Format: ORAL

Hannah McConnell1, Jancee Rice Lanclos1, Nicholas Gjording1, Genevieve Stockman1, Julin Maloof2, Andrew Plackett3 and Vernica S. Di Stilio1

1-Department of Biology, University of Washington, Seattle, USA 2-Department of Plant Biology, University of California, Davis, USA 3-School of Biosciences, University of Birmingham, Birmingham, UK

The transition from vegetative growth to flowering in the diploid sporophyte of angiosperms is partly controlled by LEAFY (LFY), a well-characterized flower meristem identity gene. Less is known about whether LFY plays a role in the haploid gametophyte phase and what that role might be. LFY orthologs also exist in non-flowering plants, and in mosses, they control the first mitotic division of the zygote. Recent evidence indicates that LFY has a vegetative role in fern meristems, but it is unclear where its reproductive function arose. Here, we continue to bridge the gap in investigations into this key floral regulator between mosses and angiosperms to reconstruct the evolution of LFYs reproductive function across land plants. We ask whether LFY was co-opted into its specialized flowering function from its previously identified generalized role in regulating meristems by characterizing its two paralogs in the model fern Ceratopteris richardii. Transgenic ferns constitutively overexpressing LFY orthologs experienced delayed gametophyte fertilization, suggesting a novel role in gametophyte reproduction, and produced overgrown lateral meristems and decreased leaf compounding in sporophytes, providing additional support to the previously characterized vegetative meristem function. Overall, our results suggest that LFYs reproductive role in angiosperm sporophytes may have been ancestrally co-opted from the gametophyte while also supporting previous evidence of their involvement in cell division in both phases of the fern life cycle.