Conventional plant breeding uses mutations


The Topic

DNA is a carrier of heritable information; spontaneous mutations (i.e. changes) in DNA occur naturally in all living beings. They can be triggered by environmental factors, such as radiation (e.g. UV-light) or substances (e.g. environmental toxins).
These changes often lead to diseases in humans and animals and, therefore, preventive measures are often advised e.g. the avoidance of certain substances or using protection against the effects of sunlight and radiation.

In plant breeding these mutations are often considered to be desirable: Mutations can produce genetic variants that can provide plants with new positive traits, such as improved growth, larger fruit or resistance to certain environmental conditions.
Natural populations and cultivated varieties are screened to identify desirable mutations. These plants are then further propagated and bred to obtain an optimal combination of the desired genetic information.

Some breeders accelerate the mutation rate by using ionising radiation or chemical substances. The aim of this mutation procedure is an increase in genetic diversity that can be achieved in shorter periods of time than would happen naturally. Plants
that are impacted in their development or show unwanted traits are discarded.

Although it is often claimed that these mutations are completely random, this only partially true. Seen as a whole, they are not random at all when the results of spontaneous changes in the genome of a whole population are considered; they are, in
fact, subject to different control mechanisms.

Plants are able to protect themselves against mutations to some extent: There are diverse, natural mechanisms in the plant cells that ensure some control of spontaneous mutations. There are regions of the genome are especially protected: Natural mechanisms
of gene regulation, so-called epigenetics are responsible for this. These epigenetic mechanisms regulate whether a gene is “read” or not, and this is, therefore, called gene regulation. Epigenetics can lead to denser packing of distinct genomic
regions; this reduces gene activity in these specific regions of the DNA. Such regions are much more protected against external influence compared to more loosely packed regions.

There are also repair mechanisms that can restore the original state of the genome after the occurrence of mutations. Plants can duplicate chromosomes and gene regions in order to respond to environmental stimuli. They have “back-ups” in their genome,
which means that multiple gene copies can be found in the plant genome. If one copy is lost another copy can compensate for the loss.

“Jumping genes” (transposons) are classified as endogenous adaptation mechanisms that can copy their genomic sequences to another region in the DNA. There are different mechanisms influencing the frequency and the region where the genes are introduced
depending on the class of the transposable element.

As a result, plants have many ways of changing and at the same time protecting their genome. This is important: A population can remain resilient over millions of years and still be capable of adapting to changed environmental conditions within a
certain range.

Plants need a highly adaptive genome due to their immobility; whereas humans and animals are mobile, plants have to remain in one place and cannot move elsewhere to find better conditions. This means that plants need to adapt to the conditions in
their specific habitat as effectively as possible. In consequence, mutations and epigenetic mechanisms in the genome which are to some extent of bigger flexibility compared to those of humans and animals, are particularly important for their survival.

Plant breeders can use these mechanisms of genetic variability. Conventional breeding works with cells or, to be more precise, with the whole organism. Genetic engineering intervenes directly in the genome and bypasses mechanisms of natural inheritance.


What is the problem?

Some techniques that trigger mutations are regarded as more natural and more harmless than others. Whereas plants are continuously exposed to UV-light from the sun and this triggers mutations, there are other techniques available, including radiation
or exposure to highly effective chemicals. None of these techniques leave any trace inside the plants apart from the increase in the range of genomic changes. There is, however, some debate about whether all mutation techniques are harmless.

Plants originating from mutation breeding cannot always be used as food. In some cases, the content of harmful solanine might increase in plants belonging to species of the nightshade plant family (such as tomatoes or potatoes). An increased concentration
of gluten found in some types of grains is also still under discussion in this respect. Some breeding results are simply not suitable for sustainable agriculture, e.g. in cases where plants would need to be treated with increased amounts of pesticides
or fertiliser during cultivation.

Some experts claim that plants derived from mutation breeding should be investigated on a case-by-case basis. This is already done in Canada: Plants with certain new traits are risk assessed even if they were not genetically engineered. Basically,
spontaneously occurring mutations cannot be controlled as evolution and plant adaptation mechanisms cannot be subject to a legal regulation. Nevertheless, the individual results can be examined and plants and animals from conventional breeding
assessed if these show indications of risks to health or the environment. In the EU, plants derived from classical mutation breeding are exempted from regulation. On the other hand, plants and animals developed through genetic engineering are
assessed according to the EU guideline 2001/18. This includes, amongst others, “techniques, involving the insertion of nucleic acid molecules into an organism produced by whatever means outside an organism (...)”

There are good reasons for this: Genetic engineering is used to change DNA directly in the genome; such changes are not (or only partially) subject to naturally occurring biological mechanisms of inheritance. Additionally, these techniques are able
to circumvent and manipulate the mechanisms of gene regulation

Thus, these kinds of genetic engineering are completely different to techniques used in conventional breeding working with whole cells or organisms. Therefore, of genetic engineering can not be considered as a technical development which is simply
continuing previous methods of plant breeding. The results and their associated risks are very often remarkably different to conventional breeding, even where no new genes are introduced.

In brief, new genetic engineering techniques are very different to traditional breeding techniques in the depth of intervention:
Gene-editing techniques directly intervene in the cell nucleus, bypassing 'the rules' of gene regulation and inheritance. In contrast, conventional mutation breeding can speed up the biological mechanisms developed by evolution, but it does not break 'the rules'.


Further information

In regard to discussions on the legal classification of the new genetic engineering techniques, terminology has been used to create some confusion around the meaning of words such as mutagenesis. Furthermore, there has been an attempt to create the
impression that changes in the genome brought about by using the new technology are comparable those brought about by conventional breeding.

The reason: Genetically engineered products are subject to risk assessment and an approval process before they are allowed to be placed on the market. This process can be costly. The exact amount of money is not known as the industry has not published
any information in this respect. However, measured against the potential of this market these costs are insignificant: Documents submitted in the EU can also be submitted in the US, Canada, Brazil, Argentina, and Australia. Over the last few years,
a multi-billion dollar market has been generated particularly for patented genetically engineered soya, corn and cotton seeds developed and owned by huge companies. The argument over costs is simply as an excuse to question existing regulation.

It is important to regulate plants and animals developed using new methods of genetic engineering in the future. This would allow independent experts to assess these plants for risks and mean that reliable methods of identification were available.
The protection of humans and the environment must be given the very highest priority.


Further Information:

Table comparison: Differences between Genome editing and mutagenesis