A team of researchers from the United States and Germany has identified a peptide that increases barley’s susceptibility to a damaging disease known as leaf blotch. This disease, caused by a necrotrophic fungus, uses the peptide to activate an immune receptor in the plant, ultimately killing its cells.
Barley, one of the world’s most important crops, is crucial for animal feed, with 155 million tons produced annually. Like many crops, it faces threats from pathogens that can lead to significant yield losses. Spot blotch, a disease caused by a fungus that kills infected plant cells, is one of the most destructive barley diseases. It causes dark, chocolate-colored blotches on leaves, leading to dry, damaged foliage.
In the 1990s, a new strain of spot blotch emerged in North Dakota, the heart of U.S. barley production. Some barley plants were highly susceptible to the strain, while others seemed resistant. To pinpoint the gene responsible for this vulnerability, Shaobin Zhong’s team at North Dakota State University induced random mutations in barley seeds. Their research revealed that mutations in a gene called **Scs6** were responsible for the plants’ susceptibility. When this gene was transferred to resistant barley varieties, those plants became highly vulnerable to the disease.
Thirty years after the spot blotch strain first caused damage, the gene behind this susceptibility was identified. However, researchers were puzzled when they found that **Scs6** belonged to the MLA family of immune receptors, which are typically responsible for defending against biotrophic pathogens, or those that require living plant hosts. This raised the question: why would a receptor that typically helps the plant fight off pathogens be involved in making it more susceptible to spot blotch?
To solve this, Zhong’s team collaborated with researchers led by Paul Schulze-Lefert at the Max Planck Institute for Plant Breeding Research in Germany. Their experiments, led by graduate student Florian Kümmel, aimed to understand how the immune receptor could make barley plants more vulnerable to infection.
The research team previously discovered that a non-ribosomal peptide plays a key role in the virulence of barley spot blotch. They hypothesized that this unusual peptide activates the **Scs6** receptor, triggering a cell death response that is typically meant to protect the plant from biotrophic pathogens. When extracts from infected barley leaves were applied to healthy barley plants with the **Scs6** gene, they observed the same cell death response. This suggested that the peptide directly interacts with **Scs6**, causing the plant to inadvertently turn its own defense mechanisms against itself.
The findings highlight a potential downside of breeding barley for disease resistance. Over the years, barley domestication and selective breeding have enriched varieties with immune receptor genes like **Scs6**, which are meant to protect plants from specific pathogens. However, this new research suggests that this could inadvertently make plants more vulnerable to other pathogens, such as the fungus responsible for spot blotch.
As co-first author Kümmel explains, “Evolution has seemingly led some pathogens to hijack host immune receptors, turning the plants’ weapons against themselves to make them more susceptible to disease.” This study underscores the importance of careful breeding strategies to ensure that crops are not only resistant to one disease but also protected from other potential threats.
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