The Ceratodon Genome Project

The evolution of separate sexes is predicted to have major consequences for genome architecture and patterns of polymorphism. We have begun to evaluate these predictions in the bryophytes, a lineage of plants that has evolved separate sexes multiple times, providing us with a well-replicated natural experiment. We first determined the genome sequence of the Ceratodon purpureus female lab strain GG1. The main genome scaffold sequence contains 339.6 MB (N/L50: 259/381.1 KB). The 1140 scaffolds > 50 KB contain 92.1% of the sequence space.  To assemble the scaffolds into chromosomes, we sequenced at low coverage a mapping population generated between GG1 and R40, a male laboratory isolate. Because the non-recombining U and V sex chromosomes cannot be assembled using a genetic map, we also constructed and end-sequenced a BAC library, and shotgun sequenced putative sex-linked BAC clones. We have also generated male and female transcriptomes of the gametophyte stage of C. purpureus, as well as low coverage resequencing of 23 additional isolates from across the distribution of the species. Preliminary analyses of the genome show that the sex chromosomes are much less polymorphic and have lower gene density than the autosomes, but also that the sex chromosomes have recently acquired new genes. These data provide a foundation for understanding the genetic basis of sexual dimorphism.