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GM  3. Examples of genetically modifying a plant genome for enhanced characteristics - cloning plant cells, insect resistance, herbicide resistance, improvements in nutritional value of food

INDEX of biology notes on genetics and applications of GM biotechnology from agriculture to medicine


(3) Examples of genetically modifying a plant genome for enhanced characteristics

As we have seen, plants can be genetically modified to enhance desired characteristics.

GM technology allows the transfer of useful genes into plants, so they develop useful enhanced characteristics e.g. anti-pest or increased size of grain.

GM crops are controversial but genetic engineering is transforming crop production.

You can genes from all sorts of organisms, not necessarily plants, cut out a selected chromosomes-genes, and insert them into the cells of crop plants.

These crop plants are thus genetically modified and referred to as GM crops.

You can genetically engineer crop plants to be resistance to disease from e.g. viruses, increase crop yields, produce bigger and better quality fruit.

A GM potato has been produced that is resistant to potato blight, a disease caused by a fungus, that devastated the rural population of Ireland in the 1840s who heavily relied on the potato in their diet.

Note that when genes are transferred to plants, it must be done at an early stage of their development because older organisms have too many cells needing to be genetically modified.

The examples below describe techniques used in agriculture to produce crops with desirable characteristics that increase crop yields.

 

Example 1. Producing plant cell clones

Diagram showing the genetic modification of plant cells using a bacterium plasmid vector, and finally cloning the plant cells to produce a commercially viable plant on a large scale.

Scientists frequently use a bacterium call Agrobacterium fumefaciens to genetically modify plants.

The Agrobacterium fumefaciens bacterium invades plant cells and can insert its genes into the plant's genome (DNA).

genetic modification of plant cloning plant cells with desired trait gene inserted using a bacterium

With reference to the diagram above.

Stages 1. to 5.: A gene is taken from the cells of a herbicide resistant plant (B) and inserted into a plasmid extracted from the Agrobacterium fumefaciens bacteria (A).

The procedures use splicing genes to cut the DNA strands open and join them up to make the modified plasmid.  (see insulin production for even more details).

By this procedure, you can now introduce the plasmid vector into the bacterium.

Stage 6.: The genetically modified plasmid is inserted back into the bacterium.

Stage 7.: The bacterium, with the newly inserted gene, can then enter the target plant cells and genetically modifies the plant cell's genome.

You quite simply let the modified bacterium infect the plant cells, modifying their DNA.

Thus you can now clone the plant cells.

Stage 8.: BUT, you have to select the correctly modified cells which have taken up the gene and reject the rest of the cells.

After screening, the selected plant cells are then grown into plantlets in a tissue culture containing nutrients and growth hormones.

Stage 9.: The plantlets are then trialled to produce fully grown mature plants.

Initially in a greenhouse, if successful, full scale field trials using a much larger area.

The modified plant cells can then be used to grow mature plants with their newly acquired gene giving them the anti-herbicide characteristic.

 

Example 2.  Producing a crop plant with insect resistance

A bacterium called Bacillus thuringiensis produces a toxin (a protein) that is poisonous to insect larvae that feed on plant roots and the adults on the leaves, damaging the crops.

The gene in the bacterium that codes for the toxin is inserted into the genome of crops such as corn and cotton.

The crops produce the toxin protein in their stems and leaves giving the plants insect-resistance.

The toxic protein is specific to insect pests (important) and harmless towards to animals, including humans and other harmless insects - but the long-term effects of the genetically modified genome are unknown.

This method, in principle, is good for farming because it increases crop yield, less eaten by insects, and reduces the use of insecticides - less harmful chemicals in the environment e.g. using less insecticides is less damaging to ecosystems in the countryside.

BUT, there is often a BUT!

As the insects feed on the crops they are constantly exposed to the toxin, so that later generations of the susceptible insects may develop resistance to the toxin and no longer die from its effects - so farmers may have to use other insecticides.

Also, although it kills the caterpillar or larvae, that eat the crops, it only works on some orders of insects e.g. moths and butterflies - the most serious pests

Farmers can use other insecticides - but these are already being overused - one of the main reasons for the decline of bee populations in many countries.

(When writing this, I found from the internet, that toxin-resistant strains of insects are already evolving!).

 

Example 3. Development of 'Golden Rice' to increase nutritional value.

  • Increase the content of beta-carotene in golden rice, bananas or other crops to reduce vitamin A deficiency in humans.

  • A lack of vitamin A in the body can be fatal, but a GM crop may help this reduce this deficiency in some people's diet.

