Two different pathways for initiation ofTrichoderma reeseiRad51-only meiotic recombination

Abstract

≤250 words)Background: Meiotic recombination is mainly, but not exclusively, initiated by Spo11induced double strand breaks (DSBs) in some sexual eukaryotes. DSBs are repaired by one or two RecA-like recombinases (ubiquitous Rad51 and meiosis-specific Dmc1). In yeast and mammals, Dmc1 is superior to Rad51 in tolerating mismatched sequences during highly polymorphic hybrid meiosis. The mechanisms underlying Rad51-only meiotic recombination remain less studied. Results:The Rad51-only filamentous fungus Trichoderma reesei has only one spo11 gene.Removal of spo11 from T. reesei genome does not affect normal sexual development, meiosis or chromosome synapsis, but results in decrease of interhomolog recombination products to 70%, crossover homeostasis and lower genetic interference. Our results also suggest that T.reesei Rad51, like yeast and mammalian Dmc1 (but not Rad51), can tolerate mismatched sequences during meiotic recombination. Moreover, Topoisomerase II might act redundantly (and predominantly) with Spo11 to initiate meiotic recombination. Conclusion:We suggest that T. reesei is an emerging model for studying Spo11-independent and Rad51-only meiosis.

Third-generation sequencing-based mapping and visualization of single nucleotide polymorphism, meiotic recombination, illegitimate mutation and repeat-induced point mutation

“…Local inversions are shown in magenta. A reciprocal translocation between the D and L segments had been demonstrated previously by microarray-based comparative genomic hybridization ( 1 ) and electrophoretic karyotyping and Southern hybridization ( 6 ). D and L represent segmental duplication and loss ( 12 ), respectively, because most 16-spore asci (>90%) generated by sexual crosses between QM6a and CBS999.97( MAT1-1 ) contain four or eight inviable ascospores and an equal number of segmental aneuploid (SAN) ascospores.…”

“…For example, it took our computing server (with 20 GB of RAM) 4–7 days to apply MAFFT alone for aligning the six homologous chromosomes of QM6a, CBS999.97( MAT1-1 ), F A , F B , F C and F D , respectively. Secondly, T. reesei contains ∼2250 AT-rich blocks, each of ≥ 500 bp ( 1 , 6 ). These AT-rich blocks are highly homologous to each other, resulting in many false-positive or non-allelic alignment results.…”

“…We reported previously that, except for the left terminus of chromosome VI, all other chromosomal ends in QM6a, CBS999.97( MAT1-1 ) and CBS999.97( MAT1–2 ) contain 8–13 telomeric repeats (i.e. TTAGGG at 3′-termini and the reverse complement CCCTAA at 5′-termini) ( 1 , 6 ).…”

“…We previously established high-quality, near-complete genome sequences of QM6a ( 1 ), CBS999.97( MAT1-1 ) and CBS999.97( MAT1–2 ) ( 6 ) using the PacBio SMRT platform. A hallmark of these three T. reesei genomes (∼34 Mb in size) is the presence of ∼2250 AT-rich blocks each with length ≥500 base pairs (bp) ( 1 , 6 ). These AT-rich blocks might be evolutionary remnants of repeat-induced point mutation (RIP), a genome defense mechanism against transposable elements (TE) that is conserved in many Pezizomycotina fungi.…”

“…After genotyping by genomic polymerase chain reaction (PCR), we isolated high-quality, high-molecular-weight genomic DNA from four representative F1 progeny (i.e. F A , F B , F C and F D ) and then applied PacBio's SMRT technology to determine high-quality and chromosome-level genome sequences ( 6 ). Here, we further present a highly organized and modular computational framework named TSETA (Third-generation Sequencing to Enable Tetrad Analysis) through which we processed all six TGS-based and near-complete haploid genome sequences.…”