The neddylation pathway regulates the localization of meiotic CO, the pairing of homologous chromosomes and the level of DNA methylation in Arabidopsis thaliana
Résumé
Meiotic crossovers (COs) are important for reshuffling genetic information between
homologous chromosomes and, are essential for their correct segregation. In all species studied,
CO distribution along chromosomes is not homogeneous. The origin of such heterogeneity is
still poorly understood but several lines of evidence point towards chromatin structure and
chromosome dynamics issues (Mézard et al., 2015). We previously demonstrated that the
neddylation/rubylation pathway of protein modification was a key regulator of the localization
of meiotic COs in A. thaliana (Tagliaro-Jahns et al., 2014). In the axr1-/- mutant (the gene
encoding the E1 enzyme of the neddylation complex), COs are mislocalized on chromosomes
but their number is unaffected. We could show that, in axr1, COs were massively redistributed
towards subtelomeric ends and that large central regions of the chromosomes were
recombination free. This redistribution of COs led us to investigate chromosome dynamics in
wild- type and axr1 meiocytes. We observed that he telomere bouquet in axr1 meiocytes was
not altered. However, the pairing of chromosomes was altered in axr1-/-. We performed FISH
on 3D nuclei with probes labelling either central regions of the chromosomes regions that
almost do not recombine in the mutant or probes that label highly recombinogenic subtelomeric
regions in axr1-/- compared to wild- type. We observed that pairing of central regions was
rarely detected in axr1-/- and it was also affected in subtelomeric regions but to a lesser degree.
We investigated the methylation status of DNA in the axr1 mutant. In somatic cells, DNA was
dramatically hypermethylated compared to wild-type in all contexts (CG, CHG, CHH). This
hypermethylation was also detected in meiotic cells by immunocytology. However, no clear
correlation could be obtained between the methylation status of the DNA and the CO
localization