Programmed Cell Death in Is Controlled by the Allorecognition Determinant .

Nonself recognition following cell fusion between genetically distinct individuals of the same species in filamentous fungi often results in a programmed cell death (PCD) reaction, where the heterokaryotic fusion cell is compartmentalized and rapidly killed. The allorecognition process plays a key role as a defense mechanism that restricts genome exploitation, resource plundering, and the spread of deleterious senescence plasmids and mycoviruses. Although a number of incompatibility systems have been described that function in mature hyphae, less is known about the PCD pathways in asexual spores, which represent the main infectious unit in various human and plant fungal pathogens. Here, we report the identification of (), a novel allorecognition gene, controlling PCD in germinating asexual spores of ; is one of the most polymorphic genes in the genomes of wild isolates. The coexpression of two antagonistic and alleles was necessary and sufficient to trigger cell death in fused germlings and in hyphae. Based on analysis of wild populations of and , alleles appeared to be under balancing selection and associated with -species polymorphisms. We shed light on genomic rearrangements that could have led to the emergence of the incompatibility system in and show that belongs to a much larger gene family in fungi. Overall, our work contributes toward a better understanding of allorecognition and PCD in an underexplored developmental stage of filamentous fungi.