The secretory protein COA1 enables Metarhizium robertsii to evade insect immune recognition during cuticle penetration.

The interplay between the insect immune system and entomopathogenic fungi during cuticle penetration is not yet fully understood. Here, we show that a secretory protein COA1 (coat of appressorium 1) from Metarhizium robertsii, an entomopathogenic fungus causing diseases in a wide range of insects, is required to avoid host immune recognition during cuticle penetration. COA1 is highly expressed on the cuticle and translocated to the cell surface, where it directly binds with and masks carbohydrates of the fungal cell wall to avoid provoking the host's intense immune response.