HETEROZYGOUS INVERSION INDUCES INTERCHROMOSOMAL EFFECT IN ARABIDOPSIS MEIOTIC RECOMBINATION

During meiosis, recombination ensures allelic exchange through crossovers (COs) between the homologous chromosomes. Advances in comprehension of CO rules benefit from studies of mutations including structural chromosomal rearrangements that, when heterozygous, are known to impair COs in various organisms. In this work, we have investigated the effect of a large heterozygous pericentric inversion on male and female recombination in Arabidopsis. The inversion was discovered in Atmcc1 mutant background and it was characterized through genetic and NGS analysis. Reciprocal backcross populations, each consisting of over 400 individuals, obtained from mutant and wild type, both crossed with Landsberg, have been analyzed genome-wide by 143 SNPs. Firstly, the negative impact of inversion became evident in terms of CO loss in the rearranged chromosome in both male and female meiosis. As expected, no one-CO event was detected within the inversion, consistent with a post-meiotic selection operating against unbalanced gametes. Cytological analysis of chiasmata in F1 plants confirmed that COs were reduced in male meiosis in the chromosome carrying the inversion. Interestingly, CO suppression on the rearranged chromosome is associated with a significant increase of COs in the other chromosomes thereby maintaining unchanged the CO number per cell. The CO pattern that we observe in our study is consistent with the interchromosomal (IC) effect as it was first described in Drosophila. In contrast to male meiosis, in female meiosis no IC effect is visible. This may be related to the interference strength that constrains the CO number in excess of the minimum value imposed by CO assurance in Arabidopsis female meiosis.