Ancient bacteria responsible for thousands of insect genes

Genes on permanent loan for hundreds of millions of years may be responsible for providing some species of insects with an evolutionary edge.

That’s a finding published in Cell by researchers from a team at Zhejiang University in Hangzhou, China, and Vanderbilt University, US, which investigated the genomes of 218 different insects. The study found hundreds of genes were passed on to modern insects due to gene transfer across biological kingdoms – predominantly from bacteria but also plants, viruses and other simple organisms.

It’s the latest finding from a growing body of research into how genes provide evolutionary benefit to species when they cross from organisms via a process called horizontal gene transfer.

What is horizontal gene transfer?

The transfer of genetic information is often considered in the context of sexual reproduction, where parents pass on their genes to offspring.

But genetic information doesn’t just swap in the sexual realm. Among single-celled organisms like bacteria, genetic information is often exchanged when individuals link with one another and transfer genes in a process called conjugation.

In simple terms, horizontal gene transfer refers to events in which genes skip across genetic boundaries between species and are incorporated into the DNA of a new species.

It’s this process that evolutionary biologist Xing-Xing Shen found has allowed a large amount of genetic information to jump across from plants and microbes into insect species.

Shen believes this has gifted insects a range of characteristics that are optimised for their survival – from nutritional and growth benefits to environmental adaptations.

“Previous studies have shown that horizontal gene transfer may have contributed to insect biodiversity,” Shen says. “But nobody knew how large a role it plays in this process, and since there are a lot of high-quality insect genomes available for our analysis, I thought that now is a good time to systematically investigate how prevalent HGT is in insects.”

Reserchers from zhejiang university in hangzhou look at evolutionary chart on whiteboard.
Credit: Yang Li Liu

Deciphering the gene code

Researchers studied genomes from 11 species-rich orders of insects, including 68 Hymenoptera (which includes ants, bees and wasps), 62 Diptera (flies), 39 Lepidoptera (butterflies and moths), 19 Coleoptera (beetles) and Hemiptera (true bugs), four Blattodea (cockroaches), two Thysanoptera (thrips), two Ephemeroptera (mayflies), and one each of the Orthoptera (grasshoppers and crickets), Phthiraptera (lice) and Siphonaptera (flea) orders.

It found numerous instances of horizontal gene transfer from bacteria, fungi, plants and viruses.

Among these, Shen and his colleagues found that butterflies and moths had the highest number of gene transfers (16 genes per species) on average.

Bacteria were the origin for the majority of transfers, although they found that in some species like the tiger mosquito (Aedes albopictus) it originated in plants, and the tawny crazy ant (Nylanderia fulva) from fungi.

“There were HGT events everywhere we looked, however, we don’t know whether these transfers of genes are beneficial to the insects, or even the functions for most of these genes,” Shen explains.

The functions of genes are not necessarily known and to understand the functions of these foreign sequences, Shen and colleague Jinahua Huang decided to remove one.

A gene called LOC105383139, which was transferred from Listeria to the common ancestor of moths and butterflies about 300 million years ago, repeatedly was the most widespread across the studied genomes.

The researchers decided to remove the gene from the DNA of cabbage moths (Plutella xylostella) and found mated pairs that had the gene ”knocked out” produced fewer viable offspring than those which had no modification.

“And then, we found that the gene influences the male courtship behaviour,” Huang says. “This gene was horizontally introduced into nearly all moths and butterflies from a donor in the bacterial genus Listeria and we saw those moths lacking this gene cannot produce many viable eggs.”

Considering cabbage moths are known pests to vegetable producers, the research team next plans to investigate whether altering LOC105383139 could be beneficial in agricultural pest control.

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