Genome-editing scissors will revolutionise plant breeding, yet a professor fears EU countries will get side-tracked
Oct. 4, 2018
Genome-editing is the most significant change in plant breeding since gene transfer, which was introduced in the 1990s. Legislators are now taking a stand on the approach to two different methods of engineering the traits of plant species.
What is the difference between a grain species that includes genes transferred from other species by human hand and a species whose own DNA has been subtly modified by man?
This issue has been under consideration for five years already – ever since gene-editing scissors were introduced to plant breeding.
Gene-editing scissors, or the CRSIPR-Cas method, enables the modification of genes: with the scissors, DNA sequences can be removed from or added to cells. The target gene in the cell can easily be cut with a specifically pinpointed enzyme.
This method, known as genome editing, is considered revolutionary in terms of treating hereditary human diseases. It is also being used in plant breeding.
“In the case of plant breeding, we are speaking specifically of the type of gene-editing that can also occur and indeed does occur in nature – such modifications can be found in a 10-hectare barley field that comprises some billion individual grains, each carrying a handful of natural mutations,” says Teemu Teeri, professor of plant breeding at the Faculty of Agriculture and Forestry, University of Helsinki.
Right now, both citizens and legislators strive to understand whether plants bred with the help of novel gene technologies come with risks to health and the environment.
“From the perspective of legislators, genome editing is challenging, since it is impossible to distinguish between genome-edited plants and natural mutations,” notes Teeri.
Teeri is one of the two authors of a report on new plant breeding technologies, submitted to the Committee for the Future of the Finnish Parliament in summer 2018. He is well versed in the history of genetically modified plants and explains why he thinks the EU’s stance on genome-edited plants, presented in summer 2018, is miscalculated.
Origins in the harnessing of plants
Farmers have always been interested in increasing cereal yields and finding varieties resistant to harsh environmental conditions. Indeed, humans have bred plants for as long as land has been cultivated.
The first hereditary modifications in cereal plants were the result of plant domestication. Among such changes was the trait of seeds no longer falling off, enabling farmers to store them for further use. This change came about unintendedly, since only the seeds that had not dropped off ended up in the crib, forming the next plant generation.
How is it possible to bend plant genes to human will in this way?
“The domestication of plants from wild varieties into those better suited for farming occurs at the expense of adaptation. In the end, cereal crops become entirely dependent on farmers,” Teeri states.
In other words, plants adapt in response to good care provided by farmers, which guarantees success for the next generation.
The next step in breeding was crossing and selection. In this method, the best specimens are crossed, after which those surpassing even their progenitors will be selected. This approach is relatively slow, in addition to which it eliminates genes from the plant genome.
If new genes are required for a variety, they can be gained by crossing with native varieties. Despite its slow nature, crossing and selection has produced good results, and it remains the most widely used breeding method.
Breeding transformed by gene transfer in the 1980s
In the 1980s, a major scientific breakthrough occurred in plant breeding. With the help of the gene transfer technique, genes could be transferred between organisms, revolutionising many fields, including medicine. For the first time ever, humans were able to develop organisms that would never come to being through natural selection. Transgenic organisms are known as genetically modified organisms (GMO).
The gene transfer method was introduced to plant variety breeding in the 1990s, a momentous occasion for the principles of traditional plant breeding. This transformation made it possible to transfer even animal or microbial genes to plants, which is why GM breeding has resulted in heated debate and opposition. Teeri, however, considers the technique safe.
“Based on over 25 years of experience, it can be unequivocally stated that the risks of the GM breeding technique are no greater than those of traditional breeding,” he says. Thanks to rigorous risk assessment, GM food can be considered even safer than regular food.
Currently, the most widely grown transgenic cereal plants indeed have genes of specifically bacterial origin in them. Through them, plants can be made increasingly resistant to pests and herbicides.
Gene transfer helps plants repel insects without chemicals. In such cases, a gene of the Bacillus thuringiensis bacterium has been transferred into the plants. This gene produces a protein affecting the intestines of pest insect larvae. Such insect-resistant GM crops include corn, soybean, cotton and rapeseed, whose total area under cultivation is globally approximately 100 million hectares.
Natural genetic modification?
According to Teeri, genome editing conducted with gene-editing scissors is similar to natural genetic modification. In most cases, the editing produces alleles that can in principle occur also in nature – the only difference is that mutations originating in the scissor method are planned in advance in a laboratory.
Gene function is influenced through selection also with more traditional methods of plant breeding, but that takes time.
One example is the breeding of rapeseed oil with a technique where the substances harmful to humans have been eliminated by selecting specimens that do not produce them. Today, the same process can be carried out quickly through the scissor method, targeting it directly at the best crop varieties.
Traditional plant breeding is often considered “natural”, while breeding conducted in laboratory conditions is seen as its opposite.
“Oftentimes, it is deceptive to think of non-GMO products as ‘natural’. This ignores the fact traditionally bred cereal varieties are themselves anything but natural,” says Teeri.
He also points out that traditional breeding is far from risk-free. For example, certain potato and celery varieties have been withdrawn from the market due to their high content of harmful chemical substances.
Determining the degree of naturalness in plant varieties resulting from various breeding methods is complicated also by the fact that even though biotechnology is used when engineering varieties with gene-editing scissors, the end result contains no foreign genes, as in transgenic varieties.
Green or red light from legislators?
In July 2018, the Court of Justice of the European Union decided that genome-edited varieties are considered GMO varieties in EU legislation. This means that the same type of risk assessment is expected for them as is for transgenic varieties, a view which is a grave disappointment to the scientific community. In practice, the gene-editing scissor technique is out of bounds for European plant breeders. As the population grows and climate changes, challenges in plant breeding are sizeable. In Teeri’s opinion, this is why curtailing breeding techniques is a detrimental decision.
“Gene transfer and genome editing are needed for increased genetic modification, which promotes advances in selective breeding. As it were, the world of plant breeding is trying to keep up with the Red Queen's race. In other words, we must proceed at full steam just to stay afloat in pest and disease control. New resistance genes are constantly needed as pathogens defeat old ones,” explains Teeri.
The changing climate is another challenge, demanding improved stress tolerance in cereal crops. The frequency of atypical growth conditions similar to the past summer is predicted to increase.
At the same time, a decision has been made in the United States to classify genome editing as a traditional plant breeding method. What this means in practice is that varieties will arrive from the United States to European markets that according to the new legislation are “illegal” in the EU, yet it is impossible to prove their illegal nature.
“European plant breeders will undoubtedly and without knowing use prohibited gene-edited plants in their breeding programmes when producing new varieties for European fields,” Teeri surmises.
"There is no point in enacting laws if compliance cannot be controlled."