PHYLOGENETIC-RELATIONSHIPS AMONG THE CRYPTOPHYTA - ANALYSES OF NUCLEAR-ENCODED SSU RIBOSOMAL-RNA SEQUENCES SUPPORT THE MONOPHYLY OF EXTANT PLASTID-CONTAINING LINEAGES

The Cryptophyta comprise photoautotrophic protists with complex plasti ds which harbor a remnant eukaryotic nucleus (nucleomorph) and a few h eterotrophic taxa which either lack a plastid (Goniomonas) or contain a complex plastid devoid of pigments (leucoplast; Chilomonas). To reso lve the phylogenetic relationships between photosynthetic, leucoplast- containing and aplastidial taxa, we determined complete nuclear-encode d SSU rRNA-sequences from 12 cryptophyte taxa representing the genera Cryptomonas, Chilomonas, Rhodomonas, Chroomonas, Hemiselmis, Proteomon as and Teleaulax and, as an outgroup taxon, Cyanoptyche gloeocystis (G laucocystophyta). Phylogenetic analyses of SSU rRNA sequences from a t otal of 24 cryptophyte taxa rooted with 4 glaucocystophyte taxa using distance, parsimony and likelihood methods as well as LogDet transform ations invariably position the aplastidial genus Goniomonas as a siste r taxon to a monophyletic lineage consisting of all plastid-containing cryptophytes including Chilomonas. Among the plastid-containing taxa, we identify six major clades each supported by high bootstrap values: clade I (Cryptomonas and Chilomonas), clade II (Rhodomonas, Pyrenomon as, Rhinomonas and Storeatula), clade III (Guillardia and the 'unident ified cryptophyte' strain CCMP 325), clade IV (Teleaulax and Geminiger a), clade V (Proteomonas) and clade VI (Hemiselmis, Chroomonas and Kom ma). Clade I (Cryptomonas and Chilomonas) represents a sister group to clades II-VI which together form a monophyletic lineage the phylogene tic relationships between clades Il-VI remain largely unresolved. Chil omonas is positioned within the Cryptomonas clade and thus presumably evolved from a photosynthetic taxon of this genus. In our analysis the characters blue and red pigmentation do not correspond with a basal s ubdivision of the phylum, thus rejecting this character for higher-lev el classification of cryptophytes. However, different spectroscopic su btypes of phycoerythrin (PE I-III) and phycocyanin (PC Ii-IV) represen t informative characters at a lower taxonomic level. Phycocyanin types are confined to the later diverging clade VI and within Hemiselmis, a species with phycocyanin is monophyletic with two species containing phycoerythrin. This supports previous molecular studies which demonstr ated that the beta subunit of all cryptophyte biliproteins, regardless of spectroscopic type, is phylogenetically derived from the red algal P-phycoerythrin gene family, therefore the cryptophyte phycocyanins p resumably originated by chromophore replacement from phycoerythrin. Ou r phylogenetic analysis does not support a previous suggestion that th e aplastidial cryptophyte Goniomonas evolved from an ancestor containi ng a complex cryptomonad-type plastid by nucleomorph and plastid loss.