Genes involved in asexual sporophyte development in Ceratopteris richardii and Arabidopsis thaliana

The life cycle of land plants involves cycling between two multicellular phases, the haploid gametophyte and the diploid sporophtye. Asexual reproductive strategies, that bypass meiosis and fertilization, have evolved in many plants representing diverse taxa among the land plant phylogeny. Apogamy is an asexual reproductive strategy that produces a sporophyte directly from a gametophyte cell without the usual ploidy change associated with syngamy. The genes that drive the process of apogamy are almost completely unknown. Knowledge of these genes and their functions will provide insight into the evolution of asexual reproduction, and has the potential to provide insight into the evolution aspect of the development of the sporophyte body and the alternation of generations in land plants, two very important questions in plant science. My Ph. D. research has focused on elucidating the genes that are involved in the process of apogamy, and understanding the functions of the homologues of these genes in angiosperms. First, I induced apogamy experimentally from the semi-aquatic fern Ceratopteris richardii by culturing them on 2.5% glucose. I discovered that C. richardii gametophytes begin to become committed to the production of apogamous sporophytes after 10 days of culture on glucose. I then created a normalized, subtracted cDNA library that represents genes that increase in transcription in gametophytes during this commitment time. By comparing the Gene Ontology terms mapped to this cDNA library with that of the gametophyte transcriptome of the homosporous fern Pteridium aquilinum, I discovered that the C. richardii apogamy library is enriched in genes that are involved in stress response and metabolism. The C. richardii apogamy library also contains many sequences whose homologues in Arabidopsis are specifically expressed or upregulated in flower organs or seed structures, both of which are absent in ferns. One of these genes, UNC93-like, is also expressed in the eggs of C. richardii gametophytes, as evidenced by