An ideal pesticide would kill only pests, leaving all other creatures unharmed. Now biologists have engineered potatoes to be lethal to a major pest called the Colorado potato beetle but harmless to other species, no pesticide required.
Ralph Bock of the Max Planck Institute of Molecular Plant Physiology in Germany has genetically modified potatoes to produce RNA molecules that, when eaten, shut down an important gene in the beetle. The approach is based on a technique known as gene silencing or RNA interference.
鈥淐urrently there鈥檚 a lot of excitement about it,鈥� says Bock. 鈥淚鈥檓 quite optimistic that it will provide an additional weapon to deal with pest insects.鈥�
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The genes in DNA act by making proteins, but to do this, their instructions are first copied into single-strand RNA molecules. But if double-stranded RNA molecules are present in a cell, it is usually a sign of viral infection, and triggers the cell to destroy any RNA sequences matching this particular string of genetic code.
This defense system is easily tricked. To silence the activity of a particular gene in an organism鈥檚 cells so that it stops making proteins, all you need to do is introduce some double-stranded RNA that contains that gene鈥檚 code.
The difficult bit is getting RNAs into cells. In most animals, including us, any RNAs in the gut or bloodstream are quickly destroyed.
In the 2000s, researchers discovered that some insects absorb double-stranded RNAs from their guts. Simply feeding them such RNAs is enough to trigger gene silencing in much of their bodies.
Trials by several groups since have shown that can protect them from pests while leaving some closely related insects unharmed. But producing the vast quantities of RNAs needed to do this would be extremely expensive, says Bock.
One solution is to genetically modify plants to produce pest-targeting RNAs themselves, rather than spraying these onto them.聽A maize variety called SmartStax Pro that produces RNAs that target the western corn rootworm pest has been approved in several countries, but is yet to go on sale.
For the chop
There is a problem with this approach, however. Long bits of RNA are best for triggering gene silencing, but plant cells tend to chop these up into shorter pieces that don鈥檛 work as well, says Bock.
In 2015, his team overcame this problem by , the tiny compartments inside plant cells that are used for photosynthesis. High levels of long RNAs accumulate in the chloroplasts, which he has now found in the beetles that eat the plant.
The method is ready to transfer into any variety, says Bock, and a team in China is聽 engineering the trait into commercial varieties for field trials.
鈥淲e are testing the other properties of the potatoes, including yields and taste,鈥� says Jiang Zhang of Hubei University in China, who worked with Bock on testing the chloroplast method.
Antje Dietz-Pfeilstetter at the Institute for Biosafety in Plant Biotechnology in Germany doesn鈥檛 think this chloroplast-based approach raises new safety issues. But crops should still be evaluated on a case-by-case basis, to confirm that they don鈥檛 harm non-target species, she says.
A spokesperson for Bayer says that it plans to launch SmartStax Pro maize in the early 2020s pending further regulatory approvals.
搁别蹿别谤别苍肠别:听bioRxiv, DOI:
