Arabidopsis RAD51, RAD51C and XRCC3 proteins form a complex and facilitate RAD51 localization on chromosomes for meiotic recombination.

Hang Su,Zhihao Cheng,Jiyue Huang,Juan Lin,Hong Ma,Yingxiang Wang,Gregory P Copenhaver,Wojciech P Pawlowski

doi:10.1371/journal.pgen.1006827

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.

Highlights

Homologous recombination (HR) is important for repairing DNA damage and maintaining genomic stability
Meiotic recombination starts with a set of programmed DNA double-strand breaks (DSBs), catalyzed by the SPO11 endonuclease
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

Summary

Introduction

Homologous recombination (HR) is important for repairing DNA damage and maintaining genomic stability. The resulting DSB ends are processed by the MRE11- RAD50-NBS1 (MRN) protein complexes to generate 30 single-stranded DNA (ssDNA) tails [2,3], which are subsequently protected by replication protein A (RPA) [4]. Functional homologs of the E. coli RecA protein, RAD51 and DMC1 [5,6] bind to the 3’ tails to form nucleoprotein filaments with the help of several proteins identified in multiple species, including Saccharomyces cerevisiae (Rad52 [7], Rad54 [8], Tid1/Rhd54 [9], Rad55Rad57 [10], Swi5-Sfr1 [11] and PCSS complex [12]), Arabidopsis thaliana (RAD51C [13], XRCC3 [14], MND1-HOP2[15] and ATR/ATRIP [16]), and mammals (Mnd1-Hop2 [17] and Brca2-Dss1 [18]). The nucleoprotein filaments facilitate single-end invasion of a non-sister chromatid, resulting in the formation of a recombination intermediate called a D-loop, which is processed to produce either crossovers (COs) or non-crossovers (NCOs) [19]

Methods

Results

Discussion

Conclusion