LIFE SCIENCE

In the name of “Wei Qing”, do not teach the “degree of defense” of root swelling disease


During the Western Han Dynasty, the famous general Wei Qing pushed the Xiongnu’s defense line to the Yinshan Mountain Range, so that the Xiongnu did not dare to invade the Yellow River Loop. Now, the collaborative team of Zhou Jianmin and Chen Yuhang of the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences has excavated a broad-spectrum anti-rhizomatous gene in wild mustard greens and named it “Weiqing”.

Rhizomatosis can be called the “terminal disease” of cruciferous crops. Dormant rhizoma spores can survive in the soil for up to 20 years, and once the cultivated land is contaminated, it is impossible to continue growing these crops. Every year, the incidence area of rhizomatous disease in China reaches 48 million ~ 60 million mu. “This will not only bring economic losses to farmers, but also bring great pressure to China’s limited arable land.” Zhou Jianmin told China Science News.

The research team not only cloned the gene “Weiqing”, but also elucidated its mechanism of action to contain rhizomatous disease. The study was published June 8 in Cell. A number of reviewers of the journal believe that this is an “impressive” study with broad application prospects.

Field-grown canola. Photo courtesy of Hu Baocheng, researcher of Anhui Academy of Agricultural Sciences

Looking for “Enemy Masters”

Every spring, the rape fields with their golden flowers become a check-in spot for many tourists. However, out of sight, rapeseed is being threatened by the spreading “big head disease”.

In 2016, when Zhou Jianmin attended an academic conference in Sichuan, Huang Yun, a professor at Sichuan Agricultural University who also studies plant diseases, told him: “When oilseed rape infected by rhizomatous bacteria, the root system will grow ‘tumors’, so that the plants cannot absorb nutrients, and the growth is stunted or dies.” ”

China is a big oilseed rape planter, with a total output of about 30% of the world, ranking first in the world. According to data from the National Bureau of Statistics, in 2021, China’s rapeseed planting area exceeded 100 million mu.

However, when communicating with Zhang Chunyu, an expert in rapeseed disease resistance genetics and professor of the College of Plant Science and Technology of Huazhong Agricultural University, Zhou Jianmin learned that the incidence area of rhizomatosis of rapeseed in China reaches about 20 million mu every year. Once the disease occurs, the loss of one mu of rapeseed can reach about 50% or even higher. This is equivalent to a direct economic loss of more than 400 yuan per mu, and the loss of rapeseed alone will cause billions of yuan every year.

To make matters worse, even if a crop dies, its “tumor” releases dormant spores of rhizoma that live in the soil for 20 years and cannot be planted.

In addition to canola, common cruciferous crops such as cabbage, radish, kale, and cauliflower are also threatened by this devastating soil-borne disease.

Unfortunately, Zhou Jianmin told reporters that at present, there is still “basically no cure” for root swelling. Traditional field management is to spread lime, but it only solves the problem temporarily, cannot be cured, and can lead to soil compaction.

Internationally, although scientists have excavated some rhizomatous disease resistance genes from European turnips, and used them to crossbreed crops such as rapeseed and cabbage to achieve rhizomatous disease prevention and control, the field rhizomatous bacteria are mixed and varied, and the disease resistance genes often show strain specificity, and the mechanism research is weak. Zhang’s team has isolated a new variant strain in the field that can disable some of the anti-rhizomatous genes.

Can broad-spectrum new genes be found against new virulent strains?

Zhou Jianmin and his collaborators isolated and identified a gene with high resistance to rhizomatous from more than 200 wild mustard greens collected from abroad, and named it “Weiqing”.

According to reports, this “enemy general” can encode a protein that has never been reported. After the research team introduced it into rape, not only did it show good resistance, but its growth and development were also completely normal. They found that the gene exhibited highly pathogenic strains on existing resistant varieties, indicating that this is a broad-spectrum resistance gene.

Symptoms of enlarged rape roots affected by rhizomatous disease. Photo courtesy of Yang Hui, associate professor of Sichuan Agricultural University

“Wei Qing” defeated the enemy in this way

So, how can “Wei Qing” subdue the enemy?

Zhou Jianmin’s team and Chen Yuhang’s team uncovered the secrets through cell biology, molecular biology, cryo-EM, electrophysiology and other methods.

