Genome-wide mapping of meiotic recombination products generated by hybrid crossing of two Trichoderma reesei wild isolates QM6a and CBS999.97

Meiosis is a specialized cell cycle that generates genetically divergent gametes or the sexual spores in fungi. Genome-wide DNA double-stranded breaks (DSBs) are spontaneously generated during meiotic prophase and then repaired by homologous recombination using two non-sister homologous chromosomes as templates instead of the sister chromatids. Interhomolog recombination ultimately leads to chiasmata which hold homologous chromosomes together until the transition from metaphase I to anaphase I to ensure proper chromosome segregation. The evolutionarily conserved endonuclease Spo11 is responsible for the initiation of the majority of meiotic DSBs in most studied experimental model organisms. The absence of Spo11 usually results in infertility due to abnormal chromosomal alternations, disrupted meiosis, apoptosis or the production of aneuploid gametes and sexual spores. We show that three Trichoderma species (T. reesei, T. atroviride and T. virens) each contains a conserved spo11 gene. Removal of the T. reesei spo11 gene resulted in no apparent defect in the entire sexually developmental process, including the formation of stromata, perithecia, asci and ascospores. To further reveal the molecular mechanism of meiotic recombination in the presence and absence of spo11, we have applied both next- and third-generation sequencing platform to generate high-resolution genetic maps before and after sexual crossing of two T. reesei wild isolates QM6a and CBS999.97. Our results will be useful for applying sexual crossing to industrial strain improvements.