PYI: Evolutionary History of Double Fertilization and the Endosperm

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The evolutionary history of double fertilization and endosperm, two of the most important reproductive features associated with the origin and success of flowering plants will be examined. The developmental fate of the second fertilization in the genus Ephedra, a non-flowering seed plant and a basal member of the most closely related extant group of plants (Gnetales) to the angiosperms, will be studied. The ultimate goal of this work is to determine whether the second fertilization product in Ephedra exhibits endosperm-like qualities that would support a new hypothesis for a pre-flowering plant origin of endosperm. Evidential support for this hypothesis would fundamentally alter our current concepts of the evolutionary history and origins of flowering plants. A second set of studies will examine mate choice in non- flowering seed plants. Although more than fifty percent of flowering plant species exhibit some type of genetic incompatibility mechanism that prevents the fertilization of ovules by pollen from closely related individuals, evidence for similar incompatibility systems among non-flowering seed plants, is rare. Initial studies using Douglas fir have, for the first time, documented pre-zygotic response to pollen quality outside of flowering plants. Planned studies will examine the competitive effects of mixed genetic loads of pollen (and female response to the genetic constitution of pollen) in loblolly pine, a major forestry crop in the southeastern US.