Differential expression of mating-type genes in Hirsutella sinensis and natural Cordyceps sinensis

Abstract

Ascomycete reproduction is controlled by the mating-type (MAT) locus, and the existence of homothallic and pseudohomothallic reproduction types has been hypothesized based on genetic data obtained for Hirsutella sinensis, the GC-biased Genotype #1 of Ophiocordyceps sinensis. However, the inconsistent occurrence of the matingtype genes of MAT1-1 and MAT1-2 idiomorphs in numerous H. sinensis strains contradicts the genetic-based capability of the fungus to undergo self-fertilization. In addition to the genetic regulation of the mating process, transcriptional regulation also occurs in H. sinensis strains that show differential transcription of the mating genes or that exhibit transcription of the MAT1-2-1 gene with spliced intron II and unspliced intron I that contains stop codons, which is not consistent with the hypotheses of (pseudo)homothallism. These findings suggest that H. sinensis (either monoecious or dioecious) needs a mating partner to achieve sexual outcrossing (physiological heterothallism or hybridization) for the development and maturation of the fruiting body, ascocarps, and ascospores of natural C. sinensis. However, consistent occurrence and transcription of the mating genes of both MAT1-1 and MAT1-2 idiomorphs have been reported in natural C. sinensis, which includes the multiple GC- and AT-biased genotypes of O. sinensis fungi and other co-colonized fungi. The differential occurrence and transcription of the mating-type genes of MAT1-1 and MAT1-2 idiomorphs in Samsoniella hepiali might reciprocally participate in the reproduction processes of O. sinensis and the entire lifecycle of natural C. sinensis.