Meiotic recombination rate in <i>rfc1-2</i> and a revised model for RFC1 in meiotic recombination.

<p>A. Estimation of the recombination rate in wild type and <i>rfc1-2</i>. Curves in graphs indicate the distribution of meiotic recombination frequency on <i>Arabidopsis</i> chromosome 2 and 3 <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003039#pgen.1003039-Giraut1" target="_blank">[38]</a>. Markers with red (R), cyan (C) and yellow (Y) fluorescence are located on the corresponding chromosome positions. The recombination rates in wild type and mutant are shown in the table below. The same trend was obtained from two independent biological replicates. NOR, Nucleolar organizer region; Chr, chromosome. Block box represents the centromere. B. A revised model for RFC1 function in type I CO formation during meiotic recombination. As shown in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003039#pgen-1003039-g001" target="_blank">Figure 1A</a> or original DSBR model <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003039#pgen.1003039-Szostak1" target="_blank">[3]</a>, NCOs and COs are proposed to require leading strand DNA synthesis. However, formation of dHJ requires the capture of the second ssDNA end and the stabilization and extension, respectively, of the DNA heteroduplex with the help of the MSH4/5 complex and MER3. In the revised model, we hypothesize that the Type I pathway needs the RFC1-dependent lagging strand DNA synthesis (green dotted arrow) during D-loop extension, which occurs simultaneously with leading strand synthesis (red dotted arrows) that uses the 3′ invading end as the primer, consistent with a DNA replication mechanism in eukaryotes and supported by this study. C. A possible mechanism for the formation of multivalents in <i>rfc1-2</i>. RFC1 is required for dHJ formation between homologs. In the absence of RFC1, MUS81-dependent Type II COs are formed between homolog and non-homologs, resulting in the formation of multivalents.