The singleMarchantia polymorpha FERONIAhomolog reveals an ancestral role in regulating cellular expansion and integrity

Plant cells are surrounded by a cell wall, a rigid structure that is not only important for cell and organ shape, but crucial for intercellular communication and interactions with the environment. In the flowering plant Arabidopsis thaliana , the 17 members of the Catharanthus roseus RLK1-like ( Cr RLK1L) receptor kinase family are involved in a multitude of physiological and developmental processes, making it difficult to assess their primary or ancestral function. To reduce genetic complexity, we characterized the single Cr RLK1L gene of Marchantia polymorpha , Mp FERONIA (Mp FER ). Plants with reduced Mp FER levels show defects in vegetative development, i.e., rhizoid formation and cell expansion, and have reduced male fertility. In contrast, Mp fer null mutants and overexpression lines severely affect cell integrity and morphogenesis of the gametophyte. Thus, the Cr RLK1L gene family originated from a single gene with an ancestral function in cell expansion and the maintenance of cellular integrity. During land plant evolution, this ancestral gene diversified to fulfil a multitude of specialized physiological and developmental and roles in the formation of both gametophytic and sporophytic structures essential to the life cycle of flowering plants. Summary statement The Cr RLK1L family arose in land plants and the Marchantia polymorpha genome contains a single copy, Mp FER, which is broadly expressed and regulates cell expansion and cell wall integrity.