Genome Size Evolution In Gossypium (Cotton): Progress and Prospects

Grover, C., Paterson, A. H., Peterson, D. G., Sanders, W. S., Schmutz, J., Renny-Byfield, S., & Wendell, J. F. (2013). Genome Size Evolution In Gossypium (Cotton): Progress and Prospects. Plant and Animal Genome XXI. San Diego, CA.

Genome sizes vary considerably across all eukaryotes and even among closely related species. The sequence types and mechanisms responsible for genome size variation are of considerable interest, as are the evolutionary dynamics of genome size variation. The genus Gossypium affords a nice opportunity to study the evolution of genome size on both the diploid and polyploid level. Diploid species in Gossypium range nearly three-fold in 1C DNA content, from 885 Mbp in the sequenced D-genome species (Gossypium raimondii) to 2,570 Mbp in the Australian K-genome species G. exiguum. Polyploid cotton species, like many other polyploid species, have a genome size that is slightly less than the sum of the progenitor genome sizes; however, unlike many other model polyploid species, the diploid progenitors themselves range two-fold in 1C content (maternal ~1700 Mbp and paternal ~885 Mbp), providing a unique opportunity to evaluate the consequences of polyploidy for both genome and genome size evolution when parental genome sizes vary substantially. Published research in cotton reveals that the genome size differences among diploid species can be largely attributed to the differential amplification and success of transposable elements in different lineages; however, genome size reduction has also been demonstrated for the species with the smallest genomes, counterbalancing the idea of a growth-only model. At the polyploid level, limited sequencing from two genomic regions has suggested that the rate of deletion has increased in the polyploid species relative to the diploid progenitors, while the rate of insertion has decreased. A wealth of forthcoming resequencing data from a range of Gossypium species, which span both the diploid and polyploid diversity present in the genus, will inform larger and more sophisticated analyses in many areas of cotton research, including the evolution of genome size.