Effect of the Boy-Named Sue Locus on Polyploid Meiosis in Arabidopsis

Polyploidy, whether recent or ancient is ubiquitous in the evolutionary history of plant species. Yet, to become established, newly formed polyploids must find ways to successfully pair, recombine, and segregate more than two sets of chromosomes. For example, the Ph1 locus has been proposed to reduce homoeologous recombination between the different genomes of hexaploid wheat. The exact function of Ph1 and whether other species have developed different solutions remains to be determined. We address these questions by comparing the natural allopolyploid A. suecica to a synthetic one produced by interspecific hybridization between tetraploid Arabidopsis thaliana and Arabidopsis arenosa. We determined that dosage variation and chromosomal translocations consistent with homoeologous pairing were more frequent in the synthetic allopolyploids than in the natural. We crossed the two allopolyploids to each other and obtained an F2 population segregating for the alleles of the adapted allopolyploid. This F2 population displayed frequent dosage variation and deleterious homoeologous recombination and wide variation in meiotic regularity and pollen viability. Genotyping-by-sequencing revealed a strong tendency to retain a single quantitative trait locus, which we named BoY named Sue (BYS) for which the presence of the A. suecica allele was correlated with increased meiotic regularity and pollen viability. Moreover, investigating the pattern of recombination in the F2 suggests a dominant role for BYS in affecting recombination frequencies. Our results suggest the presence of a dominant gain-of-function allele that increases meiotic stability and fertility, possibly via suppressed recombination.