Abstract
Analysis of plastid transporter proteins in Arabidopsis suggests a host origin and provides new insights into plastid evolution.
Highlights
It is generally accepted that a single primary endosymbiosis in the Plantae (red, green, and glaucophyte algae) common ancestor gave rise to the ancestral photosynthetic organelle
Important contributions came from the cyanobacterial endosymbiont and Chlamydia-like bacteria likely co-resident in the first algae
Current data suggest that the primary endosymbiosis occurred once in the common ancestor of the red, green, and glaucophyte algae, the Plantae [2,3,4], with the original plastid and the nuclear-encoded machinery for running the organelle spreading in subsequent cell captures to other branches of the eukaryotic tree [5,6,7]
Summary
It is generally accepted that a single primary endosymbiosis in the Plantae (red, green (including land plants), and glaucophyte algae) common ancestor gave rise to the ancestral photosynthetic organelle (plastid). The gradualist view of evolution through mutation-selection suggests that it would have taken millions of years for the captured prokaryote to become fully integrated into the 'host' eukaryote, becoming the site for carbon fixation and for other complex functions, such as lipid, isoprenoid, and amino acid biosynthesis [10]. These processes were associated with the migration of much of the cyanobacterial genome to the host nucleus and development of the complex protein import system that are key shared features among all canonical plastids [3,11,12]. A remarkable exception to the view that endosymbiosis was a gradual process of integration is offered by the katablepharid protist 'Hatena', which undergoes large-scale morphological changes following the engulfment of a green alga [13]
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