The refusal to grow plants that are resistant to pests can be equated with the ban on resistant GM varieties.
The method of obtaining plants resistant to the pest Cotton scoop for biologists has long been not outlandish, it has already allowed the development of soybean, maize, potato, cotton and other crops that are resistant to this pest. However, today scientists strongly recommend not to abandon the cultivation of unsustainable varieties, and in some countries these recommendations have been adopted as a mandatory rule for growing sustainable plants at the state level. Under the cut, you can learn about the reasons for introducing this seemingly strange rule and, as usual, a lot of related interesting facts.
Opened cotton bolls. Beautiful, is not it?
The farmer has a large number of natural enemies, be it drought, floods or pests. And if the struggle with the elements is still problematic, then with the development of genetics and genetic engineering, easy-to-use methods of creating plants resistant to some herbicides, infections and pests have emerged.
It can be said without exaggeration that the voracious caterpillar of the Cotton Scoop is a real pain in the industrious sirloin of farmers all over the world. It causes significant damage to the planting of cotton, tomatoes, corn and tobacco, and also threatens the plantations of soybeans, peas, pumpkins and zucchini.
')
In the picture on the left, an adult cotton scoop; on the right - caterpillar-damaged cotton tomato scoops.
The traditional method of pest control is insecticides, that is, "poisons against insects." This method has a weak spot - insecticides are harmful not only for insects, but also for many other animals, including mammals. In addition, insecticides are not always selective against pests, so their use can have a negative effect on populations of harmless or even beneficial insects. However, towards the end of the 20th century, an elegant solution to this environmental problem emerged - scientists learned how to create cultivar varieties resistant to the insects eating them using genetic engineering.
The method of obtaining cotton-resistant Scoop-based plants is based on genetic modification, during which one of the variants of cry protein δ-toxin gene (read as “delta toxin”), which is synthesized by the bacterium Bacillus thuringiensis, is inserted into the genome of the crop plant we need. forming a dispute.
The three-dimensional structure of the N-terminal domain of the δ-toxin.
To be precise, the δ-toxin in disputes is not dangerous for insects, it is simply stored up to the desired moment in the form of protein crystals. That is, in fact, in disputes there is an inactive form - protoxin. But after the dispute enters the intestine of the pest, the most interesting begins:
At the same time, under normal conditions, cells carefully control the concentration of ions in their cytoplasm, because even a slight imbalance in the ion balance can have a most unfortunate effect on viability. Unfortunately for an insect, the δ-toxin cation channel is strong enough to arrange a real genocide of epithelial cells in its intestine. In turn, the destruction of the intestinal walls opens up the way for bacteria to the nutrient-rich hemolymph of the insect, where they do their dirty deed (hemolymph is similar to blood in insects and some other animals).
The cotton scoop caterpillar gnaws a hole in the cotton box. Goodbye harvest.
Plants in which the gene of the δ-toxin is inserted into the genome are designated using the prefix "Bt-" in honor of the bacterium B acillus t huringiensis , in which the toxin was found. For the first time, this sustainability mechanism was successfully applied by the Belgian company Plant Genetic Systems in 1985 (it was later acquired by Goder Biotechnology Bayer CropScience) in the process of creating Bt-tobacco insensitive to the pest, and the first The δ-toxin was the Bt potato variety Newleaf, developed by another Godzilla of the biotechnology market, the Monsanto company: it was given the green light in 1995.
However, the Monsanto initiative soon suffered a failure: first, large consumers like McDonald's and Wendy's refused to buy Bt potatoes, citing consumer skepticism, and in 2000, the largest North American french fries producers decided to boycott this raw material in their production facilities. The Japanese nailed the last nail to the lid of the coffin “Newleaf”: they flatly refused to import Bt potatoes, and when they found out that Bt potatoes were used in the production of snacks already imported from the United States to the country of the Rising Sun, they demanded to withdraw all the goods that had been shipped. As a result, in 2001, Monsanto decided to abandon the further promotion of the Newleaf variety and focus on genetic engineering wheat, corn, soybean and cotton, and here we must pay tribute to them: now more than 90% of the total soybeans grown in the US are genetic engineering. For corn, the figure is a bit more modest, but it also gives reason to rejoice over the producers - more than 60% of the total crop.
