In countless science fiction works, the Zerg have been portrayed as terrifying creatures, and after they devour other creatures, they will quickly acquire each other's characteristics, so as to evolve themselves, find their opponents' weaknesses, and invade and defeat their opponents faster. Do real-life bugs have similar abilities? On March 25, Beijing time, the international top journal "cell" published the latest paper of Zhang Youjun's team at the Institute of Vegetables and Flowers of the Chinese Academy of Agricultural Sciences online, and will be officially published in the form of a cover article on April 1. The paper explains the secret of the wide host adaptability of the world's only "super pest", the whitefly, and uncovers a molecular war between whitefly and a variety of plants that occurred between whitefly and a variety of plants dating back 35-86 million years.
Super recipes for "super pests"
On March 23, in the experimental greenhouse of the Institute of Vegetables and Flowers of the Chinese Academy of Agricultural Sciences, in a spaced insect-raising room, there were rows of shelves, each of which had multiple 40-centimeter-square cages, shrouded in white light veils, containing tomatoes, tobacco and other different plants. The leaves of each plant are crawling with dense white bugs, which are very small, less than 1 mm long, and on closer inspection, some are translucent, and have a pair of white wings.
This is the whitefly, one of the world's 100 invasive species, the world's second largest agricultural pest recognized by the World Food and Agriculture Organization, and the only insect in the world to be dubbed a "super pest". Its danger even exceeds that of the first largest agricultural pest, the cotton bollworm.
The whitefly is considered the second largest pest in the world by fao and is currently the only agricultural pest to be dubbed a "super pest". Courtesy of the Chinese Academy of Agricultural Sciences
Why are only whitefly called "super pests"? In the greenhouse of the Vegetable Institute, Zhang Youjun told reporters that this is related to its wide host adaptability and the hundreds of virus species it spreads. "Different insects have different recipes, such as cotton bollworms, which can eat more than 200 kinds of plants, and the grassland moth that has invaded in the past two years can eat more than 300 kinds of plants." These are very harmful agricultural pests. The diet of whitefly is more extensive than them, it can eat more than 600 kinds of plants, more importantly, it carries a lot of plant viruses, known to have more than 300 kinds, whitefly in the eating plants, will also spread the virus to plants, causing plant death, such as tomatoes, in 2009 in China outbreak of tomato yellowing aspergillomavirus disease, causing more than 10 billion huge losses."
The feeding habits of insects vary greatly
Insects are one of the oldest species on Earth, and according to archaeological findings, the earliest known insects may have existed on Earth 425 million years ago.
In the evolution of hundreds of millions of years, insects have evolved a variety of ability to adapt to the environment, such as super reproductive ability, the ability to resist temperature changes, drought, hunger and even human agents, and the ability to preserve genetic mutations that are beneficial to themselves, among which the ability to adapt to food is one of its important abilities for survival and spread.
"Just like human beings, some people love to eat rice, some people love to eat pasta, in science, this is called eating sex," Zhang Youjun said, "human attitudes to rice and pasta are different, it is just a preference, exchange, you can also eat." Insects have a more extreme feeding habit, and plants that are not in the diet can be fatal to them. Therefore, among insects, the difference in feeding habits is very obvious, some are monophagous insects, such as brown planthoppers, eat rice, and there are also polyphagous, such as whitefly, which can eat more than 600 kinds."
