Plant cell walls form a key defensive barrier against pathogen attack. When a microorganism attacks a plant, the plasma membrane releases oligosaccharide fragments that act as damage-associated molecular patterns (DAMPs), which in turn activate the plant's immune response. However, in some cases, this complex defense mechanism, which depends on these molecular signals, fails to activate.

This is what happens with the fungal pathogen Zymoseptoria tritici and wheat. The new study, published in New Phytologist, reveals how the pathogen regulates cell wall degradation to limit the early release of oligosaccharide fragments capable of activating the plant's immune response.

Molecular mechanism of immune evasion

Researchers characterized the fungal enzyme β-glucanase (ZtGH45), a molecule capable of degrading mixed-linkage β-1,3/1,4-glucans (MLG) in the wheat cell wall. During the early stages of infection, the fungus downregulates the enzyme, thus preventing the release of mixed-linkage glucan fragments. This allows the pathogen to infect and colonize the host without triggering an immune response.

The study, led by researchers Andrea Sánchez Vallet and Antonio Molina and co-directed by Cristian Carrasco-López and Diego Rebaque, reveals that the timing of expression of the fungal enzyme (ZtGH45) is crucial for the development of the disease This molecular process of immune evasion balances damage to host tissues with the prevention of immune activation, ensuring the success of the infection. This finding provides new insights into the molecular mechanisms of immune evasion in fungal pathogens.