Phylogeny and Molecular Evolution of the Green Algae

Abstract

The green lineage (Viridiplantae) comprises the green algae and their descendants the land plants, and is one of the major groups of oxygenic photosynthetic eukaryotes. Current hypotheses posit the early divergence of two discrete clades from an ancestral green flagellate. One clade, the Chlorophyta, comprises the early diverging prasinophytes, which gave rise to the core chlorophytes. The other clade, the Streptophyta, includes the charophyte green algae from which the land plants evolved. Multi-marker and genome scale phylogenetic studies have greatly improved our understanding of broad-scale relationships of the green lineage, yet many questions persist, including the branching orders of the prasinophyte lineages, the relationships among core chlorophyte clades (Chlorodendrophyceae, Ulvophyceae, Trebouxiophyceae and Chlorophyceae), and the relationships among the streptophytes. Current phylogenetic hypotheses provide an evolutionary framework for molecular evolutionary studies and comparative genomics. This review summarizes our current understanding of organelle genome evolution in the green algae, genomic insights into the ecology of oceanic picoplanktonic prasinophytes, molecular mechanisms underlying the evolution of complexity in volvocine green algae, and the evolution of genetic codes and the translational apparatus in green seaweeds. Finally, we discuss molecular evolution in the streptophyte lineage, emphasizing the genetic facilitation of land plant origins.

Keywords:

• Chlorophyta
• Charophyta
• endosymbiosis
• molecular evolution
• origin of embryophytes
• Prasinophyceae
• phylogeny
• Streptophyta

ACKNOWLEDGMENTS

We are grateful to Pavel kaloud, Fabio Rindi, Juan López-Bautista, Frederick Zechman, Marvin Fawley, Aurora Nedelcu, Marc Buchheim, Andrey Gontcharov, Burkhard Becker and Richard McCourt for discussions and comments on the manuscript. We thank Bob Andersen, Jordi Regas, Antonio Guillén, William Bourland, Jason Oyadomari, Giuseppe Vago, Tom Schils, Antoni López-Arenas, Nadia Abdelahad and Deborah Shelton for providing photographs. Support was provided by FWO-Flanders (FL, HV and ODC).

Notes

Various names have been proposed for the lineage comprising the green algae and land plants: “Viridiplantae” or “Viridaeplantae” (Cavalier-Smith, 1981, 1998), “Chlorobiota” or “Chlorobionta” (Jeffrey, 1971, 1982), “Chloro-plastida” (Adl et al. 2005), or simply “green plants” (Sluiman et al., 1983) or “green lineage.”