Spray-on gene editing could make genetic modification easy


Genetically modifying plants could soon be almost as easy as spraying them with water. A new technique that uses DNA attached to nanoparticles could have a wide variety of uses, including changing the properties of crops while they are growing in fields. “It was so straightforward,” says Heather Whitney at the University of Bristol in the UK. “It was really surprising how easy it was.” Whitney and her team have so far tested their technique on various plants, including wheat, maize, barley and sorghum. They simply used an ordinary plant mister to spray leaves with water containing nanoparticles called carbon dots that were bound to DNA. The DNA, which codes for a fluorescent protein, got into cells in the plants’ leaves, prompting them to glow green under UV light. This is a huge advance on conventional methods for inserting DNA into plants, which aren’t as easy or widely applicable. But this DNA wasn’t incorporated into the cells’ genomes, so should break down over time. Whitney and her colleagues then took their technique a step further, using carbon dots bound to DNA coding for the CRISPR machinery used for genome editing. In this way, they were able to permanently edit the genomes of cells in the leaves they sprayed. The results have yet to be confirmed by other groups, but if it works, spray-on gene editing could speed up plant research. It could also lead to new ways of improving and protecting crops, and of turning plants into biofactories capable of making chemicals such as flavourings and pharmaceutical products. “It’s amazing,” says Ignacio Rubio Somoza at the Centre for Research in Agricultural Genomics in Spain, who now plans to try the method. “I think it’s a pretty great advance.”

Spray away

At present, the main tool for genetically engineering plants is a microbe called Agrobacterium. Researchers use it to insert new bits of DNA into plant genomes, but it only works in some plants and using it outside the laboratory would be impractical and risky. Another approach is to use a “gene gun” to force DNA into plant cells. However, this can damage plants and is difficult to do on a large scale. Many teams are working on better ways of modifying plants. Whitney decided to try using carbon dots created by her colleague Carmen Galan. Carbon dots, discovered in 2004, are ball-like particles of carbon less than 10 nanometres across, which can be attached to other molecules. These carbon dots can form when carbon compounds burn, and occur naturally. “We’ve found them in coffee, we’ve found them in soil,” says Galan. Galan makes red-fluorescent carbon dots for Whitney by heating sugars in a normal microwave oven. Next, she attaches a polymer called polyethylene glycol that attracts DNA molecules electrostatically. When sprayed on leaves, carbon dots get into nearly every cell on the leaf surface, and up to a third of these cells use the added DNA to make new proteins. Experiments by the team show that the carbon dots don’t seem to be toxic, and may even boost plant growth.

Safety concerns

So far, the team’s attempts to modify egg cells in plant ovaries and stem cells in growing shoots have failed. That is a disadvantage when it comes to creating new varieties of GM plants. However, it would make it safer to apply carbon dots to fields of plants because any modifications wouldn’t get passed on to future generations or spread among wild plants. “It’s quite an exciting paper,” says Markita Landry at the University of California, Berkeley, who recently got DNA into plant cells using carbon nanotubes. Landry’s team has to forcibly inject nanotube solution into leaves – spraying alone doesn’t work. Whitney’s research is at an early stage and many questions remain unanswered, such as how the carbon dots get into cells. “It’s such early days. There’s so much we don’t know,” says Whitney. “It might never be optimised to the point where it could be sprayed on fields.” Spray-on gene editing could be misused, for instance to make crops toxic. But Whitney points out that anyone who wanted to poison food could do it far more easily in other ways. As for whether spraying carbon dots into the environment could harm animals, more research is needed. Carbon dots can get into mammalian cells growing in a dish, says Galan, but they are mopped up by the immune system if they get into the body.

New Scientist, 1 November 2019
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