Patterns and Mechanisms of Ovule Diversification

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As the developmental precursors to seeds, ovules are a defining feature ofseed plants and play essential roles in their sexual reproduction. Amongangiosperms, the dominant group of seed plants, ovules are diverse,exhibiting differences in the number of integuments (external sheathingstructures), and in the orientation of the micropyle (the opening in theinteguments which facilitates fertilization). Ovule diversity has beeninvaluable in evolutionary studies of angiosperms, and ovule developmenthas become a useful model for studies on genetic regulation of plantmorphogenesis. An interdisciplinary approach will be used to characterize the historicalpatterns of ovule evolution and its molecular genetic basis. Ovulecharacteristics will be plotted onto the best available phylogenies forangiosperms to clarify transitions between primitive and derived ovulefeatures. Species having either primitive or derived ovule features willbe selected for phenotypic and molecular genetic characterization.Molecular genetic analysis of the basis of changes in integument number andmicropyle orientation will be accomplished through analysis of orthologs ofINO, a gene which regulates these processes in Arabidopsis and which isspecifically expressed in the outer integument. Isolation of INO orthologsfrom key species, and characterization of expression patterns, will enablethe formulation and testing of hypotheses on the molecular genetic changesunderlying ovule diversification. To facilitate future studies on ovule diversification, we will also isolateATS, a gene required for developmental separation of outer and innerinteguments in Arabidopsis. Completion of the proposed work will provide insights into the regulationof plant development, ovule diversification, and their interrelationship.