.
Genes, or groups of genes, that increase yield (allowing more people to be fed per acre crop grown), lessen environmental impact of intensive agriculture (as mentioned before, such as built-in pesticides) are highly desirable traits to have in a plant. Environmental tolerance properties (such as drought, salt, metal tolerance) are also desperately needed in the developing world, these potential life-savers should come to the fore in a matter of years and are currently in the research pipeline.
An excellent example of a gene that has been successfully transplanted into a crop is that of Golden Rice. According to the World Health Organisation, about 250 million people worldwide are deficient in vitamin A, and 500,000 children go blind per year because of this deficiency. This is an especially bad problem in countries where rice is the staple food. Golden Rice has had three vitamin A biosynthetic pathway genes inserted into the plant giving the rice grain a distinct yellow/orange colour. Golden Rice has the potential to improve the lives of a great many people, it is an example of GM technology which makes a massive difference to human society, and it is only the first of many crops that will be available.
On a more commercial front, flowering plants contain a gene called 'chalcone synthase' which is a part of the biosynthetic pathway which creates pigment in petals. Researchers duplicated this gene in the genome of the plants which had the effect of cocking up the biochemical pathway somewhat so that less pigment is produced (an effect known as 'sense-suppression'). This method has been used upon chrysanthemums, enabling the creation of white flowers, and roses, creating light pink petals.
One thing that researchers can do nowadays is to check their gene of interest for similarities with anything from the human genome. If there is an ancestral gene that is common to both humans and your plant you don't really want it in there, as this increases the chance of undesirable effects, such as making the end product toxic, or inducing allergic reactions.
Transform the Plant
Once you have decided on both your plant and your gene, the next thing to do is to 'transform' it. That is to somehow get your gene in the genomic DNA of the plant in a working form, without messing up any other genes or gene complexes that are already working happily away in the plant already.
Most of the time, scientists don't change an embryo, leaf or any other recognisable part of a plant. Before you transform your plant you have to do something called 'tissue culture'. Basically, you get a chunk of the plant and put it in a dish containing all the nutrients the cells need to grow. From then you will get a green messy growing lump (called a 'callus'). It is the callus that is transformed.
The most common way of doing this is with the bacterium Agrobacterium tumerfaciens, or 'agrobacterium' for short, or 'agro' for shorter. Agrobacterium is a naturally-occurring and mischievous bacteria that goes about inserting bits of its own DNA in plants! However, this is pretty useful if you have some DNA of your own (such as a pesticide-resistance gene) that you want to insert. All you have to do is get your DNA into the bacterium, which is quite easy, and then add it to your tissue culture. Sit back and have a well-earned beer while the bacteria do all the hard work.
An alternative way to transform a plant is the excitingly-named 'gene gun'. Rather disappointingly, it's not an alien death ray but a method that literally shoots microscopic gold spheres that are coated with the DNA that you want to insert into your plant. This sounds a bit random but it actually works strangely enough. Shoot enough DNA into enough cells and the DNA will be taken up into the genome of a small percentage of cells.
Adding the correct plant hormones to the tissue culture will make it grow different parts. You can grow shoots and root with different chemicals called auxins and gibberelins, and hey presto! You have a fully-fledged GM plant.
This isn't the end of the story though. For safety's sake you have to see whether you have inserted your gene into any other genes native to the plant, disabling it. Although the insertion of foreign genes into is a random procedure, biologists have ways that they can check to see precisely where the gene has inserted. You have to perform these experiments and thoroughly check your plant to see if any negative effects have come about because of the genetic modification. This mostly involves simply growing many transformed plants to full adulthood and thoroughly checking any unexpected changes in the plants phenotype (the physical expression of the genome). You can also screen the DNA of the GM plants to see exactly where the foreign DNA has been inserted. If you transform enough plants the chances are that there will be a certain percentage that have no ill effects from the modification and have the transgene inserted and working just as planned. This is very time-consuming, but nowhere near as time consuming as the field trials and all of the regulatory steps that are mandated by law. By the end of these processes, and a few million dollars later down the line, you should have your working, approved GM plant growing happily in a field.