Liu Xi is in the field, checking the rice varieties. The picture is provided by myself.
Where there is attack, there is defense. The war in the plant kingdom is the same as the war in human beings. Rice has accumulated rich combat experience in the evolution of hundreds of millions of years. How does it stimulate the immune system to start fighting? Who is the sentry in the face of the heavy pressure of rice blast fungus? How did they transmit military information to resist aggression after discovering the enemy’s situation? What tactics does rice use to fight?
After eight years of in-depth research, the team of Academician Wan Jianmin of Nanjing Agricultural University successfully cloned a new gene OsCNGC9 for regulating innate immunity of rice by methods of mutant identification, genetic analysis and gene mapping, revealing the molecular mechanism of the gene affecting rice blast resistance at seedling stage, discovering the inherent nature of rice relying on calcium channels to stimulate its own immune system to resist rice blast, and unveiling the mystery of rice war against rice blast. A few days ago, related research results were published online in the international authoritative academic journal Cell Research.
The beauty expert chose an ugly guy.
Liu Xi, an associate researcher at Nanjing Agricultural University, frowned when he saw brown necrotic spots on eight rice leaves, just like senile spots. As a breeding expert, he is in a beauty contest, and he likes the beautiful rice with "green stems and yellow seeds". These plants must be eliminated.
He didn’t expect that these eight diseased seedlings infected with rice blast, like those wild rice plants discovered by Yuan Longping, would become his most important scientific discovery at present, which opened a new milestone in the field of rice research.
It was a day in March, 2011, and he reviewed his more than 100,000 soldiers at Hainan Breeding Base — — More than 100,000 rice plants were heading at that time. Like a farmer, Liu Xi’s face is tanned. In order to speed up the breeding progress, like a migratory bird, he cultivates rice in Hainan in winter and Nanjing in summer.
Liu Xi planted more than 10 mu of rice in Hainan. There are too many rice materials, including 3,000 or 4,000 different kinds of breeding materials, and one material grows 40 seedlings. Every day, he has to observe, take photos and record in the field. He remembers the name, number and appearance of each rice plant, and he visits each rice plant at least four times a month.
These eight plants are nothing, and only a few varieties of three or four thousand rice seeds can be selected and propagated in the end.
A few days later, he saw these eight ugly guys again. "Age spots" are spreading, and their growth is also very poor, and they are a little short. He decided to wait a little longer to see.
A month later, although the "age spots" of these eight ugly guys continued to expand, they did not die, but they also bore fruit like other normal rice, although they were slightly thin.
What makes these eight rice plants look so ugly? Looking at the handsome companions next to the ugly guy, Liu Xi fell into deep thought and began to pay attention to them. When the harvest came, he harvested these eight ugly guys alone and took them back to Nanjing to continue planting.
Growing this generation in Nanjing, the ugly guy is not obvious. Liu Xi didn’t lose heart. It seems that this guy is a recessive gene control like a single eyelid. He decided to keep planting and see what the ugly guy was like.
It has been planted for two generations in a row. After continuous self-homozygosity, the ugly guy’s "ugly appearance" has finally been stably inherited, and features such as "senile plaque" have appeared continuously. Like the first generation, although ugly, they can all survive and breed offspring.
At the beginning of 2013, Liu Xi reported it to Academician Wan Jianmin as a new mutant material. Academician Wan Jianmin decided to start the research as a project.
Determining the identity of disease-resistant heroes by gene mapping
This project was given to Wang Jiachang, a 23-year-old young man, who was studying for a master’s degree at Nanjing Agricultural University. Professor Wang Yihua, the instructor, told him that it is no problem to graduate from this project, but what kind of discovery you can make depends on yourself.
Wang Jiachang didn’t expect this project to produce great results. His plan at that time was that as long as the doctor could graduate smoothly and find a good job.
After getting this special rice material, Wang Jiachang began to analyze it in detail by means of genetics and molecular biology.
Judging from the performance of field growth, the ugly guy began to become ugly after heading of rice — — When I was a child, ugly guys were not ugly, just like normal rice.
Through genetic analysis, Liu Xi found that 1/4 of the second generation of cross between ugly guy and normal companion had the phenotype of ugly guy. According to Mendel’s genetic law, it is a recessive gene that controls the ugliness of ugly guys, which is the same as Liu Xi’s previous guess.
Do genetic mapping first. Wang Jiachang and Liu Xi compared the ugly guy’s 12 chromosomes with normal varieties and screened them one by one to see which gene had a mutation.
Scientific research is very boring. There are more than 30,000 genes in rice. According to the house number of chromosome — — Molecular markers, finally found a different chromosome fragment on the ninth chromosome.
After getting this clip, the two began to go to the house to search for the hidden murderer who caused the ugly guy to be "ugly".
They used biochemical methods to analyze and found that a normal gene that turned out to be an ugly guy was seriously damaged and lost its function! According to the characteristics of this normal gene and the naming rules of biology, they gave this gene a name — — OsCNGC9 (A Jiu for short).
In organisms, the ion channel is like a city gate, which is guarded by a special person. All kinds of ions can go where they want to go through a special channel. They found that calcium ions prefer to walk the gate guarded by A Jiu.
Wang Jiachang is a little confused: What is the relationship between calcium ion, A Jiu and ugly guys’ "ugliness"? Which direction should we study? He began to consult all kinds of documents. In two years, he has been groping: what affects the fertility of rice? Or caused the aging of rice? It may also affect its plant height traits? What is the relationship between phenotypic traits such as "senile plaque", short stature and few offspring?
