New breeding techniques such as genome editing are driving plant research forward in leaps and bounds. They could provide answers to the current challenges facing agriculture and plant breeding, which include climate change and feeding the world's growing population. However, the July 2018 ruling of the European Court of Justice represents a setback for the use of the latest research results in Europe.
Robert Hoffie (27) has a close relationship with winter barley. The doctoral student at the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) in Gatersleben, Germany, has spent the last two years working on a vulnerability of the grain, a susceptibility to the yellow mosaic virus. In autumn, these viruses infect the roots on infected areas via soil fungi – with the result that leaves or entire plants die in the growth and flowering phase. For the farmer, this can mean yield losses of up to 50 percent.
Robert Hoffie wants to make the barley resistant to the virus. Using a new breeding method, he switches off a gene that makes the plant susceptible. This approach is part of a group of new techniques called genome editing or targeted mutagenesis. Farmers and breeders hope that this will make it possible to better face the current challenges in the agricultural sector. One of these is that fewer and fewer pesticides are permitted on the fields. This is also relevant for soil fungi, which transmit the virus to the barley. "Resistant varieties are the only chance," says Robert Hoffie. Although these already exist, some of the genetically very flexible viruses have already overcome this resistance. It's about being one step ahead of the virus.
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The challenge of global warming
Climate change also places new demands on cultivation. It is not just a matter of melting glaciers in Greenland or rising sea levels on the coasts of the Maldives. Climate change is also altering the regions where the world's bread grows in the fields, and its rice, rapeseed and corn: Europe, North America, Russia or China. In Central and Northern Europe, the "hot season" and drought of 2018 brought climate change to the attention of many people. Forests and moors burned, streams became trickles and were no longer navigable.
The agricultural sector was hit particularly hard. In Germany, the soil dried out deep down on around 80 percent of the arable area. This resulted in serious crop failures, with grain yields falling by 18.6 percent compared with the three-year average.
Nutrition for billions
Extreme weather conditions could endanger the global food situation, especially if the world population grows to 9.8 billion people by 2050, as forecast. To make matters worse, every year around 10 million hectares of arable land are lost worldwide due to erosion and salinisation, for example. in the future it will be all the more important to cultivate crops that can withstand climate change – and that are even more fertile than before.
Producing better harvests is one of the oldest goals of agriculture and plant breeding. Around the beginning of the 19th century, farmers in Germany produced about one tonne of wheat per hectare. Today it is more than seven. Continuously optimised cultivation and ever better seed made the increase possible. According to scientific estimates, about one third of the higher yields are due to successes in plant breeding. For centuries, breeders focused on selecting the best plants, from which new seeds were obtained and further propagated.
After the discovery of the laws of inheritance by Gregor Mendel around 150 years ago, plant breeding changed. Breeders began to cross plants with desired characteristics and to select from their offspring those which had the desired genetic combination. To this day, this method produces stable, high-performance varieties that are more robust, higher yielding and contain more desired ingredients. Cross-breeding was later refined into hybrid breeding. Two inbred lines, which differ strongly from each other, are crossed with each other. Their first generation descendants are characterised by particularly strong growth and are clearly superior to the "parents".
Molecular biological techniques
These breeding techniques can be complemented by what scientists like Robert Hoffie do in their laboratories. The foundations for today's most modern molecular biological methods were laid back in the 1930s, when scientists first irradiated seeds in order to alter their genetic make-up. This resulted in mutations with positive effects, which were then used for breeding. This traditional technique of unfocused mutagenesis is still widespread today. It is not just UV, gamma or X-ray radiation but also chemical substances that have long been used to induce positive changes in the genome of cultivated plants.
Further milestones in the history of breeding were the development of cell and tissue cultures that can be used to regenerate complete plants. The decoding of the complete genome of Arabidopsis and rice in 2000 marked the beginning of a completely new era of plant research and breeding. For the first time, it was possible not only to determine that one or other characteristic is pronounced, but also to precisely localise the genes responsible for that characteristic and investigate their function.
