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The Role of ASY1 in Promoting Meiotic Stability in Polyploid Arabidopsis

Final Report Summary - POLYMEIO (The Role of ASY1 in Promoting Meiotic Stability in Polyploid Arabidopsis)

Polyploidy is a major contributor to plant evolution but requires meiotic adaptation to be successful. In newly formed polyploids, chromosomes often associate at meiosis with more than one partner leading to unequal chromosome segregation and severe reductions in fertility. By contrast, most naturally-occurring polyploid species show little (if any) defects of chromosome segregation and are highly fertile. The molecular mechanisms responsible for this “adaptation” are just beginning to be unravelled.
Recently, different meiotic proteins (including ASY1) were proposed as playing an important role in the stabilisation of meiosis in autotetraploid Arabidopsis arenosa. It was proposed that meiotic stabilisation in tetraploid A. arenosa is due to a reduction in crossover frequency, possibly due to increased CO interference (the phenomenon that one CO event reduces the likelihood of a second CO nearby), mediated primarily through a tetraploid specific allele of the gene coding one of these proteins (ASY1). This is the working hypothesis we have interrogated in this project. We have also analysed the effect of temperature, another important driver of meiotic adaptation in A. arenosa, on recombination in Arabidopsis.

We confirmed, using a genome-wide analysis of recombination, that tetraploid A arenosa has a single crossover per chromosome. Chromosomes were observed to recombine with each of the three possible partners, indicating that no “pairing-preference” has been established and partner choice is essentially random. Using a high-through put pollen-based assay to measure meiotic recombination, we showed that the tetraploid allele of ASY1 results in reduced recombination rates in several intervals tested. This result suggests that ASY1 is, at least in part, responsible for the reduced recombination observed in tetraploids. We are now confirming the ASY1 results with a genome-wide analysis of recombination.

Temperature also plays an important role in meiotic adaptation in A arenosa. We have shown that Arabidopsis has a U-shaped response to temperature with minimum recombination at 18C and increased recombination at 8C and 28C. Hei10/MLH1 foci counts confirm that the increase in COs observed at 8C and 28C occur via the class I interference sensitive CO pathway.

SC length was shown to be inversely correlated with temperature. This change in SC explains the increase in COs observed at 8C, but not at 28C, suggesting either a breakdown in the CO interference signal at high temperature or some other change to the standard model of CO patterning.