Early origin of foraminifera suggested by SSU rRNA gene sequences

Foraminifera are one of the largest groups of unicellular eukaryotes withprobably the best known fossil record. However, the origin of foraminiferaand their phylogenetic relationships with other eukaryotes are not wellestablished. In particular, two recent reports, based on ribosomal RNA genesequences, have reached strikingly different conclusions aboutforaminifera's evolutionary position within eukaryotes. Here, we presentthe complete small subunit (SSU) rRNA gene sequences of three species offoraminifera. Phylogenetic analysis of these sequences indicates that theybranch very deeply in the eukaryotic evolutionary tree: later than those ofthe amitochondrial Archezoa, but earlier than those of the Euglenozoa andother mitochondria-bearing phyla. Foraminifera are clearly among theearliest eukaryotes with mitochondria, but because of the peculiar natureof their SSU genes we cannot be certain that they diverged first, as ourdata suggest.