A pathogen effector FOLD diversified in symbiotic fungi

Area of Science:

• Mycology
• Plant-Pathogen Interactions
• Symbiotic Fungi

Background:

• Pathogenic fungi secrete effector proteins to suppress host immunity.
• Effectors are also found in symbiotic fungi, like arbuscular mycorrhizal (AM) fungi, which form nutritional symbioses with plants.
• Sequence-based comparisons of effectors between pathogens and AM fungi are challenging due to high sequence diversity.

Purpose of the Study:

• To identify sequence-divergent but structurally similar effector proteins shared between symbiotic and pathogenic fungi.
• To investigate the role of dual domain (FOLD) proteins in fungal-plant interactions.

Main Methods:

• Compared secreted protein structure models of the AM fungus Rhizophagus irregularis with known pathogen effectors.
• Utilized structural similarity searches to identify conserved effector families.
• Analyzed gene family expansion, diversification, and positive selection in AM fungal FOLD genes (MycFOLDs).
• Examined MycFOLD gene expression patterns during plant colonization.

Main Results:

• Identified MycFOLD proteins in AM fungi structurally similar to pathogen FOLD effectors.
• MycFOLD genes are present in expanded and diversified families in AM fungi, with evidence of positive selection.
• Structural modeling suggests MycFOLDs possess carbohydrate-binding motifs.
• MycFOLD genes exhibit differential expression during host colonization, with MycFOLD-17 accumulating in plant arbuscules.

Conclusions:

• MycFOLD proteins are widely distributed across unrelated plant-colonizing fungi, suggesting a conserved function.
• Inducible expression, sequence diversification, and localization in arbuscules indicate MycFOLDs function as effectors in both symbiotic and pathogenic plant colonization.
• FOLD proteins represent a conserved class of fungal effectors involved in plant interactions.