Photosynthetic eukaryotes unite: endosymbiosis connects the dots.
The photosynthetic organelle of algae and plants (the plastid) traces its origin to a primary endosymbiotic event in which a previously non-photosynthetic protist engulfed and enslaved a cyanobacterium. This eukaryote then gave rise to the red, green and glaucophyte algae. However, many algal lineages, such as the chlorophyll c-containing chromists, have a more complicated evolutionary history involving a secondary endosymbiotic event, in which a protist engulfed an existing eukaryotic alga (in this case, a red alga). Chromists such as diatoms and kelps then rose to great importance in aquatic habitats. Another algal group, the dinoflagellates, has undergone tertiary (engulfment of a secondary plastid) and even quaternary endosymbioses. In this review, we examine algal diversity and show endosymbiosis to be a major force in algal evolution. This area of research has advanced rapidly and long-standing issues such as the chromalveolate hypothesis and the extent of endosymbiotic gene transfer have recently been clarified.
Bhattacharya
Debashish
D
Department of Biological Sciences and Center for Comparative Genomics, University of Iowa, Iowa City, Iowa 52242-1324, USA. dbhattac@blue.weeg.uiowa.edu
Yoon
Hwan Su
HS
Hackett
Jeremiah D
JD
D000818:Animals; D002734:Chlorophyll / Q000502:physiology; D017377:Diatoms; D056890:Eukaryota / Q000502:physiology*; D008954:Models, Biological; D010788:Photosynthesis; D010802:Phylogeny; D018521:Plant Physiological Phenomena; D018087:Plastids / Q000502:physiology; D013559:Symbiosis
D002734:Chlorophyll