Convergent paths to multicellular complexity in photosynthetic eukaryotes

Multicellularity evolved multiple times independently in eukaryotes and has enabled the emergence of complex organisms with various specialized cell types and organs. While principles governing multicellular development are often studied in each domain of life separately, there are clear similarities in shape and form, likely driven by common ecological challenges or physical constraints. We here explore the analogies in multicellular development and its underpinnings in plants and in brown and red algae — photosynthetic multicellular eukaryotes whose last common ancestor was unicellular. We identify conceptual homologies and discuss examples of common underlying genetic, biochemical, and cellular principles, which we hope will inspire more integrated and comparative investigation into the principles that underlie complex multicellularity.