Kill two birds with one stone: anti-“cancer” and stable wheat has a play

Wheat stripe rust resistance identification garden, the left is the disease-susceptible wheat, the right is the editing wheat. Courtesy of Northwest A&F University

Wheat infected with stripe rust fungus under natural conditions Courtesy of Northwest A&F University

Stripe rust is known as the “cancer” of wheat, and since the founding of New China, there have been 8 pandemics, and the cumulative loss of wheat after prevention and control is still 13.8 billion kilograms. China’s Ministry of Agriculture and Rural Affairs lists stripe rust as a class of crop diseases.

On July 14, Cell published online the results of the 18-year research of the Plant Immunity Team at Northwest A&F University. For the first time, the team discovered the “real culprit” in wheat that assists in the infection of stripe rust bacteria – disease-susceptibility genes, and used gene editing technology to make wheat less susceptible to the infection of stripe rust bacteria, while maintaining wheat yield without reducing, opening up new ideas and new ways of disease-resistant wheat breeding.

“Upgrade to fight monsters”: lack of resistance to disease genes

Wheat is one of the most widely grown cereal crops in the world, a staple food for more than 2.5 billion people worldwide, and is the most important food crop. However, pests and diseases often cause significant losses in wheat yields, posing a serious threat to food security.

Kang Zhensheng, the corresponding author of the paper and an academician of the Chinese Academy of Engineering, told China Science Daily that as an airborne fungal disease, wheat stripe rust is the number one major biological disaster in wheat, and it occurs in wheat planting areas all over the world. China has always been the most severe area of the disease, general years will lead to 10% to 30% of the loss of production, and even extinction in severe cases.

In 1950, wheat stripe rust was a pandemic in China, causing a yield loss of 41.37% of the total wheat output that year. Therefore, the effective prevention and control of wheat stripe rust is of great strategic significance to ensuring China’s food security.

“Cultivating and planting disease-resistant varieties is the safest and most economical measure to prevent and control stripe rust.” Kang Zhensheng said. Traditionally, disease resistance genes are mainly used to breed varieties, and disease resistance genes mediated strong resistance, but it is easy to be overcome by pathogens, resulting in frequent epidemics of diseases.

Since the 1950s, the main wheat cultivars in China have used disease resistance genes such as Yr1, Yr9, and Yr26 to defeat round after round of bacterial siege, and have made great contributions to ensuring the safe production of wheat in China.

However, with the “upgrading” of pathogens, disease prevention and control is becoming more and more passive, and the number of disease-resistant genes that can be used to “fight monsters” is decreasing.

Wang Xiaojie, corresponding author of the paper and professor at Northwest A&F University, told China Science News that because wheat varieties have been promoted on a large scale for 3 to 5 years in production, the new toxic strains produced by the mutation of pathogens can often break the resistance of the varieties, resulting in frequent epidemics of diseases.

Traditional methods of cultivating a disease-resistant variety take at least 10 years or so. “The loss of variety resistance is significantly faster than the breeding period, so there are fewer and fewer varieties used to effectively cope with wheat stripe rust, and disease resistance resources are increasingly scarce.” Wang Xiaojie said.

How to break through this dilemma? In addition to disease resistance genes, there are also disease-sensing genes that are closely related to pathogenic bacteria. So scientists set their sights on the disease-sensitive genes.

The susceptibility gene is the host gene necessary for the pathogen to infect and cause disease. Compared with disease resistance genes, resistance mediated by disease-inducing gene mutations often has persistent and broad-spectrum characteristics.

“Modifying and editing disease-sensitive genes is an important new way to improve crop resistance.” Kang Zhensheng said that the negative effects brought about by the pluripotency of the disease-inducing gene limit its application, such as the mutation of the disease-inducing gene can lead to the loss of its own physiological function, affecting the growth and development of plants, yield and other traits. “Finding disease-susceptibility genes that can be utilized has always been a key focus and difficulty in plant pathology and crop disease resistance breeding.”

Relay research: lifting the mystery of the sensory gene

Originally, wheat stripe rust fungus is a living nutrient parasitic fungus, which draws nutrients from host cells through a suction device during infection, and secretes toxic effectors to the host wheat, and the effectors achieve infection of host wheat by manipulating the host disease gene or other ways.

Wang Ning, co-first author of the paper and postdoctoral fellow of Northwest A&F University, said: “The susceptibility gene is necessary for the successful infection, colonization and reproduction of pathogenic bacteria, and the analysis of the mechanism of action of the susceptible gene provides a scientific basis for in-depth understanding of the pathogenic nature of the infection of stripe rust bacteria and the development of disease prevention and control strategies.” ”

The team has long been engaged in the application and basic research of sustainable control of wheat stripe rust. Since wheat stripe rust bacteria cannot be artificially cultivated and cannot be genetically transformed, the team started with the interaction between wheat and stripe rust bacteria in order to find the key pathogenic factors and disease-sensing genes of wheat stripe rust bacteria.

This 18-year-long “race” with germs began with Wang Xiaojie’s doctoral dissertation.

In 2004, under the guidance of Kang Zhensheng, Wang Xiaojie began to study the molecular mechanism of interaction between wheat and stripe rust bacteria.

In 2007, during a gene expression experiment after the rusty fungus infected wheat, he found a gene that had never been seen in wheat and named it TaPsIPK1. He found that silencing the gene reduced the susceptibility of wheat stripe rust; Excessive expression of this gene enhances the susceptibility of wheat to stripe rust bacteria and mediates wheat infection with stripe rust.

However, due to the technical level and hardware facilities of that year, Wang Xiaojie during his doctorate period never unveiled the mystery of this gene. However, he firmly believes that there is an important secret behind this gene. This mystery has always haunted Wang Xiaojie’s heart.

Fast forward 11 years, and the doctor of that year is already a doctoral supervisor. Wang Ning became Wang Xiaojie’s disciple.

Wang Xiaojie “took” out the gene that he had been thinking about for the first time, and gave it as a gift to the disciple who opened the door, hoping that she could uncover the “secret of Pandora’s box” and clarify the confusing relationship between this gene and wheat stripe rust.

Design experimental protocols, study the feasibility of experiments, deliberate on each experimental link… Despite the difficulties, the team members embarked on this path of exploration full of unknowns with the perseverance not to give up.

In the end, the team unearthed the world’s first wheat-susceptible gene TaPsIPK1, which encodes cytoplasmic receptor protein kinase, which is used by bacterial toxic proteins.

Working mode diagram of susceptibility genes Courtesy of Northwest A&F University

Tang Chunlei, co-first author of the paper and associate researcher of Northwest A&F University, introduced that the disease-susceptibility gene TaPsIPK1 negatively regulates the basic immunity of wheat, which can be hijacked by toxic proteins secreted by stripe rust bacteria, released from the cytoplasmic membrane into the nucleus, manipulate transcription factors in the nucleus, inhibit the transcription of resistance-related genes, enhance the transcription level of susceptibility genes, amplify the disease-inducing effect mediated by disease-inducing genes, and promote wheat susceptibility.

Ensure stable production: realize the independent control of seed sources

The world’s first wheat stripe rust susceptibility gene was identified, and the team members were very excited. They expect to verify its application potential in wheat.

Fan Xin, the co-first author of the paper and a doctoral student at Northwest A&F University, introduced that they used gene editing technology to accurately knock out the disease-inducing gene, destroying the identification and interaction of toxic proteins and disease-inducing genes.

It is exciting to note that this wheat edited strain achieves long-lasting broad-spectrum resistance to three major epidemic subspecies of Stripe Rust in China, as well as resistance to wheat leaf rust. Field experiments proved that the edited strain of wheat can also maintain major agronomic traits including 1,000 grain weight, plant height, tillering number, etc., that is, to maintain stable yield.

From 2020 to 2021, the stripe rust pandemic in Shaanxi Province, wheat stripe rust susceptible gene-edited strains planted in the field showed high stripe rust resistance.

“Wheat edited strains show high resistance to stripe rust under the premise of maintaining the quality of the main traits of crops, and have good application potential.” This is a disease-sensing gene that can be used to improve wheat disease resistance. Wang Xiaojie said.

Kang Zhensheng pointed out that the discovery of wheat disease-inducing genes is a major breakthrough in the field of interaction between plants and pathogenic bacteria, marking a big step forward in this field in China. This achievement breaks the traditional idea of wheat mainly using disease resistance genes for breeding, enriches the gene types available for disease resistance breeding, opens up new ways of wheat biological breeding, and provides scientific and technological support for modern biological breeding and disease prevention and control in China.

Chen Jianping, an academician of the Chinese Academy of Engineering, commented that the team created a wheat material with broad-spectrum long-lasting resistance by destroying the interaction between the pathogen effector and the wheat disease-sensing gene, showing great application prospects in the field. This research work is both theoretical breakthrough and production application value, and is a landmark achievement in the field of plant pathology and crop disease resistance breeding.

“The seed industry is entering a new stage of highly intersecting and highly integrated multidisciplinary aspects such as biotechnology, information technology, engineering technology, etc., and has gradually become the key area of the new generation of technological revolution, excellent germplasm and genetic resources are the key to the innovation of the seed industry, who first obtained crop genetic resources, cracked the function of genes, who has the right to speak and dominate the seed industry.” Xu Weigang, an academician of the Chinese Academy of Engineering, said that the original major achievements of the plant immunology research team of Northwest A&F University in the identification and utilization of wheat susceptibility genes are a leap-forward breakthrough in realizing the independent control of seed sources and improving the original independent innovation ability of the seed industry, and opening a new chapter in the independent innovation of China’s seed industry. (Source: China Science Daily, Li Chen, Yang Yuan)

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