DOI
https://doi.org/10.25772/D7GG-Q964
Defense Date
2013
Document Type
Thesis
Degree Name
Master of Science
Department
Biology
First Advisor
William B. Eggleston Jr.
Abstract
Canalization, the stability of phenotypes in the presence of a specific genotype and environment is important for trait selection and understanding gene expression pathways. The goal of this study was to investigate mechanisms involved in the loss of canalization at the maize r1 locus. A specific lightly colored R-sc derivative, R-sc:86-17(L), was mutagenized with ethyl methyl sulfonate (EMS), and the progeny screened for restoration of dark seed color and canalization. Putative revertants/mutants were mapped relative to the r