Genome compartmentalization in a fungal insect pathogen reveals a second mating-type locus on an accessory chromosome.

An accessory chromosome in the fungal insect pathogen Metarhizium acridum carries both MAT1-1 and MAT1-2 idiomorph genes plus the canonical MAT locus, unlike typical effector-rich accessory chromosomes.

• Why it matters: Accessory chromosomes in fungal pathogens are often linked to host interaction, but how they contribute to mating and recombination remains unclear, especially across diverse isolates.
• What they did: A pangenomic analysis used six chromosomal assemblies from M. acridum isolates spanning four continents to map gene content and identify an accessory chromosome enriched for sexual reproduction functions.
• The result: The accessory chromosome’s mating-type gene complement suggests it may facilitate sexual reproduction, potentially even primary homothallism, and could enhance recombination capacity in an otherwise heterothallic species.

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