IT’S THE PERFECT PREMISE for a science fiction movie.
A seemingly unthreatening bug feeds on a plant that produces deadly toxins. An extremely rare gene crossover event occurs. The insect then acquires DNA from the plant and becomes a superbug, terrorizing people all over the globe.
WHAT’S NEW In a study published Thursday in the journal Cell, molecular biologists report finding this unique DNA transfer in the whitefly (B. tabachi). This is the first time scientists have observed such a rare gene crossover event between plant and animal.
Co-author Ted Turlings is a professor of chemical ecology at the University of Neuchâtel. “As far as we know, ours is the first example of horizontal transfer of a functional gene from plant to animal,” he tells Inverse.
Horizontal gene transfer occurs when a species receives genes from another species and incorporates those genes into its own DNA.
Although this kind of gene transfer occurs occasionally between bacteria, finding this kind of DNA crossover between multicellular organisms is highly uncommon, Turlings says.
The study hones in on the effects of the gene that the whitefly received from the plant: BtPMaT1.
HOW THEY DID IT — The scientists confirmed the presence of the defensive gene, BtPMaT1, by feeding whiteflies a diet containing the toxic phenolic glycosides. A control group received a solution without the compound.
The researchers also genetically modified tomato plants to see if they could suppress the whitefly’s expression of the BtPMaT1 gene and overcome its genetic defenses.
DIGGING INTO THE DETAILS — The whitefly evolved to capitalize on the effects of BtPMaT1, the study suggests.
Here’s how it works: The whitefly ingests toxic compounds, known as phenolic glycosides, when feeding on the tomato plant. BtPMaT1 effectively neutralizes these toxins, rendering them harmless to the whitefly.
“… OURS IS THE FIRST EXAMPLE OF HORIZONTAL TRANSFER OF A FUNCTIONAL GENE FROM PLANT TO ANIMAL.”
The gene produces an enzyme that attaches to a chemical group in the glucosides, preventing the toxic breakdown of the compound that would normally occur in the insect’s body. The specific expression of this gene — and how it neutralizes the toxic compounds — was found in the whitefly’s gut tissue.
By incorporating the plant’s DNA into its own genome, the whitefly can wield the plant’s own defense mechanisms against itself — an ironic tragedy of evolution.
“This discovery reveals an unexpected route by which B. tabaci has evolved its extraordinary ability to overcome the defenses of its host plants,” the study team writes.
The researchers liken the whitefly’s evolutionary strategy to the third-century Chinese philosopher, Han Fei, who reportedly said, “Attack your shield with your spear.’’
“Similar to the gist of this [Fei’s] story, we reveal here that whiteflies have adopted their opponent’s combat strategy to resist it,” the team writes.
WHY IT MATTERS — This is the first known finding of gene transfer from plant to animal.
As Turlings explains, it’s a “big deal.” The existence of horizontal gene transfer is a major departure from the underlying principles of gene theory, he explains.
“Genes are normally transferred from parents to offspring — vertically,” Turlings says.
“Horizontal gene transfer happens very rarely just by chance when accidentally something happens whereby the gene from one species ends up in another species.”
But just how did B. tabachi acquire this plant gene? It may have to do with an ancient virus, the study suggests. The scientists believe that a virus transported this gene from a plant into the whitefly, which Turlings calls “an extremely rare event.”
The discovery of horizontal gene transfer from plants to animals may have, in turn, enormous evolutionary implications.
“It illustrates a novel route for genetic change and evolution to occur,” Turlings says.
WHAT’S NEXT — In the future, the team wants to extend their findings to developing new pest control techniques.
B. tabachi whiteflies damage agricultural plants, like tomato and tobacco, by secreting a sticky substance known as honeydew and transmitting viruses to these plants. They can cause billions of dollars in damages each year, globally decimating entire crop yields.
But the researchers in this study think they may have found a solution: They were able to suppress the effects of the BtPMaT1 gene in whiteflies by genetically modifying tomato plants with a unique kind of double-stranded RNA.
“When the whiteflies feed on these transformed plants, they ingest the RNA, which then interferes [with] the gene,” Turlings says. “As a consequence, the whiteflies can no longer neutralize the phenolic glucosides and they all die.”
The scientists also found that the RNA method didn’t hurt other insects, such as aphids, making it a possible tool for targeted pest control of whiteflies. However, the scientists do caution that further research is needed before farmers start genetically modifying their tomato plants.
“This needs further investigation, but it may be a very effective way to make the plants resistant to whiteflies,” Turlings says.
Abstract: Plants protect themselves with a vast array of toxic secondary metabolites, yet most plants serve as food for insects. The evolutionary processes that allow herbivorous insects to resist plant defenses remain largely unknown.The whitefly Bemisia tabaci is a cosmopolitan, highly polyphagous agricultural pest that vectors several serious plant pathogenic viruses and is an excellent model to probe the molecular mechanisms involved in overcoming plant defenses. Here,we show that, through an exceptional horizontal gene transfer event, the whitefly has acquired the plant-derived phenolic glucoside malonyltransferase gene BtPMaT1. This gene enables whiteflies to neutralize phenolic glucosides.This was confirmed by genetically transforming tomato plants to produce small interfering RNAs that silence BtPMaT1, thus impairing the whiteflies’ detoxification ability.These findings reveal an evolutionary scenario whereby herbivores harness the genetic toolkit of their host plants to develop resistance to plant defenses and how this can be exploited for crop protection.