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Chromalveolate plastids: direct descent or multiple endosymbioses?

2009; Elsevier BV; Volume: 24; Issue: 3 Linguagem: Inglês

10.1016/j.tree.2008.11.003

1872-8383

Andrzej Bodył, John W. Stiller, Paweł Mackiewicz,

Genomics and Phylogenetic Studies

In their recent Opinion article on endosymbiosis and the tree of life, Lane and Archibald [ 1 Lane C.E. Archibald J.M. The eukaryotic tree of life: endosymbiosis takes its TOL. Trends Ecol. Evol. 2008; 23: 268-275 Abstract Full Text Full Text PDF PubMed Scopus (135) Google Scholar ] focused on the chromalveolate hypothesis [ 2 Cavalier-Smith T. Principles of protein and lipid targeting in secondary symbiogenesis: euglenoid, dinoflagellate, and sporozoan plastid origins and the eukaryote family tree. J. Eukaryot. Microbiol. 1999; 46: 347-366 Crossref PubMed Scopus (510) Google Scholar ] that all eukaryotes with plastids derived secondarily from a red alga are descended directly from a single, common ancestor. They pointed out that no data actually support a monophyletic grouping of all these taxa, and highlighted growing phylogenetic conflicts with the traditional Chromalveolata. To resolve these contradictions, they offered an expanded version of the 'chromalveolates,' with additional independent plastid losses from the added heterotrophic lineages. More recent phylogenetic analyses suggest that, if a model of direct vertical descent of these plastids is to be accommodated, further expansions of the original Chromalveolata are needed [ 3 Burki F. et al. Phylogenomics reveals a new 'megagroup' including most photosynthetic eukaryotes. Biol. Lett. 2008; 4: 366-369 Crossref PubMed Scopus (207) Google Scholar , 4 Patron N.J. et al. Multiple gene phylogenies support the monophyly of cryptomonad and haptophyte host lineages. Curr. Biol. 2007; 17: 887-891 Abstract Full Text Full Text PDF PubMed Scopus (104) Google Scholar , 5 Kim E. Graham L.E. EEF2 analysis challenges the monophyly of Archaeplastida and Chromalveolata. PLoS ONE. 2008; 3: e2621 Crossref PubMed Scopus (48) Google Scholar ]. In fact, several investigations, including perhaps the broadest combined sampling of genes and taxa to date [ 3 Burki F. et al. Phylogenomics reveals a new 'megagroup' including most photosynthetic eukaryotes. Biol. Lett. 2008; 4: 366-369 Crossref PubMed Scopus (207) Google Scholar ], indicate that Archaeplastida (=Plantae) is descended from the same ancestor as chromalveolate taxa [ 3 Burki F. et al. Phylogenomics reveals a new 'megagroup' including most photosynthetic eukaryotes. Biol. Lett. 2008; 4: 366-369 Crossref PubMed Scopus (207) Google Scholar , 4 Patron N.J. et al. Multiple gene phylogenies support the monophyly of cryptomonad and haptophyte host lineages. Curr. Biol. 2007; 17: 887-891 Abstract Full Text Full Text PDF PubMed Scopus (104) Google Scholar , 5 Kim E. Graham L.E. EEF2 analysis challenges the monophyly of Archaeplastida and Chromalveolata. PLoS ONE. 2008; 3: e2621 Crossref PubMed Scopus (48) Google Scholar ]. Interpreted within the confines of the chromalveolate model of plastid descent, this would require a secondary red algal endosymbiont to have existed before red algae ever originated, clearly an evolutionary impossibility (Figure 1).