DISSERTATION RESEARCH: Evolution of Angiosperm Seed Development: perspectives from Nymphaea thermarum (Nymphaeales)

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Seeds of flowering plants are distinguished by the presence of a novel tissue - endosperm. Endosperm is the product of a second fertilization event, but rather than developing into a second embryo, it becomes a tissue that mediates the relationship between the maternal plant and its compatriot embryo. Endosperm is also an essential part of the human diet: the seeds that provide most of the calories people consume (rice, wheat, corn) consist primarily of endosperm. Studies in model plant species have begun to piece together the mechanisms that control endosperm development, and have revealed that gene imprinting plays an important role. Imprinting occurs when an allele inherited from one parent is silenced. Little scientific attention has been given to how imprinting has evolved in flowering plants. This project will address this discrepancy by analyzing the expression of genes during development of endosperm in the water lily, which is a member of one of the most ancient lineages of flowering plants. While the water lily is uniquely suited to become a model system for the early diverging lineages, it is also on the brink of extinction - making it a compelling case for why exploring and preserving biodiversity is essential for furthering basic scientific research. Analysis of gene expression will be accomplished by creating RNA-seq transcriptomes of key stages during ovule and seed development. From this dataset, two main categories of genes will be targeted for homolog identification: genes that are involved in imprinting-regulation mechanisms and genes that are themselves imprinted. Simple presence/absence of homologs of these genes during seed development in N. thermarum will help to resolve the question of when during angiosperm evolution did these mechanisms became important regulators of endosperm development. In addition, the sampling scheme will make it possible to distinguish suites of gene activity that correlate to specific sets of developmental processes. Finally, the accompanying sequence and expression data will be used to reconstruct the evolutionary history of relevant gene families. This database will represent an important resource for understanding the evolution of angiosperm seeds, and will be made publically available.