The origin of red algae and cryptomonad nucleomorphs: A comparative phylogeny based on small and large subunit rRNA sequences of Palmaria palmata, Gracilaria verrucosa, and the Guillardia theta nucleomorph

The complete large subunit rRNA sequences from the red algae Palmaria palma ta and Gracilaria verrucosa, and from the nucleomorph of the cryptomonad Gu illardia theta, were determined in order to assess their phylogenetic relat ionships relative to each other and to other eukaryotes. Neighbor-joining, maximum-parsimony, and maximum-likelihood trees were constructed on the bas is of small subunit rRNA, large subunit rRNA, and a combination of both mol ecules. Our results support the hypothesis that the cryptomonad plastid is derived from a primitive red alga, in that an ancient common ancestor of rh odophytes and cryptomonad nucleomorphs is indicated. This cluster shows som e affinity with chlorobionts, which could point to a monophyletic origin of green and red plastids. However, the exact branching order of the crown eu karyotes remains uncertain and further research is required. (C) 1998 Acade mic Press.