RESEARCH ARTICLE LEAFY maintains apical stem cell activity during shoot development in the fern Ceratopteris richardii Andrew RG Plackett1†‡, Stephanie J Conway2†§, Kristen D Hewett Hazelton2, Ester H Rabbinowitsch1, Jane A Langdale1*, Vero´ nica S Di Stilio2* 1Department of Plant Sciences, University of Oxford, Oxford, United Kingdom; 2Department of Biology, University of Washington, Seattle, United States Abstract During land plant evolution, determinate spore-bearing axes (retained in extant bryophytes such as mosses) were progressively transformed into indeterminate branching shoots with specialized reproductive axes that form flowers. The LEAFY transcription factor, which is required for the first zygotic cell division in mosses and primarily for floral meristem identity in flowering plants, may have facilitated developmental innovations during these transitions. Mapping *For correspondence: the LEAFY evolutionary trajectory has been challenging, however, because there is no functional
[email protected] overlap between mosses and flowering plants, and no functional data from intervening lineages. (JAL);
[email protected] (VSD) Here, we report a transgenic analysis in the fern Ceratopteris richardii that reveals a role for LEAFY in maintaining cell divisions in the apical stem cells of both haploid and diploid phases of the † These authors contributed lifecycle. These results support an evolutionary trajectory in which an ancestral LEAFY module that equally to this work promotes cell proliferation was progressively co-opted,