Schematic diagram of the mechanism of broad host adaptability of whitefly. Just like the ancients' "spear of the child, the shield of the attacker", it is through this ingenious way of evolution that the whitefly obtains a wide range of host adaptability. Photo courtesy of Vegetables and Flowers of the Chinese Academy of Agricultural Sciences
"Nature, it's amazing!"
As a "veteran" of the agricultural science and technology front, Zhang Youjun, director of the Institute of Vegetables and Flowers of the Chinese Academy of Agricultural Sciences, will issue such an exclamation whenever there are some major discoveries. Now this latest discovery makes him exclaim "magical" again -
In the hundreds of millions of years of war between plants and insects, both sides have long had their own survival philosophy with the evolution of species: insects feed on plants and reproduce; plants will not sit still, and whenever insects attack, they will produce a large number of toxins as a "shield" for defense. However, this kind of biochemical shield produced only in the "wartime" needs to be destroyed in the "peacetime", otherwise it will eat its own body. Responsible for destruction is a gene called phenolic malondiacil transferase, which is the "spear" that kills the enemy. Between a "shield" and a "spear", the moat fortress of the Plant Empire was built.
Correspondingly, in the long war of species, cunning insects gradually developed the ability to destroy plant shields and found siege strategies. An insect named whitefly stole the "spear" of the killer on the plant and used it to attack the biochemical "shield" of the plant, so that every time it attacked the city, there was no disadvantage.
"Isn't this what the ancients in the Warring States period said, 'the spear of the son, the shield of the attacker'?" Zhang Youjun and his team members were extremely excited after discovering this magical phenomenon. He said that the insect, called the whitefly, had a wide range of host adaptability by stealing the plant's phenolic malonyltransferase gene, and was invincible in the plant insect war, and could infringe on more than 600 plant species.
This is one of the results of the research that Zhang Youjun's team has spent nearly 20 years tracking. On March 25, the international top academic journal "Cell" published this discovery, which is also the first paper in the field of agricultural pest research in China in the journal, which is of great significance.
"Super Pest"
"What useful is this discovery for real life?" In an interview with the reporter of China Youth Daily and China Youth Network, Zhang Youjun said that the discovery can provide a basis for the development of new plant-derived insecticides, that is, to provide a new idea for the research and development of accurate green prevention and control technology for the field of whitefly.
It all starts with who the whitefly are.
More than 100 years ago, whitefly was first discovered on Tobacco in Greece, hence the name. This small flying insect, which is smaller than a sesame seed and looks neither fierce nor ugly, has been recognized by the Food and Agriculture Organization of the United Nations as the second largest pest in the world as an invasive alien species, and the only "super pest" identified by the organization so far.
"The danger of whitefly even exceeds that of the first agricultural pest, the cotton bollworm." Zhang Youjun said that it not only causes direct damage to the host plant phloem juice by sucking it, but also secretes honeydew to induce phytomycosis to harm plants. What's more, as a supercarrier of the virus, whiteflies are able to spread extremely damaging plant virus diseases, causing billions of dollars in economic losses each year.
Taking China as an example, since the mid-to-late 1990s, whitefly have successively caused harm across the country, of which the production of vegetables, cotton and other crops is the most serious. In 2009, the yellowing of the tomato aspergillosis transmitted by whitefeds alone caused losses to China's tomato industry of more than 10 billion yuan. In Beijing, the damage caused by whitefly to cucumbers, tomatoes, eggplants, melons and zucchini can reach more than 70% in severe cases.
"It can eat almost anything, more than 600 species of plants are its 'lunch on the plate', and it is extremely adaptable, and it is easy to erupt." Zhang Youjun said.
For more than 100 years, people have relied mainly on pesticides for the treatment of whiteflies, but there is no way to cure it so far. What's even more frustrating is that in the face of these chemical controls, the cunning guy of the whitefly has evolved "resistance" and has now shown resistance to more than 50 pesticide active ingredients.
The reason is that some of the most basic cognitive problems have not been solved - people have never understood why whitefly can have such a wide range of host adaptability, and why they are banned.
Zhang Youjun told reporters that some insects only eat one plant, such as brown planthoppers only eat rice, which belongs to the monophagous nature; some can eat a variety of plants within a family or close to the family, such as small cabbage moths only eat cruciferous vegetable crops, called oligosicity; and some can eat a variety of plants of different families, such as whitefly, called polyphagous insects.
"Why do insects eat different plants, and the adaptability of multi-food pests is strong, how to control them?" Zhang Youjun said that feeding habits are obviously closely related to the population outbreak hazards of pests. In 1999, he led a team to explore the mystery of insect feeding habits, and two years later, he led the team to focus his research efforts on the host adaptability of whitefly and the mechanism of its outbreak.
Now, that secret has been uncovered – cross-species "theft".
Cross-species "stealing"
The so-called cross-species "theft" is that the whitefly "steals" the "spear" in the plant and becomes a "sharp weapon" used to attack the plant, making the plant empire unable to defend.
