The war between plants and animals isn't really fair. Fauna have the advantages of movement for a start. If that wasn't enough, whiteflies have pinched a gene from plants and used it to break down the toxins that prevent some animals from eating many leaves, according to a new paper published in Cell. Truly, this game is rigged.
Horizontal gene transfer is a common process among bacteria, where genes from one species, such as those for antibiotic resistance, are incorporated by another as if it was their own. This capacity to share genes is one of the reasons bacterial infections can be so hard to beat. Ferns share genes to a staggering degree, contributing to their survival while surrounded by plants with more developed reproductive mechanisms.
Animals are known to have received genes from symbiotic bacteria, but not from plants, so scientists at the Chinese Academy of Agricultural Sciences were surprised to find a plant gene in whiteflies. These agricultural pests pose a particular threat to greenhouses because most are so small they can squeeze in where their predators cannot, before breeding rapidly.
"You cannot find this gene, BtPMaT1, which neutralizes toxic compounds produced by the plant, in any other insect species." said Professor Ted Turlings of the University of Neuchâtel in a statement. "This seems to be the first recorded example of the horizontal gene transfer of a functional gene from a plant into an insect,"
Evolving the antidote to your own poisons and leaving it lying around for your enemies to steal doesn't seem the most cunning of plans. However, it is thought plants need BtPMaT1 to avoid poisoning themselves on their own toxins. Which was all great until the aphid-like whiteflies came along and incorporated the gene into their own DNA.
Whiteflies make up the Aleyrodidae family, which contains more than 1,500 species, but not all have the BtPMaT1 gene. Turlings and co-authors suspect the gene transferred around 35 million years ago, but certainly less than 82 million years ago when sweet potato whiteflies (Bemisia tabaci) that now possess the gene broke away from others that do not.
The direct transfer of a plant gene to an animal is hard to credit. Instead; "We think a virus within the plant may have taken up this BtPMaT1 gene and, after ingestion by a whitefly, the virus then must have done something inside the insect whereby that gene was integrated into the whiteflies genome," Turlings said. He acknowledges how unlikely this sequence of events is, particularly since the virus probably gained no benefit from the gene and didn’t keep it long. Nevertheless, whiteflies, viruses, and the plants they feed on are so abundant that even very rare things will happen now and then.
Considering their pest status, there is a market for anything that can make even some whiteflies less damaging, and Turlings’ co-authors think they have an answer. They’ve genetically manipulated tomatoes to produce a small RNA molecule that disrupts the BtPMaT1, exposing them to the phenolic glycosides that form one of the most common plant defenses. Whiteflies that fed on the engineered tomatoes had 100 percent mortality. Humans may yet rebalance the unfair war.