After the primary endosymbiosis: an update on the chromalveolate hypothesis and the origins of algae with Chl <Emphasis Type="Italic">c</Emphasis> |
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Authors: | Beverley R Green |
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Institution: | (1) Botany Department, University of British Columbia, Vancouver, B.C, V6T 1Z4, Canada |
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Abstract: | The chromalveolate hypothesis proposed by Cavalier-Smith (J Euk Microbiol 46:347–366, 1999) suggested that all the algae with chlorophyll c (heterokonts, haptophytes, cryptophytes, and dinoflagellates), as well as the ciliates, apicomplexans, oomycetes, and other
non-photosynthetic relatives, shared a common ancestor that acquired a chloroplast by secondary endosymbiosis of a red alga.
Much of the evidence from plastid and nuclear genomes supports a red algal origin for plastids of the photosynthetic lineages,
but the number of secondary endosymbioses and the number of plastid losses have not been resolved. The issue is complicated
by the fact that nuclear genomes are mosaics of genes acquired over a very long time period, not only by vertical descent
but also by endosymbiotic and horizontal gene transfer. Phylogenomic analysis of the available whole-genome data has suggested
major alterations to our view of eukaryotic evolution, and given rise to alternative models. The next few years may see even
more changes once a more representative collection of sequenced genomes becomes available. |
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