ASY1 mediates AtDMC1-dependent interhomolog recombination during meiosis in Arabidopsis

Abstract

ASY1 is an Arabidopsis protein required for synapsis and crossover formation during meiosis. The chronology of meiotic recombination has been investigated in wild type and an asy1 mutant. We observe a delay between the appearance of chromatin-associated AtSPO11-1 foci and DNA double-strand break (DSB) formation, which occurs contemporaneously with chromosome axis formation and transition of ASY1 from chromatin-associated foci to a linear axis-associated signal. DSBs are formed independently of ASY1 in an AtSPO11-1-dependent manner. They are partially restored in Atspo11-1-3 using cisplatin, but their control appears abnormal. Axis morphogenesis is independent of ASY1, but axis structure may be compromised in asy1. Localization of the strand exchange proteins AtRAD51 and AtDMC1 to the chromatin occurs asynchronously shortly after DSB formation, with AtDMC1 localizing in advance of AtRAD51. In wild-type nuclei, both recombinases form numerous foci that persist for ∼12 h before gradually decreasing in number. In asy1, initial localization of AtDMC1 is normal, but declines abruptly such that interhomolog recombination is severely compromised. Limited ASY1-independent, DMC1-dependent interhomolog recombination remains, but appears restricted to subtelomeric sequences where the homologs are fortuitously in proximity. Thus, ASY1 plays a key role in coordinating the activity of the RecA homologs to create a bias in favor of interhomolog recombination.

Great majority of recombination events in Arabidopsis are gene conversion events

“…2 and SI Appendix, Fig. S9) and roughly coincident with the recombination hot spots reported recently (15). Sanger sequencing of PCR products, from unique pairs of primers in the Arabidopsis genome, confirmed that 17 putatively shared loci sampled (eight gene conversions or nine small COs) were indeed shared among different plants.…”

Detection of genomic variations and DNA polymorphisms and impact on analysis of meiotic recombination and genetic mapping

“…This result is surprising because each GC should originate from a SPO11-mediated DSB, regardless of whether the GC is associated with a CO or a NCO. Although DSBs have not been directly measured in Arabidopsis, several groups have used immunolocalization of recombination proteins such as RAD51 and DMC1 to provide indirect estimates of DSBs ranging from 120 to 220 per meiosis (39)(40)(41). Even if every DSB resulted in a GC, the reported levels appear to be much too high.…”

Analysis of Arabidopsis genome-wide variations before and after meiosis and meiotic recombination by resequencing Landsberg erecta and all four products of a single meiosis

“…We detected only ;15 (nine COs + six NCOs) recombination events per meiosis; however, fluorescence immunolocalization studies in Arabidopsis detected about 120 AtRAD51 foci per meiotic cell (Sanchez-Moran et al 2007), suggesting that there are over 100 DBS sites in a single meiosis. It is possible that there are many recombination events, but most are not detected because the sizes of DSB gaps and GC tracts are very small.…”