Bt-cotton is also not deprived of popularity - it is grown in huge quantities, for example, in the USA, Brazil and China. Therefore, scientists recently conducted large-scale studies of the impact of its mass plantings on the environment. Most of all in this area succeeded, of course, the Americans. The Chinese are just beginning to develop environmental control techniques, and Brazil is lagging behind these indicators in the wake of progress.
Americans first began to pay attention to an unexpected problem: it turned out that the history of bacteria resistant to antibiotics begins to repeat with a cotton scoop. If the field is planted with unstable plantings, then the proportion of insects resistant to δ-toxin does not exceed one percent. However, for obvious reasons, extensive planting of Bt-cultures leads to the fact that the genotype susceptible to the δ-toxin is quickly destroyed, and it is replaced by an evil caterpillar, which does not care much. It turns out that there is no point in switching to genetically modified Bt-plants, since very soon the fields will be infested with pests that the δ-toxin does not cause any harm.
First of all, you should pay attention to the fact that there are more than a dozen cry- genes (I remind you that the so-called δ-toxin genes are called). Toxins with different characteristics are encoded by different genes; therefore, resistance to the δ-toxin encoded by the cry4 gene does not mean the automatic resistance of the pest to all its other types. Therefore, in the USA and Australia, Bt cultures containing at least two cry genes are now often planted. Obviously, this does not solve the problem of super pests completely, but it certainly slows down the process of development of sustainable populations. Indeed, if 1 out of 100 pest has resistance to each of the two toxins, then only 1 out of 10,000 is resistant to both toxins at once.
However, there is a much more effective method of countering the emergence of populations of resistant pests. This technique, for example, is used in the USA and Australia, and it consists in planting Bt-varieties mixed with unmodified varieties. In such cases, plants without pest resistance are called “refuge”, which can be translated from English as a “safety zone”. That is, these plants serve to ensure that insects susceptible to toxins could exist in the fields, while they would mate with carriers of resistance genes and thereby “dilute” them. Here, the fact that insect-repellent insects have been given this “invulnerability” due to recessive homozygote plays a great part.
A brief explanation of what is "recessive" and "homozygote." Immediately I warn you that the narration in this explanation is very superficial, although it gives very close to the truth of the presentation.
So, the genes are in the chromosomes. As we know, diploid chromosome organisms have N pairs of homologous chromosomes (the word “diploid” just means that chromosomes have pairs). For example, a person has 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes.
23 pairs of human chromosomes: 22 pairs of autosomes and 2 types of sex chromosomes - X and Y. On a pair of autosomes, which is agreed to be considered the fourth, there are allelic genes of the enzyme alcohol dehydrogenase , which will be discussed below.
Each pair of homologous autosomes is a long double-stranded DNA molecule carrying essentially the same genes, or rather, different forms of the same genes (types of the same gene are called "alleles" ), while different alleles may have radically different effects at the phenotype level. For example, each person has two allelic alcohol dehydrogenase (ADH) enzyme genes (one for each chromosome in the fourth pair of chromosomes), which catalyzes the oxidation of alcohols to aldehydes and ketones, including the oxidation of ethanol. But some people are less fortunate than others. Thus, carriers of the ADH2 and ADH3 alleles of the ADH gene are at risk for the development of alcoholism.
The three-dimensional structure of the homodimer of alcohol dehydrogenase, the monomers of which are encoded by the allele of the adh5 gene in all its glory. The word "homodimer" means that the functional protein consists of two ("dimer") identical ("homo") monomers.
