Recombination suppression in heterozygotes for a pericentric inversion induces interchromosomal effect on crossovers inArabidopsis

Abstract

26During meiosis, recombination ensures the allele exchange through crossovers (COs) 27 between the homologous chromosomes and, additionally, their proper segregation. CO events are 28 under a strict control but molecular mechanisms underlying CO regulation are still elusive. Some 29 advances in this field were made by structural chromosomal rearrangements that are known at 30 heterozygous state to impair COs in various organisms. In this paper, we have investigated the 31 effect that a large pericentric inversion involving chromosome 3 of Arabidopsis thaliana has on 32 male and female recombination. The inversion associated to a T-DNA dependent mutation likely 33 resulted from a side effect of the T-DNA integration. Reciprocal backcross populations, each 34 consisting of over 400 individuals, obtained from the T-DNA mutant and the wild type, both 35 crossed with Landsberg, have been analyzed at genome-wide level by 143 SNPs. We found a 36 strong suppression of COs in the rearranged region in both male and female meiosis. As expected, 37 we did not detect single COs in the inverted region consistently with the post-meiotic selection 38 operating against unbalanced gametes. Cytological analysis of chiasmata in F1 plants confirmed 39 that COs are effectively dropping in chromosome 3 pair. Indeed, CO failure within the inversion is 40 not altogether counterbalanced by CO increase in the regions outside the inversion on 41 chromosome 3. Strikingly, this CO suppression induces a significant increase of COs in 42 chromosome pairs 1, 2 and 5 in male meiosis. We conclude that these chromosomes acquire 43 additional COs thereby compensating the recombination suppression occurring in chromosome 3, 44 similarly to what has been described as interchromosomal (IC) effect in other organisms. In female 45 meiosis, IC effect is not evident. This may be related to the fact that CO number in female is close 46 to the minimum value imposed by the obligatory CO rule. 47 62 chromosome triggers the global response of the meiocyte to obtain the adequate CO number/cell 63 remains a fascinating question in sexually reproducing species. 4 65 456 457 Author Contributions 458