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The neddylation pathway regulates the localization of meiotic CO, the pairing ofhomologous chromosomes and the level of DNA methylation in Arabidopsisthaliana
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International audience. Meiotic crossovers (COs) are important for reshuffling genetic information betweenhomologous chromosomes and, are essential for their correct segregation. In all species studied,CO distribution along chromosomes is not homogeneous. The origin of such heterogeneity isstill poorly understood but several lines of evidence point towards chromatin structure andchromosome dynamics issues (Mézard et al., 2015). We previously demonstrated that theneddylation/rubylation pathway of protein modification was a key regulator of the localizationof meiotic COs in A. thaliana (Tagliaro-Jahns et al., 2014). In the axr1-/- mutant (the geneencoding the E1 enzyme of the neddylation complex), COs are mislocalized on chromosomesbut their number is unaffected. We could show that, in axr1, COs were massively redistributedtowards subtelomeric ends and that large central regions of the chromosomes wererecombination free. This redistribution of COs led us to investigate chromosome dynamics inwild- type and axr1 meiocytes. We observed that he telomere bouquet in axr1 meiocytes wasnot altered. However, the pairing of chromosomes was altered in axr1-/-. We performed FISHon 3D nuclei with probes labelling either central regions of the chromosomes regions thatalmost do not recombine in the mutant or probes that label highly recombinogenic subtelomericregions in axr1-/- compared to wild- type. We observed that pairing of central regions wasrarely 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 wasdramatically hypermethylated compared to wild-type in all contexts (CG, CHG, CHH). Thishypermethylation was also detected in meiotic cells by immunocytology. However, no clearcorrelation could be obtained between the methylation status of the DNA and the COlocalization
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