Estimates of nuclear DNA content in 98 species of brown algae (Phaeophyta)

BACKGROUND AND AIMS Brown algae are critical components of marine ecosystems around the world. However, the genome of only one species of the class has so far been sequenced. This contrasts with numerous sequences available for model organisms such as higher plants, flies or worms. The present communication expands our coverage of DNA content information to 98 species of brown algae with a view to facilitating further genomic investigations of the class. METHODOLOGY The DNA-localizing fluorochrome DAPI (4',6-diamidino-2-phenylindole) and the red blood cell (chicken erythrocyte) standard were used to estimate 2C values by static microspectrophotometry. PRINCIPAL RESULTS 2C DNA contents are reported for 98 species of brown algae, almost doubling the number of estimates available for the class. The present results also expand the reported DNA content range to 0.2-3.6 pg, with several species of Fucales and Laminariales containing apparent polyploid genomes with 2C = 1.8-3.6 pg. CONCLUSIONS The data provide DNA content values for 12 of the 19 recognized orders of brown algae spanning the breadth of the class. Despite earlier contentions concerning DNA content and the presence of oogamy, the present results do not support a correlation between phylogenetic placement and genome size. The closest sister groups to the brown algae have genome sizes on the order of 0.3 pg (e.g. Schizocladiophyceae), suggesting that this may be the ancestral genome size. However, DNA content ranges widely across the class.