Without these developments, the work of researchers today would not be possible.
In the laboratory
Before Hoffie began his research, his colleagues from IPK Gatersleben and the neighbouring Julius Kühn Institute in Quedlinburg had already discovered a gene that influences the interaction between barley and the yellow mosaic virus. This gene, which makes barley susceptible to the virus, is "switched off" in the genome of the old Asian barley by a spontaneous mutation in nature.
Robert Hoffie specifically triggers this mutation in a susceptible variety in order to make his winter barley just as resistant. The young researcher's work starts at the computer: in the structure of the susceptibility gene, he searches for a site where he can disable it using molecular biological means. Once he has found it, he assembles a DNA molecule in the laboratory that does the work in the barley cells for him: this molecule contains the information to form a protein that is able to cut the DNA, and another molecule that guides this protein like a navigation system to the right place in the genome. Robert Hoffie transfers this piece of DNA into bacteria, which in turn transfer it into barley cells via a solution in a petri dish. Then he waits. While whole plants are regenerated from the barley cells using tissue culture, the cells produce tiny molecular tools using the transferred DNA information. You can picture them as like a pair of scissors with address labels. These gene scissors cut through the DNA of the susceptibility gene at a defined point in the cells. Then what Robert Hoffie intended happens: the cell's own mechanisms repair the cut. Sometimes errors occur during this repair: mutations. The most common result is that the susceptibility gene is "switched off".
From such an experiment, the scientist receives a good dozen plants with these desired mutations and propagates them further. Greenhouse tests with the yellow mosaic virus have now confirmed that Robert Hoffie's modified barley is resistant.
Breeding methods that save time and money
The revolutionary thing about such new methods is that scientists can for the first time precisely induce a certain gene modification that is no different from a mutation produced in the course of evolution since time immemorial. Furthermore, the application is much cheaper than the older mutagenesis techniques in use for decades based on radiation and chemical mutagens. These trigger random mutations and scientists must then analyse the DNA of thousands of plants to filter out the few with useful changes.
Another advantage of genome editing is that the new methods are faster than all other breeding methods.
So are the old methods obsolete? Not at all, says Robert Hoffie. "Genome editing techniques only work when a property is based on a single gene or a few genes. Cross-breeding will always remain a core component of breeding, for example when it comes to complex traits that are distributed over a large number of genes."
Whether the virus-resistant barley will make it to the field, however, is uncertain. Under European genetic engineering law, all plants resulting from the old, unfocused mutagenesis techniques are exempted from the special regulation and labelling of genetically modified organisms (GMOs). In its ruling of 25 July 2018, the European Court of Justice (ECJ) stated that plants developed with the new techniques of targeted mutagenesis do not fall under this exception and must therefore be strictly regulated as GMOs – just like those with foreign DNA.
Scientists and industry representatives criticise the ruling, above all because it puts Europe at a competitive disadvantage – both as a research location and for the seed industry. A GMO approval procedure can take up to 15 years – and it is uncertain whether the variety will actually be approved at the end. In other countries, such as the USA or Canada, genome edited plants are not considered genetically modified organisms per se.
Experts expect that the different legal regulations will also make it considerably more difficult to import agricultural products into the EU. The reason: there is no test method that could identify the breeding method of plants at the EU border. The transgenic GMOs with foreign DNA in circulation today are registered internationally and have clear distinguishing features from conventional varieties. A test can therefore prove their origin.
In contrast, mutagenesis methods cannot be detected, because their results are the same as changes in the genome that could also be caused by natural mutations, for example by sunlight. Moreover, due to their relatively low cost, the new methods are not only reserved for large corporations, but can also be applied by small and medium-sized breeders throughout the world, who may not necessarily be familiar with the intricacies of European law.
The first plants bred using targeted mutagenesis techniques are already nearing market maturity in the USA. However, there is still a long way to go before there are internationally uniform regulations.