  • Beta-carotene is essential for our bodies to make vitamin A.

    • Without beta-carotene in our diet, we can't make vitamin A.

      • Vitamin A is a fat-soluble vitamin that is naturally present in many foods.

      • Vitamin A is important for normal vision, the immune system, and reproduction.

      • Vitamin A also helps the heart, lungs, kidneys, and other organs work properly.

  • Vitamin A deficiency is common in many Asian and African countries and can cause blindness.

  • This is due to too little beta-carotene or vitamin A in their diet e.g. there is too little in their traditional rice crops, so in these areas there is a problem of Vitamin A deficiency..

  • Golden rice is a GM rice whose genetic make-up contains two genes from other organisms which enable this variety of rice to produce sufficient quantities of beta-carotene.

    • The gene controlling beta-carotene production was obtained from carrot plants and inserted into the genome of rice plants.

  • With golden rice as part of their diet, the risk of vitamin A deficiency is reduced and less people are likely to go blind.

 

Example 4. Production of insect-resistant, herbicide-resistant and 'climate/weather' resistant crops

  • Crops can be genetically engineered to grow and survive in drought conditions - lack of water puts a big constraint on the quality and quantity of crop yields.

  • You can modify the genetic make-up of plants by inserting genes that  help plants be more resistant to certain 'pests' e.g. fungal attack or insects.

  • Weeds are a nuisance to a farmer, they use up nutrients in the soil and compete with the crop of e.g. grain, reducing the crop yield.

    • But, you can also make GM crops resistant to a herbicide being used to kill all weeds in the field of growing crops i.e. only the crop that you want survive and the weeds dies!

    • As the crop grows the field is sprayed with herbicide, the crop is unaffected and the weeds killed.

    • This sounds good, BUT there is considerable concern, with available scientific data to prove it, about the use and effect of herbicides and insecticides on the local ecology e.g. damage to wild flowers, and particularly insects like important pollinating bees.

      • In my locality I see very few wild flowers growing near fields cultivated using 'modern' agricultural methods.

  • All of these effects will help to increase the quality and yield of a crop - particularly important food crops like maize, wheat and barley.

  •  A gene that helps fish survive in cold water has been inserted into the genome of a tomato plant to help the plant survive in a colder climate i.e. the plant is able to cope with lower temperatures than the original plant.


Summary of learning objectives and key words or phrases

Understand the use examples of uses of genetically modified plant genome to enhanced desired characteristics - genetic traits involving cloning plant cells.

Know that crop genes can be modified to make them insect resistant, herbicide resistant, more weather resistant to climate change.

Know that golden rice improves the nutrition of people by reducing vitamin A deficiency.

  • Know and understand that genes can also be transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics.

    • Know that new genes can be transferred to crop plants.

    • Crops that have had their genes modified in this way are called genetically modified crops (GM crops).

  • Examples of genetically modified crops include ones that are resistant to insect attack, viruses, fungi or to herbicides.

    • This is all about increasing the quantity and quality of crops - insert genes into the plant's genome to increase the size and the quality of the grain.

    • Similarly, you can do the same for fruit plants to increase the quality (e.g. taste) and size of fruit.

    • Large quantities of crops are lost to disease and insect attack, so it make economic sense in principle.

    • One practical example is that if you can make a crop resistant to a herbicide that is used to kill weeds - weeds that compete for the soil nutrients, then you can kill the weeds by spraying without damaging the crops.

    • You can produce plants (fruit or grain) that are also resistant to diseases and insect attack to improve crop yields.

    • You can genetically engineer sheep to produce substances like drugs in their milk, which are used to treat certain human diseases.

    • Genetically modified crops generally show increased yields.

  • Appreciate concerns about GM crops include the effect on populations of wild flowers and insects, and uncertainty about the effects of eating GM crops on human health.

    • There is considerable public concern about GM crops eg are they harmful, are they as nutritious, are they reducing biodiversity, will they spread and multiply at the expense of native plants - out-compete for nutrients, will they cross-bread with native plants changing the gene pool,

    • GM crops of rice, and other basic grown foods, are seen as an economic way of feeding the growing poor populations of third world countries.

    • The idea behind GM crops is to increase yields and increase nutrition.

    • You can insert genes into crop cells so that they contain particular nutrients, whose deficiency can cause ill-health, or engineer a strain of wheat to contain more protein if meat is scarce.

  • So there are lots of possibilities and lots of controversies - so 'watch this GM space'


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