Weapons of war, spears and shields of plants
Why is there such a big difference? Zhang Youjun explained that this is related to the hundreds of millions of years of war between plants and insects in the process of evolution. "In the evolution of species, insects will eat plants, plants will not sit still, they will also resist. For example, there is a very important secondary metabolite in plants, phenolic sugar, which is produced by plants to fight insects. Phenolic sugar is harmful to insects, even poisonous, and insects may be poisoned when they eat phenolic sugar. This is equivalent to the plant creating a biochemical shield for itself to defend itself against insect invasion. ”
Phenolic sugar is not a necessity for plant growth, it is a weapon made by plants in the "war period", Zhang Youjun explained, "First of all, in different plants, the proportion of phenolic sugar is also different, some are relatively low, some are very high, such as tomatoes, the proportion of phenolic sugar in the leaves is as high as 3%, which makes there are very few insect species that harm tomatoes. Secondly, the phenolic sugar content in the plant is not fixed, because the phenolic sugar is not beneficial to the growth of the plant, too much phenolic sugar will increase the burden of the plant, so when the pest is fierce, the plant will enter the wartime state, synthesize more phenolic sugar, and make more weapons to resist the enemy insects. When pests decrease and enemies recede, phenolic sugars are metabolized and returned to their normal growth state. How do plants metabolize phenolic sugars? It also has a spear, with its own spear to crack its own shield, to achieve the purpose of the knife and gun into the warehouse, the horse put the South Mountain, this spear, called malondiyl transferase, English abbreviation pmat1, it is very important, control the level of phenolic sugar content in the plant. ”
Plants have a corresponding mechanism, and insects of course have their own means. During the long war, insects learned how to destroy plant shields, because only by breaking the opponent's defenses could they get food and survive. Zhang Youjun introduced, "Because there are many kinds of phenolic sugars, which means that the shields of plants are different, and the number of insects cracking shields determines whether their recipes are extensive or not, some can only crack one, that is, single food, and some can crack multiple, which is multi-food."
When humanity joins the war
The whitefly is undoubtedly a master of cracking plant shields and the victor in the billion-year-old war of plants and insects. This situation did not begin to change until humanity joined the war.
The earliest public reports of whitefly appeared in 1889, when this small bug was found on tobacco in Greece, and the name of the whitefly is derived from this.
In the more than 100 years since then, whiteflies have rapidly invaded the world, and there have been outbreaks of whitefly invasions in Africa, the Americas and Asia, and countless plants such as cotton, watermelon, tomato, beans, and flowers have suffered insect infestations.
In China, the earliest whitefly invasion phenomenon was found in the 1990s, when the invasion was type B whitefly, and by 2003, Zhang Youjun first found the invasion of type b whitefly in China, type b and type Q whitefly also have a wide range of recipes, but the ability to spread the virus is different, and the ability of type q whitefly to spread the virus is stronger and more harmful.
The host plant of the whitefly is more than 600 species, which can transmit more than 300 viruses. Courtesy of the Chinese Academy of Agricultural Sciences
For more than a hundred years, human beings have mainly relied on pesticides for the control of whiteflies. Zhang Youjun explained, "The previous method was mainly to prevent in advance, because the harm caused by the virus is irreversible, and once infected, there is almost no way to treat it." However, the ability of whitefly to produce resistance is also very strong, so our monitoring and prevention work is very difficult, we must monitor the mutation of whitefly in real time, remind the local area in time, change the pesticide type, and achieve the prevention and control effect."
However, such prevention and control is passive, Zhang Youjun said, "why can the whitefly crack the phenolic shield in so many kinds of plants, how its super ability came from, has not been known, which is why we can only passively control in the past."
The secret under genetic sequencing
As early as 2001, Zhang Youjun began to carry out the monitoring, early warning and prevention of whitefed across the country, which was complicated and passive, and the early results were not completely satisfactory. However, according to the pest characteristics of the insect, Zhang Youjun finally developed a set of comprehensive control technology for whitefly and promoted it in a large area across the country, achieved good control results, and won the second prize of the National Science and Technology Progress Award in 2008.
However, the mechanism behind the outbreak of whitefly to harm many crops remains unclear, and it was not until the sequencing of the whitefly gene was completed that the situation began to be reversed. In 2013, Zhang Youjun's team completed the work of sequencing the whole gene of whitefly for the first time, and the secret of the genes in the whitefly was exposed to the human eye for the first time.
"It was around the end of 2013, and after we had finished sequencing the gene, in the whitefly genome, we found a gene that was clearly derived from plants, namely pmat1, phenolic malonyltransferase, which was only found in plants and a small number of fungal microorganisms." Zhang Youjun said.
Experiments have found that pmat1 is mainly in the midgut of whitefly, and there is still the activity of this gene in plants, which has the ability to metabolize phenolic sugars.
