Photo Credit: Wolfgang Hasselmann
Scientific Frontline: "At a Glance" Summary
- Main Discovery: Researchers at the University of Zurich identified a novel immune evasion strategy in wheat powdery mildew (Blumeria graminis), where the fungus employs a secondary effector protein specifically to mask the presence of a primary effector (AvrPm4) from the host's immune system.
- Biological Mechanism: Unlike typical resistance evasion—where pathogens mutate or discard detected proteins—this mechanism allows the fungus to retain the vital AvrPm4 effector by deploying a second "masking" effector that blocks recognition by the wheat resistance protein Pm4.
- Critical Interaction: The secondary masking effector exhibits a dual function; while it inhibits Pm4-mediated detection, it is simultaneously vulnerable to recognition by a separate, distinct wheat resistance protein, creating a potential "evolutionary trap."
- Experimental Application: Laboratory trials demonstrated that "stacking" the resistance gene for Pm4 with the gene targeting the secondary effector successfully neutralizes the pathogen, as the fungus cannot suppress one immune response without triggering the other.
- Significance: Published in Nature Plants (January 2026), this finding offers a blueprint for engineering durable wheat varieties that exploit interacting fungal effectors to significantly delay or prevent the "breakdown" of disease resistance in global agriculture.
Cereals have natural resistance to pathogenic fungi, but powdery mildew, for example, can overcome this resistance. A team at the University of Zurich has now discovered a new mechanism that enables powdery mildew to outsmart the immune system of wheat. This opens the door to targeted development of resistant varieties with a reduced risk of resistance breakthrough.
Cereals are among the most important staple foods. Wheat alone provides around 20 percent of the supply of protein and calories to people around the globe. However, its production is threatened by plant diseases such as the wheat powdery mildew fungus. One sustainable alternative to using fungicides is to grow varieties of wheat that are genetically resistant to this pathogen. However, in many cases this is not effective in the long term because powdery mildew quickly evolves and is able to overcome any resistance.
Exploiting natural resistance
A team from the Department of Plant and Microbial Biology at the University of Zurich has now conducted more in-depth studies to establish how the fungus is able to infect the wheat despite the presence of resistance genes. The researchers discovered a previously unknown interplay between resistance factors in wheat and disease factors in powdery mildew. “This deeper understanding makes it possible to deploy resistance genes in a more targeted way and prevent or slow down the breakdown in resistance,” says postdoctoral researcher Zoe Bernasconi, one of the lead authors of the study, which has just been published in Nature Plants.
The powdery mildew fungus produces hundreds of tiny proteins, known as effectors, which it introduces into the cells of the host. This is where they help establish an infection. Resistance proteins produced by wheat can recognize some of these effectors directly. This triggers an immune response that stops the infection. However, the fungus frequently gets around this by modifying recognized effectors or even losing them entirely.
Wheat is tricked by the fungus in two ways
The research team has now identified a novel powdery mildew effector (called AvrPm4) that is recognized by the known wheat resistance protein Pm4. Yet surprisingly, the fungus can overcome the Pm4-mediated resistance − and can do so without modifying or losing the effector. Its clever trick is that it has a second effector that prevents the recognition of AvrPm4. “We suspect that the function of AvrPm4 is vital for the fungus to survive, and that’s why this unusual mechanism has developed over the course of its evolution,” says Bernasconi.
What’s particularly exciting is that the second effector has a dual function. It not only prevents the recognition of the first effector AvrPm4 but is also recognized by another resistance protein itself. “This means that, by combining the two resistance proteins in the same variety of wheat, it might be possible to lure the fungus down an evolutionary dead end in which it can no longer escape the immune response of wheat,” says postdoctoral researcher Lukas Kunz, another lead author of the study.
New approaches to produce resistant wheat varieties
“Because we now know these mechanisms and the pathogenic factors of the fungus involved, we can take more effective action to prevent powdery mildew from breaking through wheat’s resistance,” says Beat Keller, the professor who led the research group until he retired last year. By monitoring the powdery mildew pathogen, it would now be conceivable, for example, to use resistant wheat varieties in a targeted manner in places where they will have maximum impact.
A clever combination of resistance genes in new varieties of wheat would also be an option. “Theoretically, measures like these could significantly slow down the development of new pathogenic fungal strains,” says Keller. The team has already conducted the first few promising experiments in the laboratory. To do this, they combined resistance genes that switched off both the AvrPm4 effector and the second effector. But whether this approach will be shown to work in the field remains to be seen.
Published in journal: Nature Plants
Authors: Zoe Bernasconi, Aline G. Herger, Maria Del Pilar Caro, Lukas Kunz, Marion C. Müller, Ursin Stirnemann, Megan A. Outram, Victoria Widrig, Matthias Neidhart, Jonatan Isaksson, Seraina Schudel, Sebastian Rösli, Thomas Wicker, Kyle W. Bender, Cyril Zipfel, Peter N. Dodds, Melania Figueroa, Javier Sánchez-Martín, and Beat Keller
Source/Credit: University of Zurich
Reference Number: bot011226_01
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