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How is genetic engineering done in plants?

For years, by crossing, scientists have achieved plants with a desired characteristic after many generations. Biotechnology accelerates this process and allows to catch only the desired genes from a plant, achieving the expected results in only one generation. Genetic engineering allows us to do all this. In this article I will explain what it is and how does it work.

WHAT IS GENETIC ENGINEERING?

Genetic engineering is a branch of biotechnology that consists in modifying hereditary characteristics of an organism by altering its genetic material. Usually it is used to get that certain microorganisms, such as bacteria or viruses, increase the synthesis of compounds, form new compounds or adapt to different environment.

It is a safer and more efficient tool for improving species than traditional methods (crossing) as it eliminates much of the randomness. On the other hand, modern biotechnology also becomes a new technology that has the power to modify the attributes of living organisms by introducing genetic material prepared in vitro.

It could be defined as the set of methodologies to transfer genes from one organism to another and express them (to produce proteins for which these genes encode) in different organisms of the original organism. DNA which combines fragments of different organisms is called recombinant DNA. Consequently, genetic engineering’s techniques are called recombinant DNA techniques.

Currently there are more plant organisms genetically modified than animal organisms. For this reason I will explain genetic engineering based on plants.

GENETIC ENGINEERING vs. TRADITIONAL METHODS

This methodology has 3 key advantages compared with traditional methods of genetic improvement based on hybridization:

  • The genes could come from any specie (for example a bacteria’s gene can be incorporated in soy‘s genome).
  • At genetically improved plant you may introduce a single new gene preserving the remaining genes from the original plant to their offspring.
  • This modification process delays less the deadlines than improvement by crossbreeding.

With this way you can modify properties of plants more broadly, more accurate and faster.

In traditional crossing it generates a hybrid which combines randomly genes of both parental organisms, including the gene of interest encoding the desired trait. In contrast, biotechnology techniques only pass one or few genes which encode a specific trait known. The new plant has all the original genes of the plant and an introduced gene accurately and directed (Figure 1).

fig1ENG
Figure 1. (A) Traditional method where, by crossing, a new variety is obtained. This carries the gene of interest (red), but also another genes randomly. (B) With genetic engineering we obtain a new variety of commercial plant with the gene of interest (red) of any other species (Source: Mireia Ramos, All You Need is Biology)

METHODOLOGY OF GENETIC ENGINEERING

Obtaining a transgenic organism through genetic engineering techniques involves the participation of an organism who gives the gene of interest and a receptor organism who will express the desired quality. The steps and the process techniques are:

0/ DECIDE THE AIM: MAKE KNOCK IN OR KNOCK OUT

KNOCK OUT:

This technique is to remove the expression of a gene, replacing it with a mutated version of itself, this being a non-functional copy. It allows the gene is not expressed.

KNOCK IN:

It is the opposite of the knock out process. A gene is replaced by a modified version of itself, which produces a variation in the resulting function of it.

In medicine, the knock in technique has been used as a strategy to replace or mutate genes that cause diseases such as Huntington’s chorea, in order to create a successful therapy.

1/ DOUBLE CHECK THAT THERE IS A GENE CODING FOR THE CHARACTERISTIC OF INTEREST

Firstly, you have to check the characteristic of interest comes from a gene, as this will be easier to transfer to a living organism that does not.

2/ CLONING THE GENE OF INTEREST

It is a complex process, but outline the steps are the following:

  • Extract DNA
  • Find a gene among the genes of this DNA
  • Sequence it
  • Build the recombinant vector

The DNA of interest is inserted into a plasmid, a circular DNA molecule with autonomous replication. The plasmids of bacterial origin are the most used (Video 1).

Video 1. “Clonación de un gen en un plásmido vector”. Explaining the use of plasmids as a vector in the process of cloning (Source: YouTube)

The development of these techniques was possible by the discovery of restriction enzymes. These enzymes recognize specific sequences and cut the DNA by these points. The generated ends can be sealed with ligase enzyme and to obtain a new DNA molecule, it called recombinant DNA (Figure 2).

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Figure 2. (1) Plasmid’s DNA (2) DNA from another living organism (3a, 3b) The restriction enzyme cuts DNA (4) The restriction enzyme recognizes AATT sequence and cuts between A and T nucleotides (5) The two DNAs are contacted with the purpose of forming recombinant molecules (6) A ligase enzyme joins the DNA ends (Source: GeoPaloma)

3/ CHARACTERISE GENE OF INTEREST

If we know the gene sequence we can compare this sequence with known gene sequence through bioinformatics, provided to determine which gene looks and assign a possible function. So when we have predicted the function of cloned gene we confirm it in vivo, usually transferring it to a model organism.

4/ MODIFY GENE OF INTEREST

We can add (promoter, introns…) or mutate sequences inside the encoding region.

5/ TRANSFORMATION OF A LIVING ORGANISM WITH GENE OF INTEREST

When we have finished the gene building with the desired gene and the promoter, the recombinant DNA is inserted into the cells of the living organism that we want to modify.

6/ CHARACTERIZATION GMO

When we already have the GMO (Genetically Modified Organism) it is analysed from the molecular and biological point. In the molecular analysis it must demonstrate if you have one or more copies of the transgene or how and what tissues the gene is expressed. In the biological analysis it looks if it achieves the objective for which it was designed.

REFERENCES

MireiaRamos-angles

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