Fungal Effectors in Biotrophic, Necrotrophic and Hemibiotrophic Pathosystems: A Systematic Review

Fungal phytopathogens are responsible for numerous plant diseases that result in substantial agricultural losses worldwide. To establish successful infections, fungi secrete effector proteins that facilitate host colonisation and nutrient acquisition. This systematic review summarises the mechanisms of action of fungal effectors in biotrophic, necrotrophic and hemibiotrophic pathosystems. A total of 2979 publications were initially identified, while after screening and data extraction 184 studies were included in the analysis. All told, we compiled 222 secreted effector proteins by 50 fungal pathogens. Of these, 38% originated from biotrophic fungi, 36% from hemibiotrophs and 22% from necrotrophs. The predominant mechanism among biotrophic effectors is the suppression of plant immunity (44 effectors), particularly through the inhibition of programmed cell death and pattern‐triggered immunity (PTI) responses. In contrast, necrotrophic fungi rely on 13 effectors that promote host cell death, whereas hemibiotrophs employ a diverse array of effectors, with 20 implicated as enhancing pathogen growth and virulence. In terms of subcellular localisation, 46% of the effectors act in the apoplast and 54% in the host cytoplasm. Apoplastic effectors contribute to fungal cell wall protection and inhibit plant defence‐related enzymes such as proteases and chitinases. Cytoplasmic effectors target intracellular components, modulating defence signalling pathways. Notably, the ascomycete Magnaporthe oryzae has the highest number of functionally characterised effectors, while basidiomycete pathogens remain underexplored in this regard. This review enhances understanding of effector biology in diverse fungal lifestyles and provides a valuable foundation for future research on plant–fungal interactions and disease management strategies.