Journal
CURRENT BIOLOGY
Volume 18, Issue 13, Pages 956-962Publisher
CELL PRESS
DOI: 10.1016/j.cub.2008.05.042
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Funding
- NIEHS NIH HHS [R01 ES013679, R01ES013679, R01 ES013679-01A2] Funding Source: Medline
- NIGMS NIH HHS [T32 GM008629] Funding Source: Medline
- Direct For Biological Sciences
- Div Of Molecular and Cellular Bioscience [0946528] Funding Source: National Science Foundation
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Plantae (as defined by Cavalier-Smith, 1981) [1] plastids evolved via primary endosymbiosis whereby a heterotrophic protist enslaved a photosynthetic cyanobacterium. This primary plastid spread into other eukaryotes via secondary endosymbiosis. An important but contentious theory in algal evolution is the chromalveolate hypothesis that posits chromists (cryptophytes, haptophytes, and stramenopiles) and alveolates (ciliates, apicomplexans, and dinoflagellates) share a common ancestor that contained a red-algal-derived secondary plastid [2]. Under this view, the existence of several later-diverging plastid-lacking chromalveolates such as ciliates and oomycetes; would be explained by plastid loss in these lineages. To test the idea of a photosynthetic ancestry for ciliates, we used the 27,446 predicted proteins from the macronuclear genome of Tetrahymena thermophila to query prokaryotic and eukaryotic genomes. We identified 16 proteins of possible algal origin in the ciliates Tetrahymena and Paramecium tetraurelia. Fourteen of these are present in other chromalveolates. Here we compare and contrast the likely scenarios for algal-gene origin in ciliates either via multiple rounds of horizontal gene transfer (HGT) from algal prey or symbionts, or through endosymbiotic gene transfer (EGT) during a putative photosynthetic phase in their evolution.
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