Phylogenetic analysis of small and large subunits of rDNA genes suggested that Foraminifera originated early in the evolution of eukaryotes, preceding the origin of other rhizopodial protists. This view was recently challenged by the analysis of actin and ubiquitin protein sequences, which revealed a close relationship between Foraminifera and Cercozoa, an assemblage of various filose amoebae and amoeboflagellates that branch in the so-called crown of the SSU rDNA tree of eukaryotes. To further test this hypothesis, we sequenced a fragment of the largest subunit of the RNA polymerase II (RPB1) from five foraminiferans, two cercozoans and the testate filosean Gromia oviformis. Analysis of our data confirms a close relationship between Foraminifera and Cercozoa and points to Gromia as the closest relative of Foraminifera.
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