In 2013, Zhang Youjun's team completed the whole gene sequencing of whitefly for the first time, and the genes in the whitefly were subsequently exposed to humans.
At this time, the research team was surprised to find that there was a gene in the body of the whitefed lice that was obviously derived from the plant- the phenolic malonyltransferase gene. According to Guo Zhaojiang, the first author of the paper and deputy director of the Plant Protection Research Office of the Institute of Vegetables and Flowers of the Chinese Academy of Agricultural Sciences, this gene is the "spear" in the plants discovered by scientists later.
"How did this gene, which only occurs in plants and a small number of fungal microbes, appear in the 'belly' of whitefly?" Guo Zhao will say.
The scientific team further found that this enzyme is mainly in the midgut of the whitefly, and there is still the activity of the gene in plants, which has the ability to metabolize phenolic sugars. In other words, the gene transferred to the body of the whitefly is not only passed down from generation to generation, but can also play an important role - used to break through the "shield" of the plant to protect itself.
In this way, the whitefly completed a successful "theft", turning the "spear" of the plant into its own "spear". This process, known as horizontal gene transfer, is relative to vertical gene transfer— in which parental transmission is passed on to offspring— it breaks down the boundaries of kinship and complicates the possibility of gene flow.
"This discovery has excited a lot of young people on the team." Xia Jixing, co-first author of the paper and a postdoctoral fellow at the Institute of Vegetables and Flowers of the Chinese Academy of Agricultural Sciences, said that the "self-contradictory" fable that has been handed down to this day Chinese did not admit to appear in the war between insects and plants.
This is also the first time in more than 100 years since the birth of modern biology that human studies have confirmed the phenomenon of horizontal transfer of functional genes between plants and animals across species.
Ted Turlings, a chemical ecologist and entomologist at the University of Neuchâtel in Switzerland, said: "This study provides the first functional evidence internationally of plant gene level transfer to insects, a gene capable of metabolacidyltransferase that metabolacidates, a plant-based defensive toxin, is present only in whiteflies. ”
However, how the "spear" that originally belonged to the plant was obtained by whitefly, researchers have not yet found out exactly.
They speculated that this "theft" may have occurred in the process of repeated transmission between the whitefly and the plant by the plant virus carried by the whitefly. The time of occurrence may be 35 million to 86 million years ago, and the specific process needs to be further studied.
Curbing "SuperPowers"
The study didn't end there. Finding the reason why the whitefly is "rampant" in the plant world, researchers still have to find a way to overcome it.
According to Yang Zezhong, co-first author of the paper and a postdoctoral fellow at the Institute of Vegetables and Flowers of the Chinese Academy of Agricultural Sciences, the research team developed a strategy to crack the "super power" of whitefly theft, that is, using RNA to interfere with the phenolic malonyltransferase gene of whitefly to make it sensitive to this plant toxic compound.
Following this line of thinking, the research team constructed a transgenic tomato strain that expressed the hairpin RNA.
The results showed that the mortality rate of whitefed lice was 15.48% after eating wild tomatoes without pesticide action, while the mortality rate of whitefed lice was 93.35% after 7 days of eating genetically modified tomatoes.
"These data show that genetically modified tomato strains can effectively control whitefly." Yang Zezhong said. This means that in the future, some plants may no longer need to use pesticides to control whiteflies, and use RNA interference to make some genetically modified plants, or once and for all.
Of course, there are some obstacles to this approach, such as concerns about genetically modified crops.
"Will this genetically modified plant, which can deal with whitefly, be harmful to the human body?" Zhang Youjun will also be asked such words. His explanation was that the gene was a plant-derived gene, and that the plant itself had it—and from that point of view, it was completely natural and safe.
"Because we eat tomatoes and other plants have this gene, we just 'stole' this plant-derived gene from the whitefly and expressed it in the plant, so there is no safety problem." Zhang Youjun said.
"I'm sure this story contains substantial innovations, and that this paper will be of great interest to ecologists, evolutionary biologists, phytochemists, and people working on pest control." Roy Kirsch, a reviewer for the journal Cell, gave this review. He also added that the study covers everything from plant metabolic profiles to comparative genomes of insects and everything in between, delving into problem solving from different perspectives.
Behind this major discovery is the persistence of Zhang Youjun's team for 20 years.
Since 2001, Zhang Youjun has been exploring the host adaptation mechanism of whitefly. He told reporters that the entire scientific research team also suffered from problems such as "insufficient funding" and "cold disciplines", but in the end they all survived.
In the past 20 years, some members of the team have changed careers to engage in other jobs, but the group of masters and doctors who stayed in that year have become professors and associate professors of relevant domestic scientific research institutes today.
"This major achievement is not only the reward of the team members' 20 years of grinding a sword, but also the opportunity given by the development of genetic technology and the development of the times." Zhang Youjun said.
China Youth Daily, Reporter Qiu Chenhui Source: China Youth Daily ( 2021-03-30 12 edition)
Source: China Youth Daily