Scientists demystify the male insect “love” code

Small cabbage moth on green leafy vegetables (Courtesy of Zhejiang University)

Bacterial genes improve the courtship of male insects. (Photo courtesy of Zhejiang University)

The inheritance of insects is generally believed to be inherited from the direct line of parents, but many microorganisms quietly pass their genes to insects when they coexist with insects. This type of cross-species gene exchange, the horizontal transfer gene (HGT), is often overlooked by scientists, how do insects get “flying” foreign genes? What effect do these genes have on insect survival?

On July 18, Cell published the results of corresponding authors such as Shen Xingxing, a researcher at the School of Agriculture and Biotechnology of Zhejiang University, Huang Jianhua, and Antonis Rokas, a professor at Vanderbilt University.

After years of research, the research team pointed out that there are a large number of horizontally transferred genes in the insect genome and found that “flying” foreign genes play an important role in insect courtship.

After hundreds of millions of years of evolution, how many horizontal transfer genes have been acquired by insects? With this scientific question in mind, the researchers conducted large-scale identification and screening of horizontally transferred genes.

The researchers conducted systematic analysis and study of 218 high-quality insect genomes, including a variety of butterflies, moths, beetles, planthoppers, bees, etc., and conducted big data analysis and screening of nearly 500,000 genetic samples. “Sporadic horizontal gene transfer studies have been seen in the past, but such large-scale studies are rare, and the study has also developed a more accurate screening algorithm.” An anonymous reviewer of Cell noted.

A total of 1410 foreign horizontally transferred genes were identified in the study, many of which were first-reported. On average, Lepidoptera (e.g., cabbage moth, black-veined golden-spotted butterfly, etc.) obtained 16 HGT genes/species, Hemiptera (e.g., brown planthoppers, etc.) obtained 13 HGT genes/species, Coleoptera (e.g., Achilles, etc.) obtained 6 HGT genes/species, and Hymenoptera (e.g., Western bees, etc.) obtained 3 HGT genes/species.

From the source of the HGT gene, 79% of the HGT gene was obtained from bacteria, 13.8% from fungi, 2.6% from viruses, 3% from plants, and the remaining 1.6% of the source is unknown.

After hundreds of millions of years, why have these foreign genes not been cleaned up in insects and can take root in the insect genome?

“We found that horizontally transferred genes are accompanied by insect adaptive evolution, and their genetic structure and function also change, and during the evolution they obtain multiple duplicate introns from the recipient insect genome, thus avoiding being removed by insects and achieving the purpose of ‘survival’ on the insect genome.” Shen Xingxing said. The acquisition of introns, on the one hand, increases the length of the HGT gene to reach the average length of other insects’ own genes, and on the other hand, the expression level of the HGT gene rises, which is conducive to better playing their biological functions.

What role do these 1410 horizontally transferred genes, after years of erosion, play in the insect body? Functional analysis and validation studies were conducted on these horizontally transferred genes, and exciting discoveries were made.

The researchers first conducted a series of functional studies on the highest proportion of horizontally transferred genes, including LOC105383139 (the foreign gene obtained by both moths and butterflies). The knockout mutant of LOC105383139 was obtained by CRISPR-Cas9 gene editing technology, and the horizontally transferred gene LOC105383139 obtained from Listeria was found to have a special effect on adult male cabbage moths.

The researchers were surprised to find that compared with the wild-type cabbage moth, the number of offspring of the mutant cabbage moth decreased by about 70%, but the growth and development of the mutant cabbage moth, such as body length, feeding, reproductive organs, etc., were not affected.

What causes the drastic decrease in the number of mutant moth offspring? The researchers further verified through behavioral experiments and found that the courtship desire of the mutant cabbage moth male to the female was significantly reduced. So far, this study confirms that the HGT gene LOC105383139 helps to enhance the courtship behavior of males to females, and discovered a new mechanism of “adult beauty” in which bacteria help insects courtship. This is also the first report of the HGT gene influencing animal courtship behavior.

For the prospect of this research, Shen Xingxing introduced that from the study of moths and butterfly HGT genes, a “new key” for insect reproduction has been found, which provides a new idea for the green control of important agricultural pests in the future, and this mechanism that leads to a sharp decrease in the number of insect offspring has important and far-reaching practical significance for finding new targets and key links for pest control.

The study also provides a high-quality library of insect HGT genes that will help other researchers conduct studies on the biological function of insect-level transfer genes. In addition, the evolutionary pattern of HGT gene found in the study also provides important new perspectives for the study of biology and biodiversity.

The research has been supported by the National Natural Science Foundation of China and the key projects of international cooperation, and the special project of basic scientific research business expenses of central universities. (Source: China Science Daily Cui Xueqin)

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