Reorganization of secreted MEROPS protease repertoires during ectomycorrhizal evolution in basidiomycete fungi

Ectomycorrhizal (ECM) fungi rely on host-derived carbon but also contribute to soil nutrient acquisition. Although reductions in plant cell wall-degrading CAZymes are well established in ECM fungi, lifestyle-associated changes in secreted proteases remain poorly understood. Here, we compared SignalP-positive MEROPS protease repertoires across a strict ecology dataset of 186 basidiomycete genomes representing ECM fungi, white rot fungi, brown rot fungi, and litter saprotrophs. ECM fungi had fewer putative secreted MEROPS proteases than white rot fungi and litter saprotrophs, with lower representation mainly associated with metalloprotease and serine protease families. Family-level analyses identified S08, S09, S33, M28, M35, M36, and M43 as major contributors to lifestyle-associated variation. Secreted MEROPS repertoires also varied among ECM genus or lineage groups. These results suggest that ECM fungi differ from saprotrophic fungi in candidate extracellular protease systems, providing insight into the evolution of fungal nutrient acquisition strategies.