Stealing genes
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We’re used to the idea that genes get passed down the generations from parent to child - so-called vertical gene transfer, if you want to be technical about it. And for most types of multicellular organisms, that’s it - the only way to share genes in a population is to get to making babies. However, some microbes can spread their genes around through horizontal gene transfer, swapping bits of DNA directly with each other, like the example of plasmids in our previous story, but this ability was thought to be solely restricted to bacteria and other simple organisms.
However, this was the year that evidence emerged of this rule being broken, with the first known example of horizontal gene transfer - or gene theft - from plants to insects reported by an international team of scientists led by Youjun Zhang from the Chinese Academy of Agricultural Sciences.
The gene bandits of this story are whitefly. A close relative of aphids and among the most destructive agricultural pests on the planet, whitefly extract and eat sugar sap from plants, but while they are gobbling up their sweet treat, they excrete a sticky substance called honeydew, which allows mould to grow on the plant. They also act as vectors for plant pathogens and quickly develop resistance to pesticides, making them prolific crop killers.
It turns out that a bit of genetic thievery has helped whitefly to become one of the world’s biggest pests. Genetic analysis has revealed that the whitefly stole a gene called BtPMaT1 from its plant hosts millions of years ago. The gene in question encodes a protein that neutralises toxic phenolic glycosides, which plants produce to ward off insects. While the gene is important in plants to protect them from their own internally-produced pesticide, the stolen version in whiteflies enables them to produce an antidote to the toxin so they can munch away happily on plants that other insects avoid.
The protective gene found in whitefly is only seen in a small group of whitefly species and seems to have appeared from nowhere. No other whitefly or insects have any genes similar to BtPMaT1, which is only found in plants, so theft is the obvious explanation. Exactly how the whitefly stole the gene remains unclear, but it could have involved a smuggler like a virus. Zhang and the team are now working on ways to inhibit the stolen gene, making the whitefly susceptible to the toxin again and reducing their agricultural impact.
Genetic thievery and evolutionary shortcuts like this could be much more common than previously thought, as species battle against each other in arms races. But, just like pinning down the culprit of a long-gone crime, its occurrence can be difficult to prove. Advances in genomic sequencing and analysis are bringing us new insights all the time into the relationships between genes and species, and shedding light on their evolutionary origins, so who knows how many more genetic bandits may be out there?
References:
First known gene transfer from plant to insect identified, Nature
A Pesky Insect Took an Evolutionary Shortcut, The Atlantic
First Report of Horizontal Gene Transfer Between Plant and Animal, The Scientist
A plant gene may have helped whiteflies become a major pest, Science News
Plant gene found in insect, shields it from leaf toxins, ScienceDaily