Two years later, several research directions of concern have not achieved good results, and Wang Jiachang is very anxious. In the second half of 2015, when he read the literature, he found that a large number of calcium ions would transmit defense information to cells during plant disease resistance, and calcium ions were recognized as the second messenger (the first messenger was plant hormone — — However, scientists in the field of plant disease resistance have always been curious about which channel the "communication soldier" calcium ion came in from.
The "senile plaque" on this ugly guy is the performance feature of many important immune genes. Did A Jiu affect the information transmission? Is it guarding the calcium channel?
Rice blast is a cancer of rice. The attacked rice suffered heavy casualties, ranging from 20% reduction in yield to no grain harvest. According to the data of the Ministry of Agriculture, in recent years, rice blast has caused more than 3 billion kilograms of food losses to China every year, and the annual loss of food in the world can feed 60 million people for one year.
When he put forward the research direction of rice blast, Academician Wan, the tutor, was very interested and gave him some suggestions to support him to continue his research. Combined with years of field observation, Liu Xi also supports this direction.
Wang Jiachang first analyzed whether A Jiu has resistance to rice blast. In order to avoid the influence of other factors such as "senile plaque" on the resistance analysis of rice blast, they chose to analyze the resistance of ugly guy who has not become ugly, and found that his disease resistance is very poor, his immunity is low, and A Jiu is closely related to calcium ions.
Heroic feats of disease-resistant heroes
What needs to be studied is: Is the "city gate" on duty in A Jiu a dedicated channel for calcium ions? To confirm this conclusion, electrophysiological experiments need to be carried out in animal cells. An interdisciplinary research problem is in front of them. Wang Jiachang has been studying plants and suddenly turned to the field of zoology, feeling blind.
At this time, the Institute of Plant Physiology and Ecology, Shanghai Institute of Life Sciences, Chinese Academy of Sciences, provided him with help to transform A Jiu into human embryonic kidney cells: if A Jiu is on duty for calcium channels, there will be obvious current formed by calcium ions after applying voltage inside and outside the cells.
As expected, when the voltage is applied to -200 mV, the current reaches -100 pA, which confirms that A Jiu is a dedicated channel for calcium ions.
In the process of plant disease resistance, does calcium also take this channel? After a series of physiological and biochemical experiments, it was found that because of A Jiu’s "sacrifice", no one opened the city gate, the calcium ion channel lost its function, and the calcium ion of the "communication soldier" could not enter the city to transmit military intelligence, which led to the lax defense in the city and no one took up the battle. The researchers found that other immune indexes of ugly guy were lower than those of normal rice. This shows that A Jiu is the "intelligence officer" who is on duty for the special military intelligence channel, and they give it a formal name — — Cyclic nucleotide ion channel 9.
At this time, another question appeared in their minds. The calcium ion of the "communication soldier" entered the city to transmit military intelligence. Who reported to the "intelligence officer" A Jiu to let the calcium ion of the "communication soldier" enter the city smoothly and set off an alarm to start the immune response? Through a series of biochemical experiments, they found another gene OsRLCK185 (referred to as "Awu") which regulates disease resistance. When "Awu" the sentry found the signal of foreign invasion, he quickly reported it to "intelligence officer" A Jiu, and A Jiu opened the "city gate" to allow "communication soldier" calcium ions to assemble in cells, so that the rice center started an immune response and enhanced rice disease resistance.
A battle process gradually formed in the minds of researchers. A Jiu, the "intelligence officer", played a vital role in the battle between rice and Magnaporthe grisea. Academician Wan Jianmin, the correspondent of the article, gave a vivid metaphor to the reporter. This series of processes is like an "offensive and defensive battle". Previously, researchers only saw the "communication soldiers" and knew little about how the previous "intelligence officers" and "sentries" played their roles.
This experiment has opened up a new research field, and discovered the calcium channel through the new gene, which is an immune signal transmission path from pathogen identification to calcium channel activation, and revealed the role of the new gene (OsCNGC9) in calcium ion elevation and rice disease resistance, providing important materials and theoretical basis for rice rice rice breeding against rice blast.
In order to study whether A Jiu, a hero of disease resistance, has the potential to improve rice blast resistance. The researchers used transgenic methods to verify it. A Jiu, a hero of disease resistance, was transferred to normal rice varieties to observe the change of disease resistance.
"In fact, it is to add more disease-resistant genes to rice cells, which is equivalent to adding several special military intelligence transmission channels." Wang Jiachang explained.
The next step is to continue the differentiation of cells containing new genes, cultivate rice seedlings, inoculate rice seedlings with Magnaporthe grisea and observe its growth and changes. The experiment was successful, and the new gene can significantly improve the disease resistance of rice, and the statistical analysis of the data is very significant.
Professor Ling Chiang, the assistant of Academician Wan Jianmin, said that this project is interdisciplinary and cross-platform, and has been supported by the Institute of Crop Science of Chinese Academy of Agricultural Sciences, the Institute of Plant Physiology and Ecology of Shanghai Institute of Life Sciences of Chinese Academy of Sciences, and the Institute of Genetics and Developmental Biology of Chinese Academy of Sciences.
The scientific community pays close attention to the research results of "calcium channel". Wan Jianmin believes that this achievement provides an important material and theoretical basis for rice blast resistance breeding.
Dr. Wang Jiachang, the co-first author of the article and Nanjing Agricultural University, told the reporter that he would continue to study the function of calcium channels in plants. "This project has changed my life plan." (China Youth Daily China Youth Network reporter Li Runwen correspondent Xu Tianying)
