Meiotic Recombination in Neurospora crassa Proceeds by Two Pathways with Extensive Holliday Junction Migration

Abstract

Analysis of thousands of Δmsh-2 octads using our fluorescent recombination system indicates that, as in other filamentous fungi, symmetric heteroduplex is common in the his-3 region of Neurospora crassa. Symmetric heteroduplex arises from Holliday junction migration, and we suggest this mechanism explains the high frequency of His+ spores in heteroallelic crosses in which recombination is initiated cis to the his-3 allele further from the initiator, cog+. In contrast, when recombination is initiated cis to the his-3 allele closer to cog+, His+ spores are mainly a result of synthesis-dependent strand annealing, yielding asymmetric heteroduplex. Loss of Msh-2 function increases measures of allelic recombination in both his-3 and the fluorescent marker gene, indicating that mismatches in asymmetric heteroduplex, as in Saccharomyces cerevisiae, tend to be repaired in the direction of restoration. Furthermore, the presence of substantial numbers of conversion octads in crosses lacking Msh-2 function suggests that the disjunction pathway described in S. cerevisiae is also active in Neurospora, adding to evidence for a universal model for meiotic recombination.

RecombineX: A generalized computational framework for automatic high-throughput gamete genotyping and tetrad-based recombination analysis

“…PMS is important for dissecting the detailed molecular mechanisms of recombination. PMS is directly detectable in filamentous fungi that naturally form octads or after micromanipulation of yeast tetrads [ 11 , 17 , 20 , 21 ]. To allow PMS identification, we added an option that enables RecombineX to report all marker sites with admixed genotype signals.…”

RecombineX: a generalized computational framework for automatic high-throughput gamete genotyping and tetrad-based recombination analysis

“…PMS is important for dissecting the detailed molecular mechanisms of recombination. PMS is directly detectable in filamentous fungi that naturally form octads or after micromanipulation of yeast tetrads (Martini et al 2011; Yeadon et al 2016; Marsolier-Kergoat et al 2018). To allow PMS identification, we added an option that enables RecombineX to report all marker sites with admixed genotype signals.…”

Recombination hotspots inNeurospora crassacontrolled by idiomorphic sequences and meiotic silencing

“…cog is naturally polymorphic, with two codominant alleles (ANGEL et al 1970;YEADON et al 2004) of which cog + stimulates ~25 times more recombination than cog (YEADON et al 2004). When rec-2SL (previously known as rec-2 + ) is present in a cross, recombination is independent of the cog genotype (CATCHESIDE AND ANGEL 1974) and is reduced by up to 100-fold (YEADON et al 2004;YEADON et al 2016).…”

“…When rec-2SL (previously known as rec-2 + ) is present in a cross, recombination is independent of the cog genotype (CATCHESIDE AND ANGEL 1974) and is reduced by up to 100-fold (YEADON et al . 2004; YEADON et al . 2016).…”