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Serotonin is a compound that makes people’s brains feel pleasant. According to a recent study by Shu Qingying and his collaborators at Zhejiang University’s College of Agriculture, the pests also like serotonin. When pests feed on rice, the content of serotonin in the plant will increase. For pests, this will increase both the “mouthfeel” and “nutrition” of rice. This is the first time in the scientific community to reveal the relationship between serotonin and rice insect resistance. It will provide new ideas for the cultivation of rice with better resistance and the development of pest control strategies.

A related paper, Resistance of Rice to Insect Pests Mediated by Suppression of Serotonin Biosynthesis, was published on Nature Plants on May 7, 2018.

In May, rice in the fields will usher in a new round of trials: The brown planted beaks have set off one after another, and they gradually migrate from the south to the north to migrate to the paddy fields to absorb the sap of the leaf sheaths. The locusts sleep all year round in the fields and go through a winter hibernation. Soon it will be drilled into the stalks of rice plants to feed on the youngest rice leaf (Plutonium-II). This is the two most destructive pests in rice fields.

“When infested with pests, the plant organism secretes different chemicals.” Prof. Geng Yonggen of the Institute of Insects has long focused on the interaction mechanism between plant compounds and insects. He said that although plants do not seem to speak and move, they also have their own language and “weapons,” which is mainly achieved through chemical compounds.

Studies have found that the content of serotonin in rice increases when pests ingest rice. It is mainly responsible for the synthesis of a gene called CYP71A1. “When the pests invaded rice, the ‘switch’ to synthesize serotonin was opened,” said Shu Qingxi.

In order to explore the effects of serotonin on pests, Dr. Luo Ting is going to take on the job of a few insects. The first 15 brown planthoppers were counted and placed in a container containing two rice plants: one rice is natural wild rice, and the other is rice that knocked out the CYP71A1 gene. Luo Ting observes the number of brown planthoppers on rice every hour. “We have found an interesting phenomenon: The brown planthoppers that have been distributed uniformly have shown a clear separation after a certain period of time.” Luo Ting said: “Most of the brown planthoppers choose to go to wild-type rice.” The peak of the gap is: 12:3.

Obviously, the rice that had been knocked out of the CYP71A1 gene was “picked up” by pests. Because it can not increase the secretion of serotonin. The next puzzle is: Why do pests like serotonin?

Figure: The natural natural wild rice on the left; the rice on which the CYP71A1 gene is knocked out on the right

The study found that after ingesting more serotonin, the growth and development of the insects was accelerated and the body was more “strengthened”, which was particularly evident in the body of the locusts. “The worm is very smart. It not only knows how to ‘eat,’ but it can also make food more ‘nutritious and delicious’.” Shu Qingyun said that this is the wisdom of pests.

It turns out that serotonin is not the “anger” or “defense” expressed by rice, but the “betrayal” who is even more attached to the rice body enhances the combat effectiveness of pests. However, from the perspective of human needs, developing rice that is not loved by insects is the key to improving rice resistance and maintaining grain yield and quality.

In this regard, the research group made further investigation and found that in plants, the synthesis of serotonin and salicylic acid has a common source material – chorismate. “The synthesis of the two is negatively regulated,” said Yan Yonggen. “Like the two faucets that come from the same water pipe, when the water volume is the same, one faucet has a large amount of water, and the other has a small amount of water. On the other hand, the first author of this article, Dr. Lu Haiping, also found that the two compounds themselves can actively inhibit the activity of the other’s synthetic genes, such as salicylic acid can inhibit the opening of the CYP71A1 gene from reducing the serotonin content.

Salicylic acid is a known compound that can increase disease resistance in rice. “Previous studies have found that salicylic acid has an independent disease-fighting effect, but we found that it has a regulatory relationship with serotonin in the study,” said Yonggen, who said that when pests started the serotonin production line, they could have helped fight disease. The “yield” of salicylic acid is reduced. “This is another ‘secret’ for pests to invade rice.”

According to Shuqing Xu, serotonin and salicylic acid anabolic pathways are present in many plants. This study will inspire the breeding of insects in rice and other crops. “For example, we can increase the resistance to aphids by controlling the synthesis of wheat serotonin,” said Shu Qingxi.

This research was co-authored by Prof. Qingqing Shu (Institute of Crops), Prof. Yongxin Yan (Professor of Insects), and Professor Ye Gongyin (Insects) of the National Key Laboratory of Rice Biology, Zhejiang University, together with the Jiaxing Academy of Agricultural Sciences and Wubo Habitat. Seed Industry Research Institute Co., Ltd. and New Castle University (UK) jointly completed.

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