Abstract
During meiosis homologous chromosomes pair, recombine, and synapse, thus ensuring accurate chromosome segregation and the halving of ploidy necessary for gametogenesis. The processes permitting a chromosome to pair only with its homologue are not fully understood, but successful pairing of homologous chromosomes is tightly linked to recombination. In Arabidopsis thaliana, meiotic prophase of rad51, xrcc3, and rad51C mutants appears normal up to the zygotene/pachytene stage, after which the genome fragments, leading to sterility. To better understand the relationship between recombination and chromosome pairing, we have analysed meiotic chromosome pairing in these and in dmc1 mutant lines. Our data show a differing requirement for these proteins in pairing of centromeric regions and chromosome arms. No homologous pairing of mid-arm or distal regions was observed in rad51, xrcc3, and rad51C mutants. However, homologous centromeres do pair in these mutants and we show that this does depend upon recombination, principally on DMC1. This centromere pairing extends well beyond the heterochromatic centromere region and, surprisingly, does not require XRCC3 and RAD51C. In addition to clarifying and bringing the roles of centromeres in meiotic synapsis to the fore, this analysis thus separates the roles in meiotic synapsis of DMC1 and RAD51 and the meiotic RAD51 paralogs, XRCC3 and RAD51C, with respect to different chromosome domains.
Highlights
Sexual reproduction involves the fusion of maternal and paternal gametes and this means that the parental genetic complement must be halved in the process of gametogenesis, to avoid it doubling at each generation
Working with the flowering plant Arabidopsis thaliana, we present here an analysis of the roles of recombination and key recombination proteins in this process, showing the existence of a DMC1-dependent process which stabilises pairing of centromeric regions of homologous chromosomes and that, in contrast, synapsis of chromosome arms requires RAD51 protein and the RAD51 paralogues, RAD51C and XRCC3
In the work presented here we have analysed meiotic chromosome pairing in recombination mutants of Arabidopsis and show a differing requirement for these proteins in pairing of pericentromeric regions and chromosomal arms regions during meiotic prophase
Summary
Sexual reproduction involves the fusion of maternal and paternal gametes and this means that the parental genetic complement must be halved in the process of gametogenesis, to avoid it doubling at each generation This halving of ploidy is carried out by meiosis, the specialised eukaryotic cell division that involves one round of DNA replication followed by two sequential divisions. It is essential that each daughter cell inherits a full complement of the genetic material and in mitosis this is ensured by centromeric cohesion established at the preceeding S-phase This mechanism ensures proper chromosomal segregation during the second meiotic division, recognition and linking of homologous chromosomes at the first meiotic division is mediated in the majority of eukaryotes by recombination during the first meiotic prophase. In this context it is important to note that the structure of centromeric regions differs considerably between species, ranging from 125 bp in Saccharomyces cerevisiae to the Author Summary
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