At the same time among the allelic genes can be distinguished dominant and recessive. The dominance of the allele means that its presence essentially encodes the trait, nothing depends on the gene on the homologous chromosome: either the second gene is also dominant, that is, the organism has no choice, or the second gene is recessive, and the recessivity just means dominant gene. Thus, the manifestation of a recessive trait is possible only when both alleles in the genome are recessive. Dominant alleles are usually denoted by capital letters, and recessive lowercase. Thus, there are 4 possible variants of the genotype: AA, Aa, aA, aa . At the same time, there is essentially no difference between “Aa” and “aA” , since the “A” gene dominates over the “a” gene. The genotypes "AA" and "aa" are called homozygous, and the genotype "Aa" is called heterozygous.
A typical scheme of the law of unlinked inheritance of characters , first documented by Gregor Mendel . The diagram shows what offspring of a heterozygous mom and dad flower will be. Allele "B" is dominant and determines the purple color of the flower, allele "b" recessive and determines the white color of the flower. As a result, only a quarter of the offspring is white, as it appears only in the “bb” genotype.
So, as mentioned above, under natural conditions, the majority of insects resistant to δ-toxin are owners of this trait due to recessive homozygote (let's call it “dd” ). It turns out that if a farmer supports a population of δ-toxin susceptible pests by planting “safety zones”, then the owners of recessive “dd” homozygotes can have progeny with a rather high probability with the owners of the “Dd” or “DD” genotypes defenseless before the δ-toxin . At the same time, one allele of the offspring receives from mom, and the other from dad, so when crossing “dd” x “Dd” only half of the offspring will be resistant to the δ-toxin, and when crossing “dd” x “DD” in the offspring there will be no sustainable individuals - they will all be “Dd” heterozygotes. Thanks to this simple method, farmers in the United States and Australia keep the proportion of pest-insensitive pests in the population at a constant low level, which usually does not exceed a few percent, and the yield is still higher than when using only non-Bt cotton -cultures.
The Chinese have chosen a different path: they do not plant Bt and non-Bt plants in the same field, but create fields planted entirely with Bt cotton next to the fields of non-Bt plants. The effectiveness of this technique was tested during a joint study of Chinese and American scientists, which lasted from 2010 to 2013. Statistics on changes in the prevalence of δ-toxin-resistant pests were carried out on agricultural lands located in northern China with a total area of ​​more than 27 million hectares, among which were 2.7 million hectares of Bt-cotton, and the rest of the crops were not carriers of δ-toxin genes. The experimentally obtained figures were compared with extreme situations: growing exclusively Bt-crops and the results obtained using the American "safety zones". The results for the situation with growing exclusively Bt-crops were obtained using mathematical models of population genetics . The results were published in the journal Nature Biotechnology .
The results of joint research on the effectiveness of the Chinese method of combating the spread of δ-toxin-resistant pests. The dots indicate plantations, the letters indicate the names of the relevant Chinese provinces. The colors of the dots reflect the prevalence of δ-toxin-resistant pests.
It can be seen that in the period from 2010 to 2013 the situation has worsened, and in some regions is already taking a threatening turn. If, as of 2010, the average number of pests immune to the δ-toxin was slightly less than 1% of their total number, then in 2013 in some regions it already reached 12%. At the same time, by the end of the reporting period, the presence of resistant pests was detected in those areas that were considered free from them in 2010. At the same time, the “safety zones” method used in the USA shows the best results: over the same period, the proportion of resistant pests should have grown to values ​​around 1.1%. True, it is worth noting that the Chinese method is much better than nothing: according to the mathematical model, when growing exclusively Bt-cotton in 2013, the proportion of pests immune to the δ-toxin would be 98%! To make matters worse, pests with dominant resistance genes are increasingly common on Chinese plantations.
Which of these can be concluded? The thoughtless use of genetic engineering can, in a very, very short time, negate all its advantages and farmers will have to return to insecticides. That is why today scientists are actively developing rational methods for conducting agriculture associated with genetic engineering.
