Format: ORAL

ElissaS. Sorojsrisom1,2, Eva Uddin3, Tynisha Smalls2, Barbara A. Ambrose2

1 Columbia University. New York, NY, USA 2 New York Botanical Garden. Bronx, NY. USA. 3 The Bronx High School of Science. Bronx, NY. USA.

The fundamental sexual reproductive structures of the gametophyte are the archegonium and antheridium (together called gametangia), which produce egg and sperm respectively. The gametangia show remarkable morphological conservation across nonvascular and free-sporing vascular plantsbut are structurally reduced in seed plants. Many studies have investigated the molecular genetics of gametophyte development in angiosperms, as well as in some Bryophytes, but broad comparative studies are lacking. Furthermore, whether and how the gametes produced by the gametangia are homologousacross green algae and land plants is not known. Although analyses of patterning provide strong working hypotheses, contributions from molecular genetics and functional studies will be necessary to determine the complete story of how these structures and the gametes they produce have changed throughout the evolution of land plants. We aim to fill this gap with developmental genetic analyses in the model fern,Ceratopterisrichardii, using a transcriptomic and candidate gene approach. Using bulk RNA-seq of six developmental stages, we developed a time series transcriptome atlas for the gametophyte ofC.richardii. This dataset has allowed us to understand broad patterns of gene expression changes throughout gametophyte development, investigate dynamics of shared vs. unique gene expression between life stages, and identify promising targets for further functional analyses. Our candidate approach focuses on TALE homeodomain (TALE-HD) proteins that specify the identity of distinct gametes. Following fertilization, proteins from distinct TALE-HD subclasses form a heterodimer and translocate to the nucleus to initiate the transition from gametophyte to sporophyte in Chlorophyte algae and Bryophytes. However, whether these genes retain this function in ferns is currently unknown. We are combining our transcriptome atlas with in situ hybridization and phylogenetic analysis to understand the evolution of TALE-HDproteins, andleveraging these new data in ferns to create a comparative framework for understanding gametangia evolution.