Molecular Systematics of Plants II

pp 375-409

The Origin and Evolution of Plastids and Their Genomes

  • Jeffrey D. Palmer
  • , Charles F. Delwiche

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Plastids, the eukaryotic organelles responsible for photosynthesis and other biochemical tasks, are semiautonomous endosymbionts derived from previously free-living cyanobacteria (Gray, 1992; Douglas, 1994; Loiseaux-de Göer, 1994; Bhattacharya and Medlin, 1995). In this chapter we discuss, with an emphasis on molecular phylogenetic evidence, our current understanding of the origin and diversification of these organelles, provide an overview of plastid diversity in the context of endosymbiosis, and discuss the evolution of plastid genomes from that of a cyanobacterium. We place particular emphasis on the evidence from different cellular genomes—nuclear, plastid, and mitochondri al—that bears on the fundamental question of whether all plastids are derived from a single endosymbiotic event, or from two or more independent events. Although the bulk of the data support a monophyletic origin of plastids, some evidence, particularly from the nuclear genome, suggests at least two independent endosymbiotic events.