Improving the quality and productivity of crops by modifying their native properties to increase resistance to pests and extreme weather conditions has been going on for ages. Various methods have been used, such as crossbreeding, genetic recombination, and genome editing (which contains all genetic information). But each takes time and effort.
Recently, however, a team from RIKEN and Kyoto University has become the first in the world to effectively control proteins that impact an organism’s characteristics by simply targeting small organs inside cells and by spraying them with nucleic acid.
Conventional modification methods
“Hybridization is one of the methods used to modify characteristics. It involves crossing plants of different species, for example a variety that tastes good with another resistant to pests, to create a new plant that inherits both positive traits. However, it takes several hundred or even several thousand years of breeding to select the characters. Developing a new species in this way is a long process.
Genetic modification brings out certain traits by inserting genes related to the given trait, such as drought resistant genes and genes that produce larger fruits, into the crops genome. But, where the genes end up in the original genome is up to chance, possibly introducing unwanted traits. As such, it is necessary to strictly manage security and species selection, which requires time, effort and high cost.
In recent years, genome editing has also attracted attention. Instead of introducing new genes from outside, traits are changed by cutting and modifying a specific gene in the existing genome using enzyme “scissors”. For example, if there is a gene that limits nutrient production, it can be knocked out to produce more nutritious crops. However, this method also requires effort, cost and a high degree of security.
Produce substances hated by pests
The research team is studying the improvement of pest resistance in soybeans. Bed bugs are the natural enemy of soybeans. They suck juice from bean pods and inhibit growth and quality. Exterminating them with pesticides takes effort and is expensive. Thus, the question is whether it would be possible to induce soy to create substances that bedbugs do not like. If the genetic information that makes these proteins repellent against bedbugs is sent into cells, their resistance to pests can increase.
However, genetic modification and genome editing are fraught with problems and time consuming.
Is there an easier way to edit traits? As a result of repeated studies, the idea of using a substance called “cell-penetrating peptide (CPP)” was developed.
A CPP, which is a series of short chains of amino acids, is able to cross the membrane surrounding plant cells and enter inside. If this is combined with artificial nucleic acids that contain the information necessary to produce the desired proteins, mixed with pure water and pulverized, the plants should be easily modified.
Therefore, an artificial nucleic acid that produces fluorescent proteins that turn green when exposed to ultraviolet light was created and synthesized into nano-sized molecules in combination with CPPs. After mixing it with water, it is sprayed on watercress (an annual herb), soybeans and tobacco, among other plants, which are then exposed to ultraviolet light. When the leaves turn green, it shows that it is possible to synthesize proteins using this method.
Aim for the chloroplast
One problem is that the amount of protein synthesized this way is low. Although artificial nucleic acids have been able to enter cell nuclei, this is not a suitable place to synthesize large amounts of protein. In order to synthesize a sufficient amount to modify the trait, it is necessary to send the proteins to the chloroplast, which is one of the organelles of the cell and where photosynthesis takes place.
This problem has been solved by incorporating an amino acid sequence that has the function of introducing only the target organelle into the CPP. As a result, the team succeeded in mass producing the artificial nucleic acid proteins inside the targeted chloroplasts for the first time in the world.
In addition to synthesizing the proteins, the team was also able to suppress protein production. When a plant genetically engineered to synthesize a fluorescent protein in the chloroplast is then sprayed with an artificial nucleic acid that inhibits the function of that protein, it does not glow even when exposed to ultraviolet light.
Flexible and extensive application
These findings have the potential to significantly advance crop modification. There is no need for genetic modification or genome editing. And depending on the design of artificial nucleic acids and CPPs, it is possible to freely change the proteins to be synthesized, the genes that inhibit certain functions, and the organelles to be targeted.
This will not only make it easier to repel pests, but it can also contribute to the development of vegetables with more health-enhancing substances.
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In addition, if a substance that promotes flowering is produced, the fruiting cycle will be accelerated and the production efficiency will be improved. We can also restrict genes that impede growth, which can eventually create bigger fruit.
Dr. Keiji Numata, professor at Kyoto University and leader of the team, said: “Because you can change the characteristics of plants with just one spray, you can easily apply it to a wide range of fields.
“It will be particularly suitable for pest control on large farms,” continued Dr Numata. “Instead of modifying the gene itself, it’s basically a transient trait, so it’s also very safe. I want to continue the research and put it into practice as soon as possible.
(Read the report in Japanese on this link.)
Author: Juichiro Ito