Evolution of plastid genomes: inferences from discordant molecular phylogenies

摘要

Substantial morphological, biochemical and genetic diversity exists among photosynthetic eukaryotes. Some of the most conspicuous differences involve plastid-based characters. These features, such as the photosynthetic pigment complement, have provided a basis for defining plant and algal taxa. Christensen (1962) classified algae into three divisions according to their pigment composition. In this system, the division chlorophyta includes plants and algae that possess chlorophylls a and b, the Chromo-phyta are algae that predominantly contain chlorophylls a and c, while the Rhodophyta are defined in part as those algae having primarily chlorophyll a and accessory phycobilin pigments. However, autotrophic eukaryotes evolved in a stepwise manner with the mitochondrial and plastid organelles originating from formerly free-living prokaryotic endo-symbionts (Gray & Doolittle 1982). In examining the evolution of these organisms, one must consider the evolution of not only the host, but also its organelles with their prokaryotic ancestors.