True crime story: how this insect stole a plant’s genes

Researchers have discovered that whiteflies figured out millions of years ago how to incorporate plant DNA into their genome. | Screencap via eurekalert.org/Jixing Xia and Zhaojiang Guo

Researchers discover that whiteflies figured out millions of years ago how to incorporate plant DNA into their genome

A Chinese research team has discovered that, 35 million years ago, aphid-like whiteflies got ahead of the curve on gene transfer and found a way to incorporate a portion of DNA from plants into their genome.

The plant’s gene provided toxins that it used to protect against insects, but the pests took advantage of the stolen gene, named BtPMaT1, to neutralize those toxins so they could feed safely.

The gene enables the whiteflies to detoxify phenolic glycosides, common plant defence compounds.

Whiteflies are actually not flies, but are related to aphids. Like aphids they suck phloem sap out of plants, and, more importantly, they spread plant viruses that can harm crops.

Professor Ted Turlings, chemical ecologist and entomologist at the University of Neuchâtel near Geneva, Switzerland, said the work was carried out at the Chinese Academy for Agricultural Science in Beijing.

“I was the adviser/supervisor. They stumbled upon the gene when they were studying the whitefly genome, looking for genes that are involved in resisting plant defences. When they found BtPMaT1 and looked for similar sequences in other organisms, they only found them in plants, no other insect.”

Turlings said it seems to be the first recorded example of the horizontal transfer of a functional gene from a plant to an insect. The plants likely used the gene within their own cells to store their noxious compounds in a harmless form so that they would not poison themselves. The whiteflies stole the defence gene, giving them the ability to detoxify the compound to their own advantage and source plant food.

The findings underscored an evolutionary scenario in which herbivores managed to harness the genetic toolkit of their host plants to develop resistance to plant defences. The findings also showed how to exploit this discovery for crop protection.

Whiteflies are a major global agricultural pest that attack at least 600 different species of plants and crops such as tomato, cotton, broccoli, cassava, cabbage, and melon.

“The main harm they do to the plants is through the spread of viruses,” said Turlings. “We speculate that those viruses have been involved in the transfer of the gene. It seems to be the most likely scenario, but it will be impossible to fully determine the process behind the acquisition of the gene by the whitefly.”

According to Turlings, the theory is that a virus within a plant may have taken up the BtPMaT1 gene. After being ingested by a whitefly, the virus did something or affected something inside the insect that led to the gene being integrated into the whitefly’s genome.

“Of course, this is an extremely unlikely event, but if you think about millions of years and billions of individual insects, viruses, and plants across time, once in a while this could happen and, if the acquired gene is a benefit to the insects, then it will be evolutionarily favoured and may spread,” he said.

But if this horizontal gene transfer happened then, so long ago, could it happen now?

A similar transfer of a gene to whiteflies was reported in the publication Nature and there is also a study that provides evidence for a plant gene in mosquitoes.

“One of the questions we’ve been asking ourselves is how these insects acquired these incredible adaptations to circumvent plant defences and, with this discovery, we have revealed at least one reason as to why,” said Turlings.

“Horizontal gene transfer is extremely rare. It is possible that something similar happened in another insect, but it is extremely unlikely. Only a limited number of insects have been studied so far.”

To unshackle the whitefly’s stolen gene and render it vulnerable to plant toxins, the Chinese research team developed a small RNA molecule that interferes with the BtPMaT1 gene, making it non-functional and making the whiteflies susceptible to a plant’s deadly compounds.

“The most exciting step of this design was when our colleagues genetically manipulated tomato plants to start producing the RNA molecule,” said Turlings in a news release. “Once the whiteflies fed on the tomatoes and ingested the plant-produced RNA, their BtPMaT1gene was silenced, causing 100 percent mortality of the insect but the genetic manipulation (of the plant) had no impact on the survival of other insects that were tested.”

Turlings said the approach could provide growers with plants fully resistant to whiteflies.

Going forward, the research will continue to focus on the genetics of the whitefly.

“We found a second, similar gene in whiteflies and we would like to determine its function,” he said. “We also think that the gene BtPMaT1 is also able to neutralize other plant defense compounds. We will explore this further and look for other genes in whiteflies and other insects.”

He added that because the gene only occurs in whiteflies and not in any other arthropod, this RNA transformation would not affect other insect species. He stressed that this must be confirmed with additional experiments.

Turlings said that with focused efforts to produce genetically modified crops that are able to silence the whitefly gene, this advance could function as a targeted strategy for pest control to combat agricultural devastation caused by whitefly populations.

“There are still some hurdles this method needs to get over, most notably the skepticism about using transgenic plants,” he said. “But, in the future, I do see this as a very clear way of controlling whiteflies because we now know exactly the mechanism behind it, and we are equipped to deal with possible changes that may arise in the whitefly gene.”

The research study was published in the journal Cell.

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