What Role can the Meiotic Axis Play in Stabilising Polyploid Meiosis?

Autopolyploid species are widespread within the plant kingdom and offer several putative evolutionary advantages relative to their diploid counterparts. However, in autopolyploids the presence of multiple homologous chromosomes with equal pairing capabilities can result in meiotic irregularities such as multivalent formation and chromosome mis-segregation.

Arabidopsis arenosa has naturally evolved diploid (2n=16) and tetraploid (2n=32) populations and has recently become established as a model organism for investigating autopolyploid meiosis. It has previously been demonstrated that tetraploid A. arenosa has reduced crossover rates when compared with the diploid and it is proposed that this enables meiotic stabilisation by inhibiting multivalent formation and promoting bivalent-like pairing. It has also been shown that a number of genes involved in meiotic axis formation, sister chromatid cohesion and homologue synapsis have undergone strong ploidy-specific differentiation in A. arenosa. For instance, one protein that has undergone selection in the tetraploid A. arenosa lineage is the chromosome axis protein ASY1, the plant functional homologue of HOP1 in S. cerevisiae.

We have used a combination of cytogenetics and immunocytochemistry to further our understanding of how axis formation and synapsis progress in A. arenosa and to determine whether any meiotic differences can be observed in tetraploid A. arenosa plants expressing either the diploid or tetraploid ASY1 allele. Using the same techniques we have also examined the effect that reduced crossovers can have on autopolyploid meiosis in A. thaliana using colchicine induced neo-tetraploid lines of meiotic axis mutants. Progress in both of these areas will be discussed.