The origin of red algae and the evolution of chloroplasts

Chloroplast structure and genome analyses support the hypothesis that three groups of organisms originated from the primary photosynthetic endosymbios is between a cyanobacterium and a eukaryotic host: green plants (green alga e + land plants), red algae and glaucophytes (for example, Cyanophora)(1). Although phylogenies based on several mitochondrial genes support a specifi c green plants/red algae relationship(2,3), the phylogenetic analysis of nu cleus-encoded genes yields inconclusive, sometimes contradictory results(3, 4). To address this problem, we have analysed an alternative nuclear marker , elongation factor 2, and included new red algae and protist sequences. He re we provide significant support for a sisterhood of green plants and red algae. This sisterhood is also significantly supported by a multi-gene anal ysis of a fusion of 13 nuclear markers (5,171 amino acids). In addition, th e analysis of an alternative fusion of 6 nuclear markers (1,938 amino acids ) indicates that glaucophytes may be the closest relatives to the green pla nts/red algae group. Thus, our study provides evidence from nuclear markers for a single primary endosymbiosis at the origin of these groups, and supp orts a kingdom Plantae comprising green plants, red algae and glaucophytes( 5).