Together yes, but not coupled: new insights into the roles of RAD51 and DMC1 in plant meiotic recombination

Abstract

. * For correspondence (fax +34 91 394 4844; e-mail pradillo@bio.ucm.es). † E. Sá nchez-Morá n and J.L. Santos acted as joint senior authors. SUMMARYThe eukaryotic recombinases RAD51 and DMC1 are essential for DNA strand-exchange between homologous chromosomes during meiosis. RAD51 is also expressed during mitosis, and mediates homologous recombination (HR) between sister chromatids. It has been suggested that DMC1 might be involved in the switch from intersister chromatid recombination in somatic cells to interhomolog meiotic recombination. At meiosis, the Arabidopsis Atrad51 null mutant fails to synapse and has extensive chromosome fragmentation. The Atdmc1 null mutant is also asynaptic, but in this case chromosome fragmentation is absent. Thus in plants, AtDMC1 appears to be indispensable for interhomolog homologous recombination, whereas AtRAD51 seems to be more involved in intersister recombination. In this work, we have studied a new AtRAD51 knock-down mutant, Atrad51-2, which expresses only a small quantity of RAD51 protein. Atrad51-2 mutant plants are sterile and hypersensitive to DNA double-strand break induction, but their vegetative development is apparently normal. The meiotic phenotype of the mutant consists of partial synapsis, an elevated frequency of univalents, a low incidence of chromosome fragmentation and multivalent chromosome associations. Surprisingly, nonhomologous chromosomes are involved in 51% of bivalents. The depletion of AtDMC1 in the Atrad51-2 background results in the loss of bivalents and in an increase of chromosome fragmentation. Our results suggest that a critical level of AtRAD51 is required to ensure the fidelity of HR during interchromosomal exchanges. Assuming the existence of asymmetrical DNA strand invasion during the initial steps of recombination, we have developed a working model in which the initial step of strand invasion is mediated by AtDMC1, with AtRAD51 required to check the fidelity of this process.

The Absence of the Arabidopsis Chaperone Complex CAF-1 Produces Mitotic Chromosome Abnormalities and Changes in the Expression Profiles of Genes Involved in DNA Repair

“…The exceptions are rad51-2 , a T-DNA insertion line generated in Wassilewskija (Ws) background (Pradillo et al, 2012), and fas2-1 , which has been generated by EMS in Landsberg erecta (L er ) background (Endo et al, 2006). The mutant alleles rad51-3 (SAIL_873_C08) and dmc1-2 (SAIL_170_F08) were obtained from the Salk Institute Genomic Analysis Laboratory (SiGnAL 1 ; Alonso et al, 2003), and provided by the Nottingham Arabidopsis Stock Centre (NASC).…”

OsDMC1 Is Not Required for Homologous Pairing in Rice Meiosis

“…In Osdmc1a Osdmc1b, bouquet formation was similar to that of the wild type, implying that early chromosome alignment does not depend on OsDMC1. Unlike Atdmc1 (Pradillo et al, 2012;Da Ines et al, 2012), mutation of OsDMC1 did not lead to serious pairing defects. In the earlier work, the RNAi to OsDMC1 led to homolog pairing defect (Deng and Wang, 2007).…”

Spatiotemporal Asymmetry of the Meiotic Program Underlies the Predominantly Distal Distribution of Meiotic Crossovers in Barley

“…In Arabidopsis, RAD51 and DMC1 are essential for DSB break repair and CO formation, respectively (Couteau et al, 1999;Li et al, 2004;Kurzbauer et al, 2012;Pradillo et al, 2012). The barley homologs share 92 and 53% amino acid sequence identity with the regions of RAD51 and DMC1 used to make the Arabidopsis Abs, respectively (see Supplemental Figure 1 online).…”