A potential new defense against devastating crop diseases

An international research team led by scientists at the John Innes Centre in the UK investigated a recently discovered group of plant immune receptors. The researchers identified how these proteins recognize invading pathogens and demonstrated that they can be modified to detect more than one fungal threat.

The discovery could eventually support the development of crops with stronger and more durable disease resistance.

Professor Mark Banfield, research group leader at the John Innes Centre and an author of the study, which included collaborators from Japan’s Kobe University, said: “We have discovered what could lead to a potential intervention against the worst fungal diseases of cereals.”

Rice blast fungus threatens global food security

The research focused on Magnaporthe oryzae, the fungus that causes rice blast. Rice blast is the most serious fungal disease affecting cultivated rice and is also a major threat to wheat and barley in parts of Asia and Africa.

Each year, rice blast destroys enough rice to feed approximately 60 million people. As the fungus spreads to new agricultural regions, developing more effective ways to protect crops is becoming increasingly important for global food security.

Magnaporthe oryzae infects plants through sophisticated biological strategies. It delivers specialized molecules, known as effectors, into cells in leaves and stems. These molecules interfere with normal plant functions, allowing the pathogen to establish an infection and promote disease.

Plants, however, have evolved their own defense systems. Specialized immune receptors can detect foreign molecules and activate protective responses. One important defense mechanism involves killing infected cells in controlled local areas, which helps prevent the pathogen from spreading through the plant.

Discovering hidden immune defenses in cereal crops

For more than 30 years, much plant immunity research has focused on nucleotide-binding leucine-rich repeat receptors, commonly known as NLRs. These receptors play a central role in understanding how crops recognize and defend themselves against blast and other infectious diseases.

More recently, scientists have begun investigating another group of immune proteins found in grains called tandem kinase proteins, or TKPs. Although researchers are still learning how these receptors function, they could provide new opportunities to strengthen crop defenses.

Previous studies found that some TKPs contain a specialized region called a heavy metal-associated, or HMA, domain. Similar domains are present in certain NLR receptors, where they help recognize pathogen effectors and trigger an immune response.

This shared feature prompted Banfield and his colleagues to investigate whether the receptors could be redesigned to recognize additional fungal threats.

“This piqued our interest,” Professor Banfield said. “If we can engineer these integrated HMA domains toward new properties by changing the amino acid the effector binds to, we can acquire so-called novel recognition specificities, which could provide a new front line in protecting plants from disease.”

Engineering immune receptors to recognize fungal effectors

In a study published in Science Advances, the researchers examined how the HMA domain interacts with molecules released by the rice blast fungus.

Using biophysical methods and crystallography, which reveal the detailed three-dimensional structures of molecules, the team obtained a high-resolution view of how plant immune receptors bind to fungal effectors.

The results showed that the HMA domain can act as biological bait. It helps plants detect invading pathogens by binding to molecules that fungi use during infection, allowing the plant to activate its defenses.

Using this structural information, the researchers engineered a TKP immune receptor to recognize two different fungal effectors associated with wheat and barley infections.

This ability to detect multiple targets, known as bispecificity, is unusual among naturally occurring immune receptors. Demonstrating that bispecific recognition can be introduced through protein engineering suggests a potential way to expand the range of threats that crop immune systems can detect.

The finding also provides a foundation for studying other TKPs recently identified in grains. In the future, scientists may be able to design customized immune receptors that recognize several fungal effectors at the same time, potentially making crops less vulnerable to disease.

Could engineered receptors create more disease-resistant crops?

Although the results are encouraging, the technology remains at an early experimental stage.

The researchers conducted initial tests using protoplasts, or individual wheat cells, as a simplified model for studying plant immune responses. The next step is to determine whether the engineered receptors can protect whole plants grown under controlled greenhouse conditions.

“Our study shows that this new class of resistance proteins is suitable for engineering purposes. We now know that previous tools we used to engineer NLR receptors may also work with this new class,” said Dr. Daniel Yu, lead author of the study.

Understanding how fungal effectors bind to plant immune receptors could also help researchers use other approaches. Precision breeding and artificial intelligence may provide additional ways to redesign HMA domains so they can recognize pathogen molecules that have previously escaped detection.

Combining NLR and TKP defenses

One promising possibility is to combine different types of immune receptors within the same crop.

NLRs and TKPs appear to activate plant defenses through different mechanisms. Using both types together could create multiple layers of protection, making it more difficult for fungi to evolve ways around the plant immune system.

“These two classes of immune receptors, NLRs and TKPs, are probably activated in different ways,” Professor Banfield said. “This creates the possibility of stronger immunity in the field because we are not putting all our eggs in one basket.”

“Furthermore, in the future we may be able to use techniques to stack genes encoding TKP and NLR against the same disease to create highly resistant crops. It may be more difficult for pathogens to evolve because they activate immunity differently,” he added.

Growing threats to wheat, rice and barley

As blast disease continues to threaten key food crops, farmers and researchers need more effective forms of protection.

Wheat blast was first identified in Brazil in the 1980s and has since spread to parts of Asia and Africa. Although the disease has not been detected in the UK, climate change could eventually create conditions that threaten grain production in northern Europe.

Outbreaks of rice blast in new regions could pose a serious challenge, particularly because the fungus can damage crops that are essential for feeding large populations.

By showing how an understudied class of plant immune receptors can be engineered to recognize multiple fungal threats, the researchers have identified a potential new strategy for protecting future crops.

Further testing is needed to establish whether the modified defenses work effectively throughout whole plants and under agricultural conditions. If successful, combining different immune receptors could eventually help scientists develop wheat, rice and barley varieties with stronger protection against some of the most destructive fungal diseases in agriculture.