Actin gene duplication and the evolution of morphological complexity in land plants

Actin is a highly conserved cytoskeletal protein that is a key component of cells. Genes encoding actin occur in single copies in most green algae, in 2-3 copies in bryophytes, and in increasingly more complex gem families in ferns and seed plants. We use the well-resolved phylogenetic frameworks of the Streptophyta as a guide to reconstruct the patterns of actin gene duplication in early diverging land plants. Our working hypothesis is that the origin of novel tissues in the bryophytes (e.g. multicellular sporophyte) may be reflected in the functional diversification of duplicate actin genes in these taxa. Actin is used as a model cytoskeletal protein with the assumption that its evolutionary history represents those of other cytoskeletal elements and the coevolved binding proteins. Here we provide a phylogenetic perspective on the origin of green algal and land plant actin genes and use this information to speculate on the role of plant actin in early plant evolution.