3-D Growth: the diversity of strategies in brown algae

Brown algae developed multicellularity independently of plants and animals. Once formed, the embryo rapidly establishes growth hotspots that lay the foundation for the development of the adult stage. The mechanisms that control the establishment of these growth hotspots are unknown.

Using diagrams and 3-D schematics, this review unpacks the different growth strategies of these organisms, focusing on localized 3-D growth in a particular cell or tissue. The sequence of cell divisions leading to the formation of 3-D tissues is compared among algae of the orders Sphacelariales, Dictyotales, Laminariales and Fucales, thereby providing an overview of the range of growth strategies selected in this phylum. I specifically focus on the orientation of cell divisions, which generally alternates in most brown algae, being perpendicular to the previous plane of cell division. These cell division characteristics, specific to brown algae, implement the building plans of 3-D bodies.

This review highlights the diversity of 3-D growth strategies within the brown algae, illustrating several cases and providing a framework for a broader comparison with other multicellular organisms, which developed 3-D tissues elsewhere within the eukaryote tree. It also addresses the potential underlying cellular mechanisms that control cell division plane orientation, and questions the level of cell autonomy with respect to neighbouring cells and the external environment.