Some whiteflies use plant genes to neutralize toxins in their diet.Photo credit: Getty
A harmful agricultural pest owes its success to a gene stolen from its plant host millions of years ago.
The finding reported today in Cell1 is the first known example of a natural gene transfer from a plant to an insect. It also explains a reason why the whitefly Bemisia tabaci is so adept at eating plants: the gene it grew from plants allows it to neutralize a toxin that some plants produce to fight insects defend.
Early work suggests that inhibiting this gene can make whiteflies vulnerable to the toxin and is a potential way to control the pest. “This reveals a mechanism by which we can tip the scales back in favor of the plant,” says Andrew Gloss, who studies the interactions between plants and pests at the University of Chicago in Illinois. “It’s a remarkable example of how the study of evolution can reveal new approaches to applications like crop protection.”
The tiny whitefly, more related to aphids than flies, is causing agricultural havoc around the world. Bemisia tabaci is among the most destructive of plant pests: whiteflies and sugary sap made from hundreds of plant types, while excreting a sticky, sweet substance called honeydew, which acts as a breeding ground for mold. Whiteflies are also vectors for more than 100 pathogenic plant viruses.
Stolen genes
That some species of whitefly owe some of their predatory ability to genes from other organisms is not entirely surprising, given that genetic theft is common in the arms race between plants and their pests. Over millions of years, plants and insects have borrowed heavily from microbial genomes, sometimes using their newly acquired genes to develop defense or offensive strategies.
Some insects, like the coffee berry borer (Hypothenemus hampei), have plundered microbial genes to get more food from hard-to-digest plant cell walls2, and a wild relative of wheat stole a fungal gene to fight a fungal disease called head rot3. However, until now it was not known that plants and insects steal from each other.
Entomologist Youjun Zhang of the Chinese Academy of Agricultural Sciences in Beijing and his colleagues searched the genome of B. tabaci for stolen genes when they found one that apparently had developed in plants rather than other insects or microbes.
Further studies showed that the gene can transfer a chemical group to defense compounds called phenolic glycosides. Such compounds are made by many plants, including tomatoes, to repel pests. However, the modification caused by the Whitefly gene rendered the compounds harmless.
To test the hypothesis, the team constructed tomato plants to make a double-stranded RNA molecule that can disrupt expression of the Whitefly gene. Almost all whiteflies that later fed on these treated tomato plants died.
This result points to a new means of combating whitefly, says Jonathan Gershenzon, chemical ecologist at the Max Planck Institute for Chemical Ecology in Jena. “It offers a tremendous opportunity to be specific,” he says. “You could keep the whiteflies away, but not harm beneficial insects like pollinators.”
Fight plant pests
Gene transfer between species can be difficult to prove, says study co-author Ted Turlings, a chemical ecologist at the University of Neuchâtel in Switzerland. To do this, Zhang, Turlings, and their colleagues analyzed the sequences of similar genes in plants and found that the Whitefly gene was their evolutionary relationship. The team also performed analysis to show that the gene was integrated into the whitefly genome and was not the result of plant DNA contaminating samples.
The results were surprising but convincing, says Yannick Pauchet, a molecular entomologist, also at the Max Planck Institute for Chemical Ecology. “According to the data they provided, horizontal gene transfer is the most economical explanation,” he says.
But how the whitefly managed to steal a plant gene is unclear. One possibility, Turlings says, is that a virus acted as an intermediate, moving genetic material from a plant into the whitefly genome.
As researchers sequence more genomes, they may discover more examples of gene transfer between plants and animals, says Gloss.
“Insects that take the genes from the plants themselves are just the last piece of the arsenal that we haven’t found yet,” he says. “In the battle between plants and their insect pests or pathogens, genes are drawn from the whole tree of life.”
