Is GC-content Correlated with Genome Size in Plants

GC base pair content is an important character in the description of new taxa of prokaryotes, but its role in plant systematics and evolution is still poorly understood. Although GC content is positively correlated with genome size in bacteria and vertebrates (1) there is debate about how those two factors are related in plants. Barow and Meister (2) estimated base composition and genome size in 54 taxa of angiosperms and gymnosperms, and their findings did not support Vinogradov (1) proposition stating that there is a positive correlation between GC content and genome size. More recently, Barow and Meister (3) confirmed that base composition and genome size were not correlated using an expanded sampling of 215 plant species measured by numerous authors over the last 14 years. Using flow cytometry methods (FCM) with PI and DAPI, we estimated base composition in closely related species of Apiaceae (16 spp.), Brassicaceae (30 spp.), Cyperaceae (135 spp.), Onagraceae (15 spp.), Poaceae (132 spp.) and Salicaceae (20 spp.), and found a significant positive correlation between GC content and either genome size or monoploid genome size. Sequence data of 11 Oryza species (4) independently supported our FCM results and suggested that GC and genome size correlation is explained by genomic repeats and interspecific genome size variation found within closely related taxa. 1. Vinogradov AE (1994): Cytometry 16: 34-40. 2. Barow M & Meister A (2002): Cytometry 47: 1-7. 3. Meister A & Barow M (2007): Analysis of Base Composition by Flow Cytometry. In: Doležel J et al. (eds.), Flow Cytometry with Plant Cells. Wiley, Weinheim, pp. 177-215. 4. Ammiraju JSS et al. (2006): Genome Research 16: 140-147.