AuthorDilkes, Brian R.
AdvisorLarkins, Brian A.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractDuring maize endosperm development, the cell cycle in the majority of cells switches from a mitotic to an endoreduplication cell cycle. This results in cells of varying ploidies within the tissue, and is presumed to be a factor in its rapid growth. Investigating the inheritance of variation in endoreduplication in maize endosperm will begin to elucidate the genetic mechanisms controlling it. It has been hypothesized that retinoblastoma-related proteins (RRBs) negatively regulate the G1/S transition during both mitotic and endoreduplication cell cycles. Testing this hypothesis in both mitotic cells and endoreduplicating endosperm cells will further our understanding of the molecular mechanisms regulating endoreduplication. Flow cytometry was used to assess the variability of endoreduplication in endosperms of maize inbred lines. High levels of endoreduplication were observed in popcorns relative to Midwestern dent corns. To study the genetic regulation of endoreduplication, four inbreds were crossed to B73 and developing endosperms from parental, reciprocal F1, and backcross generations were subjected to flow cytometric analysis. Maternal zygotic effects, often considered a form of parental imprinting, and maternal sporophytic effects were detected. To test the feasibility of introgressing a high endoreduplication phenotype into a Midwestern dent inbred line, a backcross population was generated using B73 as the reciprocal parent and the popcorn Sg18. The heritabilities calculated from an analysis of the backcross population generally agree with the values calculated in the larger crossing experiments. The Wheat Dwarf Virus RepA protein binds RRBs and is predicted to activate the cell cycle. RepA and the maize RRB, ZmRb1, were tested for cell cycle regulatory activity in tobacco BY-2 cells and determined to be an activator and repressor, respectively. The effect of RepA on endoreduplication was evaluated in both mitotically-active maize callus cultures and developing endosperms. Flow cytometric measurements of nuclear ploidy showed that RepA expression was sufficient to convert a mitotic into an endoreduplication cell cycle in calli but had no discernable effect on endopolyploidy in developing endosperm by 18-days after pollination (DAP).
Degree ProgramGraduate College