Opened cotton bolls. Beautiful, is not it?
The farmer has a large number of natural enemies, be it drought, floods or pests. And if the struggle with the elements is still problematic, then with the development of genetics and genetic engineering, easy-to-use methods of creating plants resistant to some herbicides, infections and pests have emerged.
Who is guilty?
It can be said without exaggeration that the voracious caterpillar of the Cotton Scoop is a real pain in the industrious sirloin of farmers all over the world. It causes significant damage to the planting of cotton, tomatoes, corn and tobacco, and also threatens the plantations of soybeans, peas, pumpkins and zucchini.
')
In the picture on the left, an adult cotton scoop; on the right - caterpillar-damaged cotton tomato scoops.
The traditional method of pest control is insecticides, that is, "poisons against insects." This method has a weak spot - insecticides are harmful not only for insects, but also for many other animals, including mammals. In addition, insecticides are not always selective against pests, so their use can have a negative effect on populations of harmless or even beneficial insects. However, towards the end of the 20th century, an elegant solution to this environmental problem emerged - scientists learned how to create cultivar varieties resistant to the insects eating them using genetic engineering.
The method of obtaining cotton-resistant Scoop-based plants is based on genetic modification, during which one of the variants of cry protein δ-toxin gene (read as “delta toxin”), which is synthesized by the bacterium Bacillus thuringiensis, is inserted into the genome of the crop plant we need. forming a dispute.
The three-dimensional structure of the N-terminal domain of the δ-toxin.
To be precise, the δ-toxin in disputes is not dangerous for insects, it is simply stored up to the desired moment in the form of protein crystals. That is, in fact, in disputes there is an inactive form - protoxin. But after the dispute enters the intestine of the pest, the most interesting begins:
- First, the alkaline pH values ​​present in the intestine (about 10) lead to the dissolution of protein crystals;
- Then the enzymes of the digestive system cut harmless protoxin in such a way that one of its fragments gains the ability to interact with receptors that are located on the epithelial cells of the intestine;
- Interaction with the receptor leads to another change, but this time only the spatial structure (conformation) of the fragment interacting with the receptor changes. The resulting protein is the active toxin;
- Finally, a change in conformation leads to the fact that the toxin begins to form cationic channels in the epithelial cells of the intestine.
At the same time, under normal conditions, cells carefully control the concentration of ions in their cytoplasm, because even a slight imbalance in the ion balance can have a most unfortunate effect on viability. Unfortunately for an insect, the δ-toxin cation channel is strong enough to arrange a real genocide of epithelial cells in its intestine. In turn, the destruction of the intestinal walls opens up the way for bacteria to the nutrient-rich hemolymph of the insect, where they do their dirty deed (hemolymph is similar to blood in insects and some other animals).
The cotton scoop caterpillar gnaws a hole in the cotton box. Goodbye harvest.
Plants in which the gene of the δ-toxin is inserted into the genome are designated using the prefix "Bt-" in honor of the bacterium B acillus t huringiensis , in which the toxin was found. For the first time, this sustainability mechanism was successfully applied by the Belgian company Plant Genetic Systems in 1985 (it was later acquired by Goder Biotechnology Bayer CropScience) in the process of creating Bt-tobacco insensitive to the pest, and the first The δ-toxin was the Bt potato variety Newleaf, developed by another Godzilla of the biotechnology market, the Monsanto company: it was given the green light in 1995.
However, the Monsanto initiative soon suffered a failure: first, large consumers like McDonald's and Wendy's refused to buy Bt potatoes, citing consumer skepticism, and in 2000, the largest North American french fries producers decided to boycott this raw material in their production facilities. The Japanese nailed the last nail to the lid of the coffin “Newleaf”: they flatly refused to import Bt potatoes, and when they found out that Bt potatoes were used in the production of snacks already imported from the United States to the country of the Rising Sun, they demanded to withdraw all the goods that had been shipped. As a result, in 2001, Monsanto decided to abandon the further promotion of the Newleaf variety and focus on genetic engineering wheat, corn, soybean and cotton, and here we must pay tribute to them: now more than 90% of the total soybeans grown in the US are genetic engineering. For corn, the figure is a bit more modest, but it also gives reason to rejoice over the producers - more than 60% of the total crop.
