Researchers use genetics to make precision pesticides

KENNEWICK — As researchers plumb the depths of biochemistry and genetics, they are discovering new ways to deal with the pests that plague agriculture.

In fact, discoveries in how RNA — ribonucleic acid — is turned on and off to produce the proteins needed by living organisms is beginning to bear fruit in a new kind of pesticide that can be made specifically to target one kind of pest.

“I’ll call them genetic solutions,” said Russ Groves, an entomologist and extension specialist at the University of Wisconsin-Madison. “Make no mistake, they’re not genetic modification, and these do not classify as GM.”

Groves, speaking at the Washington-Oregon Potato Conference in Kennewick on Jan. 26, outlined how a new pesticide based on RNA interference and being tested by Massachusetts-based Greenlight Biosciences can help farmers better fight the Colorado potato beetle.

DNA — deoxyribonucleic acid — is a long molecule that resides in the nucleus of each cell and is made up of matching base pairs of four basic molecules — adenine (A) and thymine (T), guanine (G) and cytosine (C) — wrapped around each other in a long, double helix. Combinations of these matching bases, as they are called, are used to create amino acids, which are then assembled into the proteins living cells need to live.

To create those amino acids, a special protein comes along and “unzips” a portion of the DNA molecule, matching each chemical base with its opposite — guanine with cytosine and adenine with, in the case of RNA, uracil — to make messenger RNA. That creation then moves out of the cell’s nucleus and into the ribosome, where the exposed bases are matched to corresponding amino acids that are then used to build proteins.

According to Groves, genetic modification typically inserts a new combination of bases into the DNA to allow a living cell to create a new protein. For example, genes from the Bacillus thuringiensis — commonly known as Bt — have been inserted into corn, cotton and sweet potatoes to produce a toxin lethal to caterpillars so the plants produce their own pesticide.

“Let’s say we inserted a gene that produces a protein that fluoresces green,” Groves said. “If we did it right, out will come messenger RNA with this green gene in the middle. It’ll go to the ribosome, and it’ll be translated right into the protein that foresees green.”

Cells have chemical signals to turn protein production on and off, Groves said, and that’s where RNA interference — of RNAi — comes in. Once a cell “decides” it has made enough messenger RNA to produce enough protein molecules, a double-strand of RNA in the shape of a hairpin is produced, and that tells the cell to start cutting up all the strands of RNA used to produce a particular protein.

“We call this post translational gene silencing,” Groves said. “This is RNA interference. RNA interference is going on in us all the time.”

Groves said this is becoming a useful tool for molecular biologists who want to shut down very specific protein expressions in targeted species of insects that, for example, make it impossible for a pest to smell and thus find its prey, or genes that produce fat and allow a bug to survive during the winter. Or, Groves said you could identify the genes that have allowed a pest to become resistant to a pesticide or other chemical.

“You could shut down something that results in lethality, and the insect could die,” he explained.

Groves described work Greenline Biosciences is doing on RNAi pesticide on Colorado potato beetles. The compound is sprayed on potato plants, is eaten by the pests, and as it moves into the insect’s body, it forces the beetle to stop eating. Eventually, Groves said, the beetles will starve to death.

“An adult insect might take three or four days to die. A larva will probably take a few days to die. But make no mistake in three, four or five hours, they quit feeding,” Groves said.

In tests conducted last summer, the fields treated with Greenlight’s product — which may be available for use in 2023 — look about the same as fields treated with normal pesticides, Groves said.

“You can see these defoliation percentages aren’t really that much different, you know, compared to say an industry standard,” he said. “And I mean, just outwardly, these plots (of land) look really good.”

The first of these RNAi compounds was developed against the Colorado potato beetle because it was easy to deliver, Groves said. Each pest would require a different approach, and researchers are still not sure what proteins to target in other pests or how best to deliver them.

“It hasn’t been worked out yet exactly how to deliver these tools into every insect,” he said.

Groves said RNAi pesticides have some very distinct advantages. They can be made pest-specific and process-specific, so an RNA protein designed for a potato beetle won’t affect honeybees or other beneficial insects. In fact, Groves said that in the fields where the RNAi pesticide was tested, biodiversity was actually improved when compared to a field where a broad spectrum pesticide was applied.

Second, RNAi molecules break down in the environment quickly, leaving little residue or even trace they were ever used — an important consideration as an increasing number of food processors and retailers are embracing “no detectable residue” standards to meet demand from health-conscious consumers.

In fact, the ability to produce RNAi strands that debilitate or kill pests could be genetically engineered into a plant, Groves said.

But Groves was emphatic — this is one tool out of many, and not a magic bullet that will solve every problem a grower has.

“This compound isn’t going to be like, save the world or anything,” Groves said. “It’s just going to be part of a toolkit, but it’s going to be a functional, really cool, and an actually environmentally sensitive tool.”

Charles H. Featherstone can be reached at cfeatherstone@columbiabasinherald.com.