Arabidopsis RAD51, RAD51C and XRCC3 proteins form a complex and facilitate RAD51 localization on chromosomes for meiotic recombination.
PLoS Genet 2017;
13:e1006827. [PMID:
28562599 PMCID:
PMC5470734 DOI:
10.1371/journal.pgen.1006827]
[Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 06/14/2017] [Accepted: 05/17/2017] [Indexed: 11/22/2022] Open
Abstract
Meiotic recombination is required for proper homologous chromosome segregation in plants and other eukaryotes. The eukaryotic RAD51 gene family has seven ancient paralogs with important roles in mitotic and meiotic recombination. Mutations in mammalian RAD51 homologs RAD51C and XRCC3 lead to embryonic lethality. In the model plant Arabidopsis thaliana, RAD51C and XRCC3 homologs are not essential for vegetative development but are each required for somatic and meiotic recombination, but the mechanism of RAD51C and XRCC3 in meiotic recombination is unclear. The non-lethal Arabidopsis rad51c and xrcc3 null mutants provide an opportunity to study their meiotic functions. Here, we show that AtRAD51C and AtXRCC3 are components of the RAD51-dependent meiotic recombination pathway and required for normal AtRAD51 localization on meiotic chromosomes. In addition, AtRAD51C interacts with both AtRAD51 and AtXRCC3 in vitro and in vivo, suggesting that these proteins form a complex (es). Comparison of AtRAD51 foci in meiocytes from atrad51, atrad51c, and atxrcc3 single, double and triple heterozygous mutants further supports an interaction between AtRAD51C and AtXRCC3 that enhances AtRAD51 localization. Moreover, atrad51c-/+atxrcc3-/+ double and atrad51-/+atrad51c-/+atxrcc3-/+ triple heterozygous mutants have defects in meiotic recombination, suggesting the role of the AtRAD51C-AtXRCC3 complex in meiotic recombination is in part AtRAD51-dependent. Together, our results support a model in which direct interactions between the RAD51C-XRCC3 complex and RAD51 facilitate RAD51 localization on meiotic chromosomes and RAD51-dependent meiotic recombination. Finally, we hypothesize that maintenance of RAD51 function facilitated by the RAD51C-XRCC3 complex could be highly conserved in eukaryotes.
Meiotic recombination and sister chromatid cohesion are important for maintaining the association between homologous chromosomes and ensuring their accurate segregation. Meiotic recombination starts with a set of programmed DNA double-strand breaks (DSBs), catalyzed by the SPO11 endonuclease. Processing of DSB ends produces 3′ single-stranded DNA tails, which form nucleoprotein filaments with RAD51 and DMC1, homologs of the prokaryotic RecA protein. The eukaryotic RAD51 gene family has seven ancient paralogs, in addition to RAD51 and DMC1, the other five members in mammals form two complexes: RAD51B-RAD51C-RAD51D- XRCC2 (BCDX2) and RAD51C-XRCC3 (CX3). To date, the molecular mechanism of CX3 in animal meiosis remains largely unknown due to the essential roles of these two proteins in embryo development. In Arabidopsis, RAD51C and XRCC3 are required for meiosis and fertility, but their specific mechanisms are unclear. Here we present strong evidence that Arabidopsis RAD51 forms a protein complex with AtRAD51C-AtXRCC3 in vivo. Our data also support the previous hypothesis that CX3 promotes RAD51-denpendet meiotic recombination by affecting its localization on chromosomes. Given that the RAD51, RAD51C and XRCC3 proteins are highly conserved in plants and vertebrates, the mechanism we present here could be important for the regulation of meiotic recombination in both plants and vertebrate animals.
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