Telonemia, a new protist phylum with affinity to chromist lineages

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Abstract
Recent molecular investigations of marine samples taken from different environments, including tropical, temperate and polar areas, as well as deep thermal vents, have revealed an unexpectedly high diversity of protists, some of them forming deep-branching clades within important lineages, such as the alveolates and heterokonts. Using the same approach on coastal samples, we have identified a novel group of protist small subunit (SSU) rDNA sequences that do not correspond to any phylogenetic group previously identified. Comparison with other sequences obtained from cultures of heterotrophic protists showed that the environmental sequences grouped together withTelonema, a genus known since 1913 but of uncertain taxonomic affinity. Phylogenetic analyses using four genes (SSU,Hsp90,alpha-tubulinandbeta-tubulin), and accounting for gamma- and covarion-distributed substitution rates, revealedTelonemaas a distinct group of species branching off close to chromist lineages. Consistent with these gene trees,Telonemapossesses ultrastructures revealing both the distinctness of the group and the evolutionary affinity to chromist groups. Altogether, the data suggest thatTelonemaconstitutes a new eukaryotic phylum, here defined as Telonemia, possibly representing a key clade for the understanding of the early evolution of bikont protist groups, such as the proposed chromalveolate supergroup.