Unlike most plant pathogens that “steal nutrients” from plant cells, rhizomatous is cunning in that it burrows into plant cells to multiply. What is particularly harmful is that rhizomatous bacteria will set up camp in the “root core” – the middle column, stimulating the expansion of parasitic cells to help them multiply wildly, which is also the cause of the formation of “big head disease” disease. As the disease progresses, the root tissue of the plant is destroyed and cannot absorb nutrients, resulting in slow plant growth or death.

Zhou Jianmin’s team found that “Wei Qing” is not usually expressed, and only when the enemy is found, it is expressed in a special layer of cells called the middle column sheath, which forms a line of defense on the periphery of the middle column to block the invasion of rhizomatous bacteria into the middle column.

The protein encoded by “Weiqing” is localized to the endoplasmic reticulum. Chen Yuhang’s team found that “Weiqing” is a new ion channel that releases calcium ions in the endoplasmic reticulum into the cytoplasm, so as to sound the “alarm” of bacterial invasion in plant cells and open up the defense response.

“The famous general Wei Qing resisted the Xiongnu invasion by using Yin Mountain as a defensive line to prevent the Xiongnu from invading the Hetao Plain. Similarly, the vascular bundle system of nutrient transmission in the column of plants is like the Hetao plain that inherits the farming civilization, and the ‘Weiqing’ protein assembles into the calcium ion channel of the endoplasmic reticulum to play the role of ‘beaco’. Chen Yuhang, co-corresponding author of the paper, explained by analogy.

“When the arrival of the enemy is monitored, calcium ions are released from the endoplasmic reticulum and transmit the ‘military information’ like a beacon being ignited. In this way, calcium signaling activates the plant immune response process, thus forming a line of defense in the outer sheath of the central column against pathogenic bacteria invading the ‘Loop Plain’. He said that this is also the reason why the research group named it “Wei Qing”.

It is reported that this is also the first time that scientists have discovered intracellular calcium ion release channels in plants, which can activate calcium signals and immune responses in response to pathogenic invasion. “It’s an extremely interesting study.” An international reviewer believes that researchers have broken down disciplinary barriers and used genetics, biochemistry, structural biology and physiology to explain the molecular mechanism of the role of anti-rhizomatous genes.

Mechanism of action of WTS. WTS encodes calcium channels localized to the endoplasmic reticulum, which triggers downstream immune responses by mediating calcium release, resists the invasion of rhizomates, and protects the plant vascular system. Photo courtesy of the research team

It makes a lot of use

Since the discovery of rhizomatous in Taiwan and Fujian in the twenties of the twentieth century, the occurrence area of rhizomatosis in China has been increasing. Especially in recent years, with the continuous development of agricultural mechanization, rhizomatous disease has shown a rapid spread trend in China, and the current occurrence area accounts for about 30% of the national cruciferous crop planting area.

In order to verify the reliability of “Weiqing”, Zhou Jianmin’s team used the highly virulent new variant provided by Zhang Chunyu’s team for testing, and found that the new gene could “subdue” the invasion of this variant strain.

At present, around the world, the use of biological breeding to achieve crop disease resistance and high yields is in the ascendant. Zhou Jianmin hopes that in the future, “Weiqing” can be introduced more accurately into cruciferous crops such as rapeseed through biological breeding, providing more choices for China’s disease resistance gene breeding.

According to reports, this study took 7 years before and after, overcoming many problems such as difficulty in gene verification, small protein fragments, and unstable membrane proteins, resulting in difficulty in mechanism analysis. “Just like new energy vehicles, only when we prepare the core technical products can we quickly provide technical support for the industry when the national biological breeding related policies are liberalized.” Zhou Jianmin said.

Zhou Jianmin’s team has long studied the mechanism of plant immunity. From 2019 to 2021, the team worked with Tsinghua University researcher Chai Jijie and other teams to discover plant disease-resistant bodies for the first time in the world and elucidate the core mechanism of their activation of immunity, solving the problems that have plagued the field of plant immunity for more than 20 years. Now, he and his collaborators are focusing on practical agricultural problems such as rapeseed root swelling, rice blast, and kiwifruit canker disease, hoping to help increase agricultural income through basic scientific research. (Source: China Science News Feng Lifei)

Related paper information:https://doi.org/10.1016/j.cell.2023.05.023



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