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1 November 2004 HSP90, Tubulin and Actin are Retained in the Tertiary Endosymbiont Genome of Kryptoperidinium foliaceum
MICHELLE L. McEWAN, PATRICK J. KEELING
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Abstract

The dinoflagellate Kryptoperidinium foliaceum has replaced its ancestral peridinin-containing plastid with a fucoxanthin-containing diatom plastid via tertiary endosymbiosis. The diatom endosymbiont of K. foliaceum is much less reduced than well-studied endosymbiotic intermediates, such as cryptophytes and chlorarachniophytes, where relict nuclear genomes are retained in secondary endosymbionts. The K. foliaceum endosymbiont retains a prominent nucleus, multiple four-membrane plastids, and mitochondria, all within a relatively large volume of cytoplasm that is separated from the host cytoplasm by a single membrane. Here we report the first protein-coding gene sequences from the K. foliaceum endosymbiont and host nuclear genomes. We have characterised genes for nucleus-encoded cytosolic proteins, actin (from endosymbiont), alpha-tubulin (from both), beta-tubulin (from host), and HSP90 (from both), in addition to homologues from pennate diatoms Nitzschia thermalis and Phaeodactylum tricornutum. Phylogenetic reconstruction shows that the actin is diatom-derived, the beta-tubulin dinoflagellate-derived, while both diatom- and dinoflagellate-derived alpha-tubulin and HSP90 genes were found. The base composition biases of these genes co-varied with their phylogenetic position, suggesting that the genes still reside in their respective genomes. The presence of these genes implies they are still functional and more generally indicates that the endosymbiont is less genetically reduced than those of cryptophytes or chlorarachniophytes, raising the interesting question of whether any genes have transferred between the two nuclear genomes.

MICHELLE L. McEWAN and PATRICK J. KEELING "HSP90, Tubulin and Actin are Retained in the Tertiary Endosymbiont Genome of Kryptoperidinium foliaceum," The Journal of Eukaryotic Microbiology 51(6), 651-659, (1 November 2004). https://doi.org/10.1111/j.1550-7408.2004.tb00604.x
Received: 27 February 2004; Accepted: 18 August 2004; Published: 1 November 2004
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