Cell Biology & Molecular Genetics Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2750
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Item Shaping the Dicot Fruit: Molecular and Genomic Approaches to Fruit Development(2016) Hawkins, Charles; Liu, Zhongchi; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The fruit is one of the most complex and important structures produced by flowering plants, and understanding the development and maturation process of fruits in different angiosperm species with diverse fruit structures is of immense interest. In the work presented here, molecular genetics and genomic analysis are used to explore the processes that form the fruit in two species: The model organism Arabidopsis and the diploid strawberry Fragaria vesca. One important basic question concerns the molecular genetic basis of fruit patterning. A long-standing model of Arabidopsis fruit (the gynoecium) patterning holds that auxin produced at the apex diffuses downward, forming a gradient that provides apical-basal positional information to specify different tissue types along the gynoecium’s length. The proposed gradient, however, has never been observed and the model appears inconsistent with a number of observations. I present a new, alternative model, wherein auxin acts to establish the adaxial-abaxial domains of the carpel primordia, which then ensures proper development of the final gynoecium. A second project utilizes genomics to identify genes that regulate fruit color by analyzing the genome sequences of Fragaria vesca, a species of wild strawberry. Shared and distinct SNPs among three F. vesca accessions were identified, providing a foundation for locating candidate mutations underlying phenotypic variations among different F. vesca accessions. Through systematic analysis of relevant SNP variants, a candidate SNP in FveMYB10 was identified that may underlie the fruit color in the yellow-fruited accessions, which was subsequently confirmed by functional assays. Our lab has previously generated extensive RNA-sequencing data that depict genome-scale gene expression profiles in F. vesca fruit and flower tissues at different developmental stages. To enhance the accessibility of this dataset, the web-based eFP software was adapted for this dataset, allowing visualization of gene expression in any tissues by user-initiated queries. Together, this thesis work proposes a well-supported new model of fruit patterning in Arabidopsis and provides further resources for F. vesca, including genome-wide variant lists and the ability to visualize gene expression. This work will facilitate future work linking traits of economic importance to specific genes and gaining novel insights into fruit patterning and development.Item The role of auxin on the evolution of embryo development and axis formation in land plants(2005-03-10) Poli, DorothyBelle; Cooke, Todd J.; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)ABSTRACT Title of Dissertation: THE ROLE OF AUXIN ON THE EVOLUTION OF EMBRYO DEVELOPMENT AND AXIS FORMATION IN LAND PLANTS DorothyBelle Poli, Doctor of Philosophy, 2005 Dissertation directed by: Professor Todd J. Cooke, Cell Biology and Molecular Genetics This thesis examined the role of auxin in the evolution of land plants. Several approaches were used to study how auxin regulates the development in the bryophyte sporophytes. The altered growth of isolated young sporophytes exposed to applied auxin (indole-3-acetic acid) or an auxin antagonist (p-chlorophenoxyisobutyric acid) suggested that endogenous auxin regulates the rates of axial growth in all bryophyte divisions. In the hornwort Phaeoceros personii, auxin moved at very low fluxes, was insensitive to an auxin-transport inhibitor (N-[1-naphthyl]phthalamic acid), and exhibited a polarity ratio close to 1.0, implying that auxin moves by simple diffusion. The liverwort Pellia epiphylla exhibited somewhat higher auxin fluxes, which were sensitive to transport inhibitors but lacked any measurable polarity. Thus, auxin movement in liverwort sporophytes appears to result from facilitated diffusion. In the moss Polytrichum ohioensis, auxin movement was predominantly basipetal in young sporophytes and occurred at high fluxes exceeding those measured in maize coleoptiles. In older sporophytes, acropetal auxin flux had increased beyond the level measured for basipetal flux in the specimens observed in several, but not all, seasons. The evidence from both inhibitor treatments and isolated tissues is consistent with the interpretation that the cortex carries out basipetal transport in both younger and older sporophytes, whereas the central vascular tissues carries out basipetal transport in younger sporophytes and acropetal flux in older sporophytes. Given the significant differences in fall rainfall in the collection years, the purported sensitivity of vascular tissue development may account for the seasonal variation observed in these experiments. Auxin regulators and polar transport were also used to study the regulation of the embryogenesis of the fern Marsilea vestita. Auxin biosynthesis inhibitors affected initial cell proliferation resulting in the formation of aborted embryos, p-chlorophenoxyisobutyric acid delayed growth and development in all stages of embryogenesis while -naphthaleneacetic acid mediated rapid cell proliferation that caused enlarged disorganized embryos. Polar auxin transport inhibitors caused no significant abnormalities, which suggested a limited role for polar transport in fern embryogenesis. In conclusion, this evidence suggests that auxin is ultimately involved in the establishment of the body plans in all land plant sporophytes.