Evolution of Chiasma Patterning: A Route to Stable Polyploids?

Plants are frequently polyploid, possessing upwards of two sets of chromosomes. Allopolyploids arise through hybridization of genomes from species with closely related, yet distinct homeologous chromosomes. Genome doubling within a species gives rise to autopolyploids which possess multiple copies of identical homologous chromosomes. Both forms of polyploidy create a particular challenge to ensure accurate chromosome segregation in meiosis. In each case the meiotic imperative is to behave as a diploid during meiosis. A variety of, as yet poorly understood mechanisms, have evolved to stabilize meiosis in polyploids. Here we focus on the analysis of meiotic behavior in autotetraploid Arabidopsis arenosa where recent studies suggest modifications in chiasma distribution associated with subtle changes in the proteins that constitute the chromosome axis, have contributed to meiotic stabilization following whole genome duplication. Cytological analysis of chromosome remodeling during meiotic prophase is consistent with recent models that suggest crossover interference is mediated via the chromosome axis. We propose that an increase in interference may underlie the change in chiasma distribution observed in A. arenosa tetraploids.