Pest uses stolen plant gene

The whitefly, which is around one millimeter in size, can attack over 600 different plant species. (Image: Jixing Xia and Zhaojiang Guo)

The “success story” of the dreaded whitefly is apparently based on an astonishing gene transfer, according to a study. Millions of years ago, the pests appropriated a genetic make-up from their victims that makes them resistant to vegetable poisons. As a result, the whitefly can safely feed on many different plant species, according to the scientists’ experiments.

They attack geranium, poinsettia and the like – many plant lovers also know the whitefly (Bemisia tabaci) from the windowsill. What only annoys us in the home and garden can, however, threaten the very existence of farmers: the whitefly is one of the most important insect pests in the cultivation of various crops worldwide. Both the winged adults and their larvae cause the damage: Similar to aphids, they prick pathways and suck in the sap. This has also given the parasite the alternative name of whitefly. In addition to the direct damage caused by the loss of nutrients, the parasites also transmit plant viruses and, through their excretions, also promote the growth of fungal pathogens.

A plant gene in an insect

In order to track down the fundamentals of the amazing adaptability of plant parasites and to uncover possible weak points, an international team of researchers is investigating the genetic characteristics of the whitefly. As they emphasize, what is remarkable about this pest is that it apparently does not care much about the defense reactions of many different plants. Plants are by no means completely helpless victims: in order to defend themselves against sucking parasites, they produce certain toxins that harm the insects. In order not to harm themselves, the plants have “self-protection genes” that ensure the production of substances that protect them from the effects of their own toxins, the scientists explain.

As they report, they have now made an astonishing discovery in the whitefly in this context: the insects apparently carry such a plant-based “self-protection gene” in their genetic make-up. According to them, the characteristics of the genetic makeup of BtPMaT1 show that it is not an original insect gene, because comparable hereditary factors only exist in plants. It must therefore have entered the genome of the whitefly through a so-called horizontal gene transfer from plants.

Based on certain genetic characteristics, the researchers were able to conclude that the insects acquired the gene around 35 million years ago. “To the best of our knowledge, this is the first documented example of the horizontal gene transfer of a functional gene from a plant to an insect,” says co-author Ted Turlings from the University of Neuchâtel. “According to our results, this gene, which neutralizes toxic compounds produced by the plant, is not found in any other species of insect,” says the scientist.

Foreign gene with protective function

Through experiments, the researchers were able to prove that the plant genetic makeup actually protects the whitefly from the toxins of its victims. To do this, they genetically engineered tomato plants that form RNA molecules that can specifically block the function of the BtPMaT1 gene in whitefly. “As soon as the pests fed on these plants and thus ingested the RNA, their BtPMaT1 gene was silenced, which led to one hundred percent mortality of the insects,” reports Turlings. In this way, the researchers were able to demonstrate the importance of the foreign gene: Without the detoxifying effect of BtPMaT1, the whitefly succumbs to the natural defense substances of the plants.

But how could this gene transfer, which looks like the result of a manipulation in a genetic engineering laboratory, have taken place naturally? The researchers assume that viruses were involved: “We suspect that a virus in a plant once picked up this BtPMaT1 gene and transferred it to the insect after it was ingested by a whitefly,” says Turlings. “This is an extremely unusual event,” emphasizes the researcher, “but when you think of millions of years and billions of individual insects, viruses and plants over time, such a gene transfer seems conceivable. And if the acquired gene is beneficial for the insects, then it is evolutionarily favored and can establish and spread, ”explains Turlings.

The researchers write that the astonishingly broad host range of the whitefly is thus apparently based on a “gene theft”. “One of the questions we asked ourselves was how did these insects acquire this incredible adaptability to bypass plant defenses. With our discovery, we have at least uncovered one reason for this, ”Turlings sums up.

Source: Cell Press, technical article: Cell: 10.1016 / j.cell.2021.02.014

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