“It’s so clever,” says Naomi Pierce, an entomologist and evolutionary biologist at Harvard who wasn’t involved in the study. “It’s taking advantage of a defense that has been carefully honed by plants … I’m just contemplating how incredible it is.”
Genetic theft is very difficult to prove, and by all accounts, it appears to be somewhat rare. The evidence is generally circumstantial, and by the time scientists clue in, millions of years may have passed. “There’s really no way to know—none of us were there,” says Seemay Chou, a biochemist at UC San Francisco, who led the discovery of a similar phenomenon in ticks but wasn’t involved in the new study.
When grand genetic heists do occur, they can create evolutionary shortcuts, and blur the boundaries between organisms. The tree of life is often presented as full of discrete branches, spaced farther and farther apart. Every so often, however, two organisms come close enough to intersect, and leave relics of their intimacy in their genetic codes. In abducting its enemy’s antidote, the whitefly may have rapidly armed itself with a new weapon, skipping over the chore of creating the gene itself, and becoming a touch plantier in the process. The study’s authors think the insect may have even carried out its felony with an accomplice: a microbial smuggler ferrying bits of genetic material between multicellular hosts.
Typically, genes can be traced back in time, because ancestors tend to pass them down like heirlooms to the generations that follow. But the new study’s researchers, led by Youjun Zhang, a plant biologist at the Chinese Academy of Agricultural Sciences, noticed that this one didn’t follow the usual pattern. They found the gene that protects these bugs from poison in the genomes of only one close-knit group of species on the whitefly family tree, as if it had appeared out of nowhere. Curious about the gene’s origins, the researchers searched its sequence in a massive database. They found that no other insect genomes encode the gene, or anything that even vaguely resembles it.
But a version of the gene appears to be a fixture of many plant species—a hint that it might have hopped from one organism into an entirely different one.
These genome-jumping events are known as horizontal gene transfers. They’re common among bacteria, which swap genetic material willy-nilly, often as a sort of primitive pantomime of sex. Among eukaryotes such as plants and animals, though, they’re relatively rare. For another organism’s genes to integrate, foreign DNA must make its way through a creature’s complex body, and into a cell. It must breach the barriers of the nucleus, where genetic material is cloistered. It must assimilate itself into a new molecular context in a usable form, without diminishing the integrity of the genome that’s already there. It must accomplish all of this without being nuked or jettisoned by the host’s many defenses against unfamiliar matter.