Whitefly use btpmat1 to detoxify phytophenolic sugars in the midgut. Courtesy of the Chinese Academy of Agricultural Sciences
"We verified it in different ways, for example, there is a method, is to dissect the midgut part of the whitefly to do experiments, the body length of less than 1 mm of whitefly, of which the intestine is very small, it is difficult to do experiments, our team of more than 50 people, day and night dissected for 1 week, collected more than 10,000 whitefly midgut, and finally determined that its midguel protein, can indeed metabolize phenolic sugars." Of course, there are other methods, such as examining the feces (honeydew) of whiteflies to see if there are phenolic metabolites in it. In the end, these different methods came to the same conclusion. We named pmat1 in the body of the whitefly as btpmat1, which is an abbreviation of the Latin scientific name of the whitefly. ”
The strategic weapon of the whitefly, attacking the shield of the child with the spear of the child
This discovery is undoubtedly staggering, in science fiction works, the ability of the zerg to plunder the characteristics of other species, really exists?
"Chinese knows the parable of contradictions. This parable, in the war of insects and plants, really appeared. Zhang Youjun said, "In plants, pmat1 is the spear of the shield of plant metabolism phenolic sugar." Now, the whitefly has obtained this spear and becomes its weapon to conquer the plant's defenses, with the spear of the child, the shield of the attacker, and there is no disadvantage. ”
How did pmat1, the spear that originally belonged to the plant, get it by whitefly? There is no further discovery, Zhang Youjun used the word "theft", he and his team have speculated, may be the plant virus carried by the whitefly, in the process of repeated transmission between the whitefly and the plant, let the whitefly obtain this property, but this is not a conclusion, the real process is not yet known.
Another question has a preliminary answer, that is, when did the whitefly get this property? Zhang Youjun told reporters, "We analyzed the gene sequence and found that the time when the whitefly acquired this property was about 86 million years ago to 35 million years ago." This is because the whitefly has a near-source brother called the greenhouse whitefly, which differentiated about 86 million years later, and no pmat1 was found in the body. ”
86 million years ago, the earth was still in the late Cretaceous period, the mass extinction of organisms had not yet arrived, and dinosaurs were still the overlords of the planet. In the world of plants, the change of dynasties has been basically completed, and angiosperms have sprung up and gradually replaced the mainstream status of gymnosperms.
In such a world, the whitefly completed a successful "theft", turning the spear of the plant into its own spear.
So, will there be a similar phenomenon? Zhang Youjun said that the possibility may not be large, "We found this phenomenon for the first time in the body of whitefly, but in fact, this process was gradually formed over a long period of tens of millions of years, and it has a certain degree of chance, so there is no need to worry too much." ”
Bio-protection, weapons that strengthen plants
This feature is also far less frightening than in science fiction. When humans understand the secret of whitefly becoming a "super pest", the weapons of whitefly are no longer sharp, Zhang Youjun introduced, "In our experiments, by inhibiting the activity of pmat1, the weapon efficiency of the phenolic sugar metabolized by whitefly is reduced, or even ineffective, it can effectively eliminate whitefly, and the maximum can make the whitefly 100% dead." ”
Commenting on the finding, the cell reviewer said, "This study is an important advance in the field of plant-insect interaction research, expounds novel resistance mechanisms, and explains the reasons for the amazing host adaptability of whitefly to a variety of crops", and the results provide a new idea for the development of precise green control technology in the field of whitefly.
"In the past, the prevention and control of whiteflies, mainly through pesticides and other ways, was a passive defense," Zhang Youjun said, "in the future, we can regulate plants, so that plants synthesize new secondary metabolites, inhibit pmat1 in the body of whitefly, so that whitefly lose the ability to metabolize toxic phenolic sugars, so as to achieve the purpose of preventing and controlling whitefly." This is equivalent to giving the plant a better weapon, enhancing its own immunity and allowing it to fend off pests on its own. ”
According to reports, this is the first "cell" paper in the field of agricultural entomology research in China. The research has been funded by the National Key R&D Program, the National Natural Science Foundation of China, the Characteristic Vegetable Industry Technology System and the Science and Technology Innovation Project of the Chinese Academy of Agricultural Sciences. Moreover, the research results have applied for a national invention patent.
Beijing News reporter Zhou Huaizong photographed Wang Wei
Edited by Zhang Shujing Proofreader Li Xiangling