Powdery Mildew Outsmarts Wheat by Masking Key Effector Signal

Cereals are among the world’s most important staple foods, with wheat alone supplying about 20% of global protein and calorie intake. However, wheat production is increasingly threatened by plant diseases, including wheat powdery mildew. A more sustainable alternative to fungicides is to grow wheat varieties with genetic resistance to the pathogen, but this strategy often loses effectiveness over time because powdery mildew evolves rapidly and can overcome resistance. To better harness natural resistance, a team from the University of Zurich’s Department of Plant and Microbial Biology investigated how the fungus is able to infect wheat even when resistance genes are present.

Their work uncovered a previously unknown interaction between wheat resistance factors and powdery mildew disease factors. “This deeper understanding allows us to deploy resistance genes in a more targeted way and prevents or slows down the breakdown of resistance,” says postdoctoral researcher Zoe Bernasconi, one of the lead authors of the study, which has just been published in Nature Plants.

Wheat is tricked by the fungus in two ways. The powdery mildew fungus produces hundreds of tiny proteins known as effectors. Delivered into host plant cells, these molecules help the pathogen establish infection. In wheat, certain resistance proteins can detect specific effectors and trigger an immune response that halts disease. The fungus often escapes this defense by altering the effectors that are recognized or by losing them altogether.

In this study, the researchers identified a previously unknown powdery mildew effector, AvrPm4, which is detected by the well-known wheat resistance protein Pm4. Surprisingly, however, the fungus can still bypass Pm4-based resistance without changing or discarding AvrPm4. Instead, it relies on a second effector that blocks AvrPm4 from being recognized. This second effector, which the researchers have named AvrPm4-suppressor, masks AvrPm4 from the Pm4 resistance protein.

Despite this masking, the suppressor itself is detectable by another wheat resistance gene. This dual-layered strategy employed by the fungus allows it to evade detection by the plant’s immune system, but the researchers have found that stacking both resistance genes could trap the pathogen and improve durable, low-fungicide wheat protection.

The discovery of this interaction between wheat resistance factors and powdery mildew disease factors opens up new avenues for developing more effective and sustainable strategies to combat the fungus. By understanding how the pathogen evades resistance, researchers can design crops that are better equipped to defend themselves against the evolving threat of powdery mildew.

In the long term, this research could lead to the development of wheat varieties that are resistant to powdery mildew without relying on fungicides, reducing the environmental impact of agriculture and ensuring a stable food supply for the growing global population. The ability to stack resistance genes offers a promising solution to the challenge of pathogen resistance evolution, paving the way for more resilient and productive crop systems.

The University of Zurich team’s findings highlight the complexity of the interactions between plants and their pathogens, emphasizing the need for a deeper understanding of these relationships to develop effective and sustainable agricultural practices. As climate change and population growth put increasing pressure on food systems, the ability to protect crops from diseases like powdery mildew is more critical than ever. This research represents a significant step forward in the quest to safeguard global food security.