Switzerland: CRISPR/Cas has limitations

So far, new breeding methods (»CRISPR/Cas«) have represented a golden future for crop production, offering plant breeding progress with unbeatable price-performance value. But research at ETH (Swiss Technical University) in Zurich indicates the CRISPR/Cas »gene shear« has its limitations: viruses can develop resistance to its action.

The Swiss researchers aimed to use the CRISPR/Cas to introduce resistance to virus disease in cassava, important as food crop in South America, Africa and Asia.  Around 20 % of the crop’s harvest losses are blamed on virus disease with no effective plant protection treatments currently available. Normally, the »gene shear« is applied as a molecular-biological tool to carry out precise alterations in the genome. However, CRISPR/Cas is originally an immune system with which bacteria protect themselves against viruses. The scientists wished to utilise this characteristic and establish this defence mechanism permanently in cassava. The result wasn’t what they wanted. Not one of the modified lines developed a higher resistance capacity against cassava African mosaic virus.

What had gone wrong? The genome analysis showed that the gene shear had been active and had cloven the relevant virus genes. But then resistance evolved in the virus. The technique produced mutations and, on top of this, certain repair mechanisms in the virus DNA actually reversed the result of the gene shear action.

The Swiss researchers regard the CRISPR/Cas application (gene editing) as gene technology. If one uses the gene shear as a tool, this also falls under the gene technology law in Europe, although there are signs of further development in how the technique is to be regarded.