Jim Umen and I have published an article in the newest issue of Annual Review of Genetics. We review some green algae that are or have the potential to be models for the evolution of multicellularity, including Volvox, Ulva, Chara, and Caulerpa. Transitions from unicellular to multicellular (or, in the case of Caulerpa, giant, multinucleate unicellular) have been frequent and varied within the green algae, and we argue that studying diverse examples is necessary to understand how and why these transitions have taken place.

Abstract:

The repeated evolution of multicellularity across the tree of life has profoundly affected the ecology and evolution of nearly all life on Earth. Many of these origins were in different groups of photosynthetic eukaryotes, or algae. Here, we review the evolution and genetics of multicellularity in several groups of green algae, which include the closest relatives of land plants. These include millimeter-scale, motile spheroids of up to 50,000 cells in the volvocine algae; decimeter-scale seaweeds in the genus Ulva (sea lettuce); and very plantlike, meter-scale freshwater algae in the genus Chara (stoneworts). We also describe algae in the genus Caulerpa, which are giant, multinucleate, morphologically complex single cells. In each case, we review the life cycle, phylogeny, and genetics of traits relevant to the evolution of multicellularity, and genetic and genomic resources available for the group in question. Finally, we suggest routes toward developing these groups as model organisms for the evolution of multicellularity.

Umen, J. & M.D. Herron. 2021. Green algal models for multicellularity. Annual Review of Genetics  55:603-632. doi: 10.1146/annurev-genet-032321-091533 Free e-print