The phenotype of the CRINKLY4 deletion mutant of Physcomitrella patens suggests a broad role in developmental regulation in early land plants.

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conclusionsDeletion of the ancestral gene of the land plant multigene family of receptor like kinase CR4 in Physcomitrella patens demonstrates involvement in developmental control of gametophytic and sporophytic organs. The CRINKLY4 (CR4) family of receptor kinases in angiosperms consists of three clades, one including CR4, the CR4-related CCR1 and CCR2, a second including CCR3 and CCR4 family members, and a third and more distant clade. In addition to crinkly leaves in maize, which gave rise to the mutant gene name, CR4 is implicated in ovule, embryo, flower and root development in Arabidopsis thaliana. In root tips of the same species the module including a CLAVATA3/ESR-related protein, an Arabidopsis CR4, a CLAVATA1 and a WUSCHEL-related homeobox 5 (CLE40-ACR4-CLV1-WOX5) is implicated in meristem cell regulation. In embryos and shoots, CR4 acts together with A. thaliana MERISTEM LAYER 1 and PROTODERMAL FACTOR 2 to promote A. thaliana epidermis differentiation. Phylogenetic analysis has demonstrated that early land plants, e.g. mosses carry a single ancestral CR4 gene, together with genes encoding the other members of the CLE40-ACR4-CLV1-WOX5 signaling module. Here we show that CR4 serves as a broad regulator of morphogenesis both in gametophyte phyllids, archegonia and in sporophyte epidermis of the moss Physcomitrella patens. The phenotype of the CR4 deletion mutant in moss provides insight into the role of the ancestral CR4 gene as a regulator of development in early land plants.