Reproduction by gamete fusion is the norm in the biological world; however, non-fusion reproduction occurs widely, including among land plants. If harnessed, non-fusion production of seeds will change the way hybrid seeds, such as corn, are currently made in agriculture. In order to understand the mechanisms of non-fusion reproduction, we propose to first understand how non-fusion embryos are formed in a simpler group of plants - ferns. Ferns are non-seed plants that lack the storage part of a seed but nonetheless form an embryo as the result of a sperm fertilizing an egg (fusion). The salient feature of a fern is having the sperm and egg producing parts of the plant housed in a tiny, free-living entity independent of the mother plants. Therefore this tiny, simple, green entity provides a rare opportunity to study the mechanisms of fusion reproduction, and important to this project, the non-fusion formation of an embryo without fertilization. Using this system, the genes key to non-fusion reproduction will be identified and their functions in this process tested. This research program will emphasize the identification and training of talented female scientists and data from the proposed research will be used in an undergraduate course.
Normally performing the essential roles of gamete formation and fertilization, the macroscopic gametophytes can also be coaxed to produce sporophytes without fertilization, a process called apogamy. In the reverse process, apospory, sporophytes can be made to produce gametophytes without meiosis. With apogamy and apospory, ferns can exhibit non-fusion alternation of the sporophyte and the gametophyte generations. This level of plasticity alternating between the two generations is not seen in seed plants. Thus, the apogamy and apospory of ferns offer an ideal system to answer the question that lies at the heart of non-fusion reproduction: Which genes control the developmental pathways leading to the gametophyte or the sporophyte generations? It is hypothesized that many genes that control fusion reproduction in ferns and seed plants are conserved and non-fusion reproduction in land plants has arisen by altering these genes. Furthermore, the non-fusion alternation of generations through apogamy and apospory in the model fern C. richardii occurs by altered regulation of a set of genes that normally are reserved for initiating embryogenesis from a zygote and gametogenesis from a spore, respectively. The research team has built up necessary technology and materials including apogamy induction, stable gene transfer, C. richardii transcriptome, and whole mount in situ methods. These will be used to achieve the goal of identifying key genes and gene networks involved in apogamy and apospory in the model fern C. richardii with the following specific aims: Studying the role of the candidate genes in fusion/non-fusion alternation of generations in C. richardii, gene discovery for apogamy and apospory in C. richardii, and functional analysis of newly discovered genes that are predicted to act in non-fusion alternation of generations in C. richardii.