Bt-cotton is also not deprived of popularity - it is grown in huge quantities, for example, in the USA, Brazil and China. Therefore, scientists recently conducted large-scale studies of the impact of its mass plantings on the environment. Most of all in this area succeeded, of course, the Americans. The Chinese are just beginning to develop environmental control techniques, and Brazil is lagging behind these indicators in the wake of progress.
Americans first began to pay attention to an unexpected problem: it turned out that the history of bacteria resistant to antibiotics begins to repeat with a cotton scoop. If the field is planted with unstable plantings, then the proportion of insects resistant to δ-toxin does not exceed one percent. However, for obvious reasons, extensive planting of Bt-cultures leads to the fact that the genotype susceptible to the δ-toxin is quickly destroyed, and it is replaced by an evil caterpillar, which does not care much. It turns out that there is no point in switching to genetically modified Bt-plants, since very soon the fields will be infested with pests that the δ-toxin does not cause any harm.
What to do?
First of all, you should pay attention to the fact that there are more than a dozen cry- genes (I remind you that the so-called δ-toxin genes are called). Toxins with different characteristics are encoded by different genes; therefore, resistance to the δ-toxin encoded by the cry4 gene does not mean the automatic resistance of the pest to all its other types. Therefore, in the USA and Australia, Bt cultures containing at least two cry genes are now often planted. Obviously, this does not solve the problem of super pests completely, but it certainly slows down the process of development of sustainable populations. Indeed, if 1 out of 100 pest has resistance to each of the two toxins, then only 1 out of 10,000 is resistant to both toxins at once.
However, there is a much more effective method of countering the emergence of populations of resistant pests. This technique, for example, is used in the USA and Australia, and it consists in planting Bt-varieties mixed with unmodified varieties. In such cases, plants without pest resistance are called “refuge”, which can be translated from English as a “safety zone”. That is, these plants serve to ensure that insects susceptible to toxins could exist in the fields, while they would mate with carriers of resistance genes and thereby “dilute” them. Here, the fact that insect-repellent insects have been given this “invulnerability” due to recessive homozygote plays a great part.
A brief explanation of what is "recessive" and "homozygote." Immediately I warn you that the narration in this explanation is very superficial, although it gives very close to the truth of the presentation.
So, the genes are in the chromosomes. As we know, diploid chromosome organisms have N pairs of homologous chromosomes (the word “diploid” just means that chromosomes have pairs). For example, a person has 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes.
23 pairs of human chromosomes: 22 pairs of autosomes and 2 types of sex chromosomes - X and Y. On a pair of autosomes, which is agreed to be considered the fourth, there are allelic genes of the enzyme alcohol dehydrogenase , which will be discussed below.
Each pair of homologous autosomes is a long double-stranded DNA molecule carrying essentially the same genes, or rather, different forms of the same genes (types of the same gene are called "alleles" ), while different alleles may have radically different effects at the phenotype level. For example, each person has two allelic alcohol dehydrogenase (ADH) enzyme genes (one for each chromosome in the fourth pair of chromosomes), which catalyzes the oxidation of alcohols to aldehydes and ketones, including the oxidation of ethanol. But some people are less fortunate than others. Thus, carriers of the ADH2 and ADH3 alleles of the ADH gene are at risk for the development of alcoholism.
The three-dimensional structure of the homodimer of alcohol dehydrogenase, the monomers of which are encoded by the allele of the adh5 gene in all its glory. The word "homodimer" means that the functional protein consists of two ("dimer") identical ("homo") monomers.
