CONICET | Buscador de Institutos y Recursos Humanos

Lignified cell walls are widely considered to be key innovations in the evolution of terrestrial plants from aquatic ancestors, some 475 MYA [1-3]. Lignins, complex aromatic heteropolymers, stiffen and fortify secondary cell walls within xylem tissues, creating a dense matrix that binds cellulose microfibrils [4] and cross-links other wall components [5], and thereby prevents the collapse of conductive vessels, lends biomechanical support to stems, and allows plants to adopt an erect growth habit in air. While lignin-like compounds have been identified in primitive green algae [6, 7], the presence of true lignins in non-vascular organisms, such as aquatic algae, has not been confirmed [2, 3, 8, 9]. Here we report the discovery of secondary walls and lignin within cells of the intertidal red alga Calliarthron cheilosporioides. Until now, such developmentally-specialized cell walls have been described only in vascular plants. Finding secondary walls and lignin in red algae raises many questions about the convergent or deeply-conserved evolutionary history of these traits, as red algae and vascular plants likely diverged more than 1 billion years ago.