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Molecular Evidence For Horizontal Gene Transfer Between Plants And Animals

by Waseem Iqbal
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In the first known evidence of horizontal gene transfer between a plant and an animal, a common pest known as the whitefly (Bemisia tabaci) acquired a gene from the one of the various plants it feeds on, researchers reported today (March 25) in Cell. The gene, BtPMaT1, protects the insects from phenolic glycosides, toxins that many plants produce to defend themselves against such pests, thus allowing the whiteflies to feast.

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“This study is seriously cool,” says Charles Davis, an evolutionary biologist at Harvard University who was not involved in the study. It “demonstrates yet another nice example of how horizontal gene transfer among eukaryotes confers evolutionary novelty.”

Horizontal gene transfer is the nonsexual swapping of genes between species. It’s been documented previously between single-celled organisms and even between some eukaryotes such as fungi and beetles. There are a number of ways that horizontal gene transfer can occur. Genetic material can be transferred via phages or other viruses, and some organisms may take up free DNA from the environment.

The research team didn’t start out looking for evidence of interspecies gene passing involving whiteflies, says coauthor Ted Turlings, a chemical ecologist at the Université de Neuchâtel. Turling’s colleague Youjun Zhang and his team at the Chinese Academy of Agricultural Sciences originally set out to understand how these pests manage to evade the defenses of so many plants. “[Whiteflies] cause diseases in plants,” says Turlings. They can devastate crops. “That’s why they are so economically extremely important throughout the whole world.”

Zhang’s lab started by scouring the whitefly’s genome to search for genes that help it resist the natural pesticides released by plants. After comparing its genome to similar insects that aren’t able to withstand the plant toxins, they zeroed in on BtPMaT1. They found that this gene encodes a protein that neutralizes phenolic glycosides. Next, the team went searching for the gene’s evolutionary roots using the National Center for Biotechnology Information (NCBI) databases of genomes. No other insects shared the gene or even one similar to it. It had to have come from somewhere else.

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Eventually, in one of the databases, they did find evidence of similar genes—but they were in plants, not other insects. The team suspects that a virus in a plant took up the gene about 35 million years ago, then a whitefly ate that infected plant. The virus transferred the gene to the insect’s genome, and it then became fixed in the population.

“It shows that evolution can include genes from other organisms that can help you to survive better,” says Turlings.

Once the scientists identified the gene and determined that it had come from plants, they turned their attention toward deactivating it. They genetically engineered tomato plants with the toxin to express RNA that interfered with the gene. When the insects fed on these plants, the protective gene was silenced, and the insects died. When a different insect, Myzus persicae, without the BtPMaT1 gene was allowed to feed on the same genetically engineered tomato plants, they were their mortality rates were unchanged, suggesting that researchers may be able to develop crops that are resistant to the whiteflies but that won’t cause new harm to other species.

Pamela Soltis, a plant biologist at the University of Florida who was not involved in the study, says in an email to The Scientist that “intriguing questions” are raised by the study, such as how and when the gene transfer occurred and, “how commonly has this process been involved in generating resistance in herbivores to plant chemistry?”

Source: J. Xia et al., “Whitefly hijacks a plant detoxification gene that neutralizes plant toxins,” Cell, doi:10.1016/j.cell.2021.02.014, 2021. & Emma Yasinski – The Scientist

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