Rosa canina Genome sequencing and assembly

Sexual reproduction depends on stable meiotic chromosome pairing, which is challenged in polyploids due to the coexistence of multiple subgenomes. The pentaploid dogrose Rosa canina (2n=5x=35) showcases that by presenting a unique asymmetric chromosome pairing: one subgenome forms bivalents and is inherited bisexually, while three subgenomes form maternally inherited univalents. Here, we present a haplotype-phased chromosome-level genome of the pentaploid (2n=5x=35) Rosa canina. (Rosa sect. Caninae) We identified that the pairing subgenome consists of two highly syntenic homozygous copies, preferentially composed centromeres enriched with Ty3/gypsy Athila retroelement. In contrast univalent-forming non-pairing subgenomes were more divergent and revealed centromeres mainly composed of tandem repeats. We further reveal that subgenomes originated from different clades across the genus Rosa. Analyses of monoploid pollen from several dogrose species revealed that subgenomes of different phylogenetic origins are capable of forming bivalents. The mating behaviour is therefore controlled by the degree of synteny between the chromosomes rather than by the phylogenetic background of a subgenome. The different types of centromeres found hint at a possible role in the preferential segregation of univalents during asymmetric female meiosis.