In the first known example of horizontal gene transfer between a plant and an animal, a common pest known as whitefly (Bemisia tabaci) acquired a gene from one of the various plants it feeds on, researchers reported today (March 25) in cell. The gene, BtPMaT1protects the insects from phenolic glycosides, toxins that many plants produce to defend themselves against such pests, and thus enables the white flies to feast.
“This study is really cool,” says Charles Davis, an evolutionary biologist at Harvard University who was not involved in the study. It “shows another fine example of how horizontal gene transfer between eukaryotes confers evolutionary novelty.”
Horizontal gene transfer is the non-sexual exchange of genes between species. It has been documented between unicellular organisms and even between some eukaryotes such as fungi and beetles. There are a number of ways that horizontal gene transfer can take place. Genetic material can be transmitted through phages or other viruses, and some organisms can ingest free DNA from the environment.
The research team wasn’t looking for evidence of gene transfer between species involving whiteflies, says co-author Ted Turlings, a chemical ecologist at Université de Neuchâtel. Turling’s colleague Youjun Zhang and his team from the Chinese Academy of Agricultural Sciences originally wanted to understand how these pests manage to evade the defense of so many plants. “[Whiteflies] cause disease in plants, ”says Turlings. They can destroy crops. “That is why they are so important economically all over the world.”
Zhang’s lab began searching the whitefly genome to look for genes that would help it resist the natural pesticides released by plants. After comparing their genome to similar insects that could not withstand the plant toxins, they focused on it BtPMaT1. They found that this gene encodes a protein that neutralizes phenolic glycosides. The team then looked for the gene’s evolutionary roots using the National Center for Biotechnology Information (NCBI) genome databases. No other insects shared the gene or anything like it. It must have come from somewhere else.
Eventually, they found evidence of similar genes in one of the databases – but they were in plants, not other insects. The team suspects that a virus in a plant picked up the gene about 35 million years ago, then a whitefly ate the infected plant. The virus transferred the gene to the genome of the insect and was then fixed in the population.
“It shows that evolution can include genes from other organisms that can help you survive better,” says Turlings.
After the scientists identified the gene and determined that it came from plants, they turned their attention to deactivating it. They genetically engineered tomato plants with the toxin to express RNA that disrupted the gene. When the insects fed on these plants, the protective gene was silenced and the insects died. If another insect, Myzus persicae, without that BtPMaT1 The gene was allowed to feed on the same genetically modified tomato plants, whose death rate remained unchanged, suggesting that researchers may be able to develop plants that are resistant to the whitefly but do not cause new damage to other species.
Pamela Soltis, a plant biologist at the University of Florida who was not involved in the study, said in an email The scientist that the study raises “fascinating questions” as to how and when the gene transfer took place and “how often was this process involved in the creation of resistance in herbivores to plant chemistry?”
J. Xia et al., “Whitefly Hijacks a Plant Detoxification Gene That Neutralizes Plant Toxins”. cell, doi: 10.1016 / j.cell.2021.02.014, 2021.