At the same time among the allelic genes can be distinguished dominant and recessive. The dominance of the allele means that its presence essentially encodes the trait, nothing depends on the gene on the homologous chromosome: either the second gene is also dominant, that is, the organism has no choice, or the second gene is recessive, and the recessivity just means dominant gene. Thus, the manifestation of a recessive trait is possible only when both alleles in the genome are recessive. Dominant alleles are usually denoted by capital letters, and recessive lowercase. Thus, there are 4 possible variants of the genotype: AA, Aa, aA, aa . At the same time, there is essentially no difference between “Aa” and “aA” , since the “A” gene dominates over the “a” gene. The genotypes "AA" and "aa" are called homozygous, and the genotype "Aa" is called heterozygous.
A typical scheme of the law of unlinked inheritance of characters , first documented by Gregor Mendel . The diagram shows what offspring of a heterozygous mom and dad flower will be. Allele "B" is dominant and determines the purple color of the flower, allele "b" recessive and determines the white color of the flower. As a result, only a quarter of the offspring is white, as it appears only in the “bb” genotype.
So, as mentioned above, under natural conditions, the majority of insects resistant to δ-toxin are owners of this trait due to recessive homozygote (let's call it “dd” ). It turns out that if a farmer supports a population of δ-toxin susceptible pests by planting “safety zones”, then the owners of recessive “dd” homozygotes can have progeny with a rather high probability with the owners of the “Dd” or “DD” genotypes defenseless before the δ-toxin . At the same time, one allele of the offspring receives from mom, and the other from dad, so when crossing “dd” x “Dd” only half of the offspring will be resistant to the δ-toxin, and when crossing “dd” x “DD” in the offspring there will be no sustainable individuals - they will all be “Dd” heterozygotes. Thanks to this simple method, farmers in the United States and Australia keep the proportion of pest-insensitive pests in the population at a constant low level, which usually does not exceed a few percent, and the yield is still higher than when using only non-Bt cotton -cultures.
The Chinese have chosen a different path: they do not plant Bt and non-Bt plants in the same field, but create fields planted entirely with Bt cotton next to the fields of non-Bt plants. The effectiveness of this technique was tested during a joint study of Chinese and American scientists, which lasted from 2010 to 2013. Statistics on changes in the prevalence of δ-toxin-resistant pests were carried out on agricultural lands located in northern China with a total area of ​​more than 27 million hectares, among which were 2.7 million hectares of Bt-cotton, and the rest of the crops were not carriers of δ-toxin genes. The experimentally obtained figures were compared with extreme situations: growing exclusively Bt-crops and the results obtained using the American "safety zones". The results for the situation with growing exclusively Bt-crops were obtained using mathematical models of population genetics . The results were published in the journal Nature Biotechnology .
The results of joint research on the effectiveness of the Chinese method of combating the spread of δ-toxin-resistant pests. The dots indicate plantations, the letters indicate the names of the relevant Chinese provinces. The colors of the dots reflect the prevalence of δ-toxin-resistant pests.
It can be seen that in the period from 2010 to 2013 the situation has worsened, and in some regions is already taking a threatening turn. If, as of 2010, the average number of pests immune to the δ-toxin was slightly less than 1% of their total number, then in 2013 in some regions it already reached 12%. At the same time, by the end of the reporting period, the presence of resistant pests was detected in those areas that were considered free from them in 2010. At the same time, the “safety zones” method used in the USA shows the best results: over the same period, the proportion of resistant pests should have grown to values ​​around 1.1%. True, it is worth noting that the Chinese method is much better than nothing: according to the mathematical model, when growing exclusively Bt-cotton in 2013, the proportion of pests immune to the δ-toxin would be 98%! To make matters worse, pests with dominant resistance genes are increasingly common on Chinese plantations.
Which of these can be concluded? The thoughtless use of genetic engineering can, in a very, very short time, negate all its advantages and farmers will have to return to insecticides. That is why today scientists are actively developing rational methods for conducting agriculture associated with genetic engineering.
Source: https://habr.com/ru/post/370245/
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