Chinese scientists use dengue fever virus to build safer gene-editing system

Chinese scientists have developed a gene-editing system for plants that draws on material from deadly viruses such as dengue fever to improve safety and efficiency.

Commonly used gene-editing systems such as CRISPR rely on DNA vectors but they run the risk of leaving behind foreign DNA that can lead to unintended mutations.

The new system, developed by researchers from the Chinese Academy of Science Institute of Genetics and Developmental Biology and biotechnology company Qi Biodesign, uses messenger RNA, which does not have that problem.

″While mRNA delivery systems offer a powerful method for achieving transgene-free genome editing, they remain inefficient and challenging in plants,″ the team wrote in a paper published in the peer-reviewed Plant Biotechnology Journal on February 10.

″Here we describe an efficient mRNA delivery system for plants with substantially improved editing efficiency.″

Viruses can improve the efficiency of the process because of the way they have evolved to pass things between hosts.

The enhanced delivery system was created using components from the dengue fever and tobacco mosaic viruses, and outperformed a widely used DNA plasmid-based delivery system.

It improved average editing efficiency by 4.3 times when used for rice and 3.5 times for wheat, according to the team led by the institute’s plant editing expert Caixia Gao.

Through whole genome sequencing the team also confirmed that – unlike mutant plants made with the plasmid system – those made using their system had no integrated foreign DNA.

″The optimised mRNA delivery system increases the flexibility and applicability of transgene-free genome editing in plants,″ the team said.

Gene-editing technology has revolutionised agriculture by enabling modifications to plant DNA that enhance desirable traits such as high yields.

Conventionally, gene-editing tools are delivered into cells using DNA vectors, which can lead to the random integration of pieces of DNA that can cause unintended mutations.

This has caused concern about the safety of genetically modified crops, which are banned in some countries.

″Transgene-free genome editing technology is valuable for reducing public concerns regarding the environmental and food safety of gene-edited products and so is crucial for the advancement of gene-edited crop breeding,″ the researchers said.

Ribonucleoprotein-based delivery systems, which use combinations of RNA and proteins, have been successfully used to edit lettuce, wheat, rice and soybeans.

However, creating these systems is time-consuming and complex, while systems using mRNA are easier to obtain and more scalable.

The team has previously created an mRNA-based delivery system called TECCRNA to knock out genes and perform precise single base edits in wheat.

To create an enhanced delivery system, this time the team chose to modify an mRNA construct using components from both the dengue fever and tobacco mosaic viruses, which helped improve its stability and efficiency.

As RNA can be prone to degradation, the team also found that coating the mRNA with the chemical protamine led to higher editing efficiency.

″Our strategy … has the potential to be applied to other plant species amenable to biolistic delivery, including major crops like maize, sorghum, soybean, barley and vegetative propagated crops, such as sugar cane and banana,″ the team said.

Biolistic delivery, a technique used by the team, is also known as particle bombardment and uses a ″gene gun″ to fire small metal particles coated in molecules such as DNA or RNA into cells.

″We believe that this improved mRNA delivery system will accelerate advances in plant genome editing and provide a useful tool for plant genetic improvement,″ they wrote.