Apr. 10, 2018
Conventional pesticides have achieved miracles in helping feed the world, but they have their drawbacks, so a team of scientists from the University of Helsinki and the French National Centre for Scientific Research (CNRS) are working on a more environmentally-friendly solution. Instead of toxic chemicals, the researchers are developing new ways to produce RNA-based vaccines that target specific pests without damaging the host plants.
According to the United States Department of Agriculture (USDA), 40 to 50 percent of crops in the developing world are lost to pests – even in the United States, the figure is up to 25 percent. If it weren't for pesticides, these figures would be far worse, with 70 percent of the food grown being lost.
Though pesticides have done much to combat hunger, such chemical countermeasures are a bit crude. Many kill or repel diseases, insects and weeds by very general means, and they have to be broadcast over large fields to be effective. This means that the crops themselves might be affected, as can innocent plants and animals, since the pesticides enter the general environment.
What the Helsinki/CNRS scientists are aiming at is a method that is much more focused. They want a means of treating specific plants without harming them, while attacking specific threats. The approach they've settled on is a vaccine based on double-strand RNA. That is, a ribonucleic acid biopolymer that is structurally very similar to DNA and is involved in all manner of cell processes, including the expression of genes.
The idea is that these RNA molecules can be sprayed directly onto plant leaves, eliminating the need for broadcast application. They are absorbed into the plant and when it is attacked, it triggers what is called RNA interference. This is a common defense mechanism found in many life forms that works by inhibiting gene expression in memory RNA strands by matching the RNA sequences of the vaccine and the pathogen.
To put it more simply, it's less like a general poison and more like a saboteur that hunts down targeted RNA strands and jams a spanner in the works. Among its various functions, RNA carries the instructions from the genes on how to assemble amino acids into proteins. With RNA interference, small sequences of RNA bind with the messenger RNA, preventing it from carrying out its proper function. The cells can't produce the needed proteins, everything is disrupted, and the pest dies.
Aside from being sprayed directly on leaves, the RNA vaccine has the advantage of being biodegradable. The RNA breaks down quickly in the wild, so it can't accumulate like some pesticides can. In addition, it doesn't in any way alter the genetic structure of the host, so it isn't as susceptible to anti-GMO regulations as altering the plants to produce the vaccine themselves. However, the team still has problems to overcome.
"The challenge in developing RNA-based vaccines to protect plants has involved the production of RNA molecules," says Dr. Minna Poranen of the University of Helsinki's Faculty of Biological and Environmental Sciences. "Double-stranded RNA molecules have been produced through chemical synthesis, both as drug molecules and for research purposes, but such production methods are inefficient and expensive for plant protection."
Poranen's team is currently working on bypassing laboratory synthesis by persuading bacteria to make the vaccine. This involves using the RNA amplification system of a bacteria-eating virus called a bacteriophage to produce the desired double-strand RNA sequences. Like other viruses, bacteriophages cannot carry out full biological functions by themselves. Instead, they rely on invading proper living cells for the machinery to reproduce. By exploiting this, the team was able to turn the bacteriophages into little factories to create the RNA for the vaccines.
How long it will take to make this practical is hard to say because the hurdles are legal as well as biological.
"It's difficult to predict when the vaccine will be made available because no relevant legislation exists yet," says Poranen.