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Department of Plant Sciences

Connecting recombination and diversity in plant genomes

Meiosis is a special cell division that generates gametes required for sex. During meiosis, chromosomes undergo deliberate breakage and repair that can produce reciprocal crossovers and increases genetic diversity. However, as homologous chromosomes may also differ in their DNA sequence, these polymorphisms can feedback onto the recombination pathway. Most commonly, interhomolog polymorphism is thought to have a suppressive effect on crossovers. 

To further investigate how polymorphism affects crossovers, we sequenced multiple populations of the model plant Arabidopsis thaliana. Unexpectedly, we observed that crossovers show a positive relationship with sequence diversity in this species. One consequence of sequence polymorphism is that it can cause mismatches in recombining molecules. These polymorphisms can be detected by MutS homolog (MSH) mismatch repair proteins. Therefore, we mapped crossovers in a msh2 mutant (defective in mismatch recognition) using multiple hybrid backgrounds. 

Although total crossover numbers were unchanged in msh2 mutants, recombination was remodelled from the diverse pericentromeres towards the less‐polymorphic sub‐telomeric regions. We also show that juxtaposition of large heterozygous and homozygous regions causes crossover remodelling towards the heterozygous regions in wild type Arabidopsis, but not in msh2 mutants. Finally, immunostaining showed that MSH2 protein accumulates on meiotic chromosomes during prophase I, consistent with MSH2 regulating meiotic recombination. 

Our results reveal an unexpected pro‐crossover role for the mismatch repair factor MSH2 in regions of higher sequence diversity in Arabidopsis. This work is a close collaboration between the groups of Ian Henderson (University of Cambridge) and Piotr Ziolkowski (Adam Mickiewicz University).

Blackwell AR, Dluzewska J, Szymanska-Lejman M, Desjardins S, Tock AJ, Kbiri N, Lambing C, Lawrence EJ, Bieluszewski T, Rowan B, Higgins JD, Ziolkowski PA, Henderson IR. (2020) MSH2 shapes the meiotic crossover landscape in relation to interhomolog polymorphism in Arabidopsis. The EMBO Journal.