A deep dive into bryophyte genome space reveals opposing evolutionary trends in the sister lineages, mosses and liverworts

Among the lineages of the tree of life, land plants exhibit a remarkably high genomic disparity because of their distinct evolutionary trajectories in the phylogenetic history of their major lineages. The macroevolutionary pattern of genomic evolution has been mainly investigated to obtain insights into well-studied lineages such as angiosperms, but little attention has been given to many important lineages such as bryophytes. This study was designed to resolve this gap by comparing the genomic evolution trajectories of mosses and liverworts. Thus, a data set comprising chromosome number and genome size was compiled, including previously published and newly generated data that were used to trace the phylogenetic history of these two parameters among mosses and liverworts via ancestral state reconstruction and phylogenetic comparative analyses. Contrasting patterns of chromosome number and genome size evolutions were detected between the two sister lineages. Mosses accumulated high chromosome number disparity via repeated whole-genome duplications and descending dysploidy but maintained a small genome size. By contrast, the chromosome number of liverworts was highly conserved, and heterogeneous trends in genome size evolution were identified among major lineages. These contrasting patterns may be partly explained by the difference in genomic dynamics: Active dynamics enables genome downsizing and reorganization in mosses, whereas genome stability leads to the accumulation of large genomes in liverworts. The results of this study confirmed the distinct trends of genomic evolution in bryophytes.