Streptophyte algae and terrestrialization: breaking down the fundamental challenges from an ECM perspective

The successful conquest of land by ancient streptophyte algae is closely related to the structural features and functional roles of their extracellular matrix and associated evolutionary innovations. Terrestrialization 500+ million years ago required adaptation to multiple and novel abiotic and biotic stressors. The establishment of a sessile habit which encompasses adhesion likely required special cell surface components like arabinogalactan protein-like macromolecules. The secretion of polysaccharide-rich extracellular polymeric substance (EPS) provided multiple services including establishment of a platform for interactions with surrounding microorganisms, i.e., biofilms. Protection against harmful UV radiation likely included production of phenolic compounds, cuticular components and sporopollenin. Innovations to the various components of the cell wall contributed to the evolution of multicellularity and large thallus sizes, water retention, defense, wound response and interactions with surrounding microorganisms. Yet we are only in an infancy stage in understanding how specific cell wall components contributed to the invasion of land by streptophyte algae. Future studies are needed that encompass much larger taxonomic screening, detailed glycomics and proteomics, mining of biosynthetic pathways and comprehensive analyses of cell wall integrity especially in response to abiotic and biotic stressors of terrestrial habitats.