The international research team, led by scientists at the John Innes Centre in the United Kingdom, investigated a recently discovered group of plant immune receptors. They identified how these proteins recognize invading pathogens and demonstrated that they can be modified to detect multiple fungal threats. The findings could open the door to crops with stronger, more durable disease resistance. “We’ve discovered something that could lead to a potential intervention on what is the worst fungal disease of cereals,” said Professor Mark Banfield, a research group leader at the John Innes Centre and an author of the study, which involved collaborators at Kobe University in Japan.
A Devastating Fungus Threatens the Global Food Supply
The target of the research is Magnaporthe oryzae, the fungus responsible for blast disease. It causes the most serious fungal disease affecting cultivated rice and has also become a major threat to wheat and barley in parts of Asia and Africa. The damage is enormous. Each year, rice blast destroys enough rice to feed approximately 60 million people. As the fungus spreads into additional agricultural regions, developing effective ways to protect crops has become increasingly important for global food security.
The fungus infects plants through a sophisticated biological strategy. It delivers specialized molecules known as effectors into cells in the 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 recognize these foreign molecules and trigger a protective response. One important mechanism involves causing infected cells to die in a controlled, localized area, helping prevent the pathogen from spreading farther through the plant.
Scientists Discover a Hidden Plant Immune Defense
For more than three decades, much of the research into plant immunity has centered on proteins called Nucleotide-binding and leucine-rich receptors (NLRs). These receptors have played a central role in understanding how crops recognize and defend themselves against blast disease and other infections. More recently, scientists have begun investigating another group of immune proteins found in cereal crops, known as tandem kinase proteins (TKPs). Although researchers are still learning how these receptors operate, they appear to offer additional opportunities for strengthening plant defenses. Earlier studies revealed that some TKPs contain a specialized region called a Heavy Metal Associated (HMA) domain.
Similar regions are also found in certain NLR receptors, where they help recognize pathogen effectors and initiate immune responses. This shared feature attracted the attention of Banfield and his colleagues because it suggested that scientists might be able to redesign the receptors to recognize additional fungal threats. “This piqued our interest,” said Professor Banfield. “If we can engineer these integrated HMA domains for new properties by making amino acid protein changes where effectors bind, we can gain what we call novel recognition specificities – and potentially a new frontline for defense of plants against disease.”
Turning Fungal Attack Molecules Into Targets
In the study, published in Science Advances, researchers examined precisely how HMA domains interact with the molecules released by the blast fungus. Using biophysical techniques and crystallography, a method that allows scientists to determine the detailed three-dimensional structure of molecules, the team obtained a high-resolution view of how these plant receptors bind to fungal effectors. The results revealed that HMA domains can function as biological bait. By binding to molecules the fungus uses during infection, these regions help plants recognize the presence of an invading pathogen and activate their defenses. Armed with this structural information, the researchers modified TKP immune receptors so they could recognize two different fungal effectors associated with infections in wheat and barley.
This ability to detect multiple targets, known as dual specificity, is unusual in naturally occurring immune receptors. Demonstrating that it can be introduced through protein engineering suggests a promising way to expand the range of threats that crop immune systems can recognize. The findings also provide a foundation for investigating other recently identified TKPs in different cereal crops. Scientists may eventually be able to design customized immune receptors that detect several fungal effectors simultaneously, potentially making plants more difficult for pathogens to infect.
Engineering Crops With Stronger Disease Resistance
Although the findings are encouraging, the technology remains at an early experimental stage. The researchers conducted their initial tests using protoplasts, individual wheat cells that serve as a simplified model for studying how plant tissues respond. The next step is to determine whether the engineered receptors can provide effective protection in whole plants grown under controlled greenhouse conditions. “Our study indicates that this new class of resistance proteins is amenable for engineering purposes. We now know that the previous tools we used in engineering NLR receptors may also work with this new class,” said Dr. Daniel Yu, the first author of the study.
Understanding exactly how fungal effectors attach to plant immune receptors could also help researchers take advantage of other technologies. Precision breeding and artificial intelligence may provide additional ways to redesign HMA domains, allowing them to recognize pathogen molecules that previously escaped detection. One particularly promising possibility involves combining different types of immune receptors within the same crop. Because NLRs and TKPs appear to activate plant defenses through different mechanisms, using them together could create several layers of protection. This might make it harder for fungi to evolve ways around a plant’s immune system.
Culled from https://www.sciencedaily.com/
