Abstract
In terms of genome size (i.e. the amount of DNA in the nucleus), monocots are remarkably diverse, with values ranging over 1000-fold from 1C = 147 Mbp in Carex paxii to 148,852 Mbp in octoploid Paris japonica. Nevertheless, most species surveyed to date possess small genomes (1C mode = 500 Mbp) and the few species with giant genomes (1C> 35,000 Mbp) are phylogenetically restricted to derived positions within Liliales, Asparagales and commelinids. In recent years there has been substantial progress in understanding the molecular processes responsible for generating such genome diversity, and the application of next generation sequencing (NGS) technologies to monocots with small and intermediate sized genomes have provided important insights into their molecular composition, structure and evolution. Nevertheless, there is only limited molecular information outside of Poaceae, and a dearth of data for species with giant genomes.
To address this issue we have used NGS to analyze the most highly represented sequences in the giant genomes of Fritillaria (Liliaceae) where 1C-values range from 30,000 – 100,000 Mbp (including the largest diploid genomes ever recorded in plants). The data indicate that these obese genomes are remarkably different from small to medium sized genomes where differences in genome size are generated through changes in abundance of just one or a few highly abundant repeats. In contrast, for the species examined to date, the bulk of their genomes are made up of highly heterogenous sets of repeats, each of which has a relatively low abundance in terms of the total % of the genome. The implications of these findings to understanding genome size diversity and evolution will be discussed.