Nanjing Agricultural University and Tsinghua University jointly published a Nature paper: the first to reveal the dual-function disease resistance mechanism of plant immune receptor proteins

Sound east strikes west, bait mode, the devil is one foot high, the road is one foot high.

Plant cell membranes recognize receptors as "outposts" to monitor pathogenic bacteria invasion, and by identifying conserved pathogenic agents of pathogenic bacteria, activate plant multi-level defense systems, and generate resistance
to pathogenic bacteria.
Since its first international identification in 1994, plant cell membrane receptor proteins have been the focus of attention as disease resistance receptors, but the mechanism of action for how they are activated to exert resistance has not been revealed
.

Using crystal diffraction and cryo-electron microscopy techniques, the collaborative team resolved the structures that identified a number of different states, such as the "resting state" of the receptor RXEG1, the "intermediate state" of RXEG1-XEG1, and the
"activation state" of RXEG1-XEG1-BAK1.
Through a variety of biochemical and functional analyses, it was determined that XEG1 as a ligand combined with RXEG1 extracellular domains induced conformational changes
in the island region of RXEG1.

The study first clarified the specific mechanism
by which cell membrane receptor proteins perform the function of "immune recognition receptors".
"XEG1 is like a key, when the lock of RXEG1 is opened by the key, XEG1 induces RXEG1 conformational changes, thereby promoting the heterodimerization of RXEG1 and BAK1 and activating plant immune signals," According to Associate Professor Wang Yan, co-author of the paper, XEG1 is not directly involved in the interaction between RXEG1 and the co-receptor protein kinase BAK1, but promotes the interaction of RXEG1 and BAK1 through allosteric effects to activate plant resistance
.

Figure Note: Specific mechanism
by which the cell membrane receptor protein RXEG1 exerts the function of "immune recognition receptor".
After XEG1 binds to RXEG1, it induces RXEG1 conformational changes, promotes heterodimerization of RXEG1 and the receptor protein kinase BAK1, and activates plant immune signaling

The big breakthrough in the study was also the discovery that RXEG1 can perform a dual function
as a "suppressor".
The study revealed that RXEG1 binds to the enzyme activity pocket of XEG1, and RXEG1 inhibits the glycosyl hydrolase activity
of XEG1 after binding to XEG1.

Fig.
Note: Specific mechanism
by which the cell membrane receptor protein RXEG1 exerts the function of "inhibitors".
RXEG1 binds to the enzyme activity pocket of XEG1, and RXEG1 inhibits the glycosyl hydrolase activity of XEG1 after binding to XEG1, thereby reducing the pathogenicity of Phytophrenia

"XEG1 secreted during pathogenic bacterial infestation destroys plant resistance
through glycosyl hydrolase activity.
RXEG1 is like a big pliers that lock in XEG1's destructive ability to plants," Wang Yan said
.

XEG1 mentioned in the study is a conserved class of glycosyl hydrolases widely present in a variety of pathogenic bacteria such as bacteria, fungi and oomycetes, which can be recognized by various plants such as tobacco, soybeans, tomatoes and other plants to induce immune responses
.
Therefore, this research breakthrough has important guiding significance for improving the broad-spectrum and long-lasting disease resistance of crops, and lays a core theoretical foundation
for the development of green new biopesticides.

Picture Note: Soybean root rot seriously threatens the high yield and stable yield of soybeans in China

In recent years, the research of the Nannong Crop Immunization Team has been carried out
around the process of "attack" of Fossils and "resistance" of plants.
In 2017, through the study of XEG1, the team first proposed a new pathogenic concept of pathogenic bacteria "bait mode", and achieved a major theoretical breakthrough in the field of biological interaction; This collaborative study revealed for the first time the "dual immunity" function of plant receptor disease resistance, which also enabled the team to win both Nature and Science in 5 years, and pry a major breakthrough
in the cutting-edge research field of offensive and defensive mechanisms between pathogenic bacteria and crops.

According to the team leader Professor Wang Yuanchao, the crop immunity team of Nanjing Agricultural University is focusing on a bone that was once considered difficult to gnaw - the disaster mechanism
of major crop diseases.
For more than 20 years, team members have worked tirelessly to gradually uncover what kind of complex and sophisticated "arms race"
is staged between plants and pathogens in the microscopic world invisible to the naked eye.

Knowing oneself and knowing the other, never losing a battle, the wisdom of the ancestors was taken by the team as an important starting point
for scientific research ideas.

Correctly identifying the enemy is the first step
to victory in the battle.
Wang Yuanchao made a vivid analogy: "A person's hair can be cut off at any time, but the shape of the nose and mouth is difficult to change, and what we are looking for is the nose and mouth of the pathogen
.
"

The traditional loss of resistance gene resistance of crops is due to the mutation of pathogenic bacteria traits, and the hair that is cut off does not cause much harm to the pathogenic bacteria, but it can already help the pathogens evade the disease resistance identification
of crops.
What they're doing is finding other ways to find the key characteristic molecules
of relatively stable, pathogenic bacteria.

In 2006, with the completion of the international Phytophthora genome sequencing, Wang Yuanchao realized that he could start from the genome of Phytophthora and follow the vine to find the "nose and mouth" of Phytophthora and study what kind of "weapon" it uses to attack
the plant.

XEG1 is a prevalent, non-variable key factor in different pathogens
.
In 2015, the team first discovered that the glycosyl hydrolase XEG1, secreted by Phytophthora soybean, destroyed the disease resistance of plants by degrading the cell wall by infecting soybeans, and suddenly grasped the "key point"
of the enemy army.

The team's further study found that plant secretion inhibitor protein GIP1 binds to XEG1 and inhibits its enzyme activity to interfere with the role of
XEG1 in promoting fossils infection.
In the process of evolution, Phytophthora obtained the enzymatic live-loss mutant XLP1 of XEG1, used XLP1 as a "molecular bait" to competitively bind GIP1 to protect the core pathogenic factor XEG1 from the attack of plant GIP1, revealing a new pathogenic mechanism of pathogenic bacteria "bait mode"
.

The study then found that XEG1 was degraded by the aspartate protease GmAP5 secreted by the host soybean, and that the pathogen protected XEG1 from the plant extracellular protease GmAP5 through N-glycosylation modification, which further demonstrated that XEG1 is the core pathogenic factor of Phytophthora and that the pathogen needs to be protected
in multiple ways.

For this research breakthrough, Nature reviewers commented: "This is a groundbreaking work in the field of plant immunity, a very exciting discovery.
.
.
.
"
。 This new achievement has two important discoveries: one is the first time to resolve the activation mechanism of plant immune receptor proteins from the atomic level, which greatly promotes people's understanding of plant immune mechanisms, and the other is to find for the first time that receptor proteins have the dual functions
of immune recognition and inhibitors.

The analysis of the activation mechanism of the receptor-like protein RXEG1 provides important clues for improving the broad-spectrum disease resistance of crops in the future, and also provides a theoretical basis
for screening plant immune activators and developing green biopesticides with receptor proteins as molecular targets.

"Through the methods and means of artificial intelligence, it will be possible
to screen a large number of compounds for targeted XEG1 inhibitors and RXEG1-targeting plant immune activators in the future.
" Wang Yuanchao said
.