RESUMEN
Cap expansion in agaricoid mushroom species is an important event for sexual reproduction because meiosis occurs in basidia under the cap, and basidiospores can be released by opening the cap. However, molecular mechanisms underlying cap expansion in basidiomycetes remain poorly understood. We aimed to elucidate the molecular mechanisms of cap expansion in basidiomycetes by analyzing the unique cap-expansionless UV mutant #13 (exp2-1) in Coprinopsis cinerea. Linkage analysis and consequent genome sequence analysis revealed that the gene responsible for the mutant phenotypes encodes a putative transcription factor with two C2H2 zinc finger motifs. The mutant that was genome-edited to lack exp2 exhibited an expansionless phenotype. Some of the genes encoding cell wall degradation-related enzymes showed decreased expression during cap expansion and autolysis in the exp2 UV and genome-edited mutant. The exp2 gene is widely conserved in Agaricomycetes, suggesting that Exp2 homologs regulate fruiting body maturation in Agaricomycetes, especially cap expansion in Agaricoid-type mushroom-forming fungi. Therefore, exp2 homologs could be a target for mushroom breeding to maintain shape after harvest for some cultivating mushrooms, presenting a promising avenue for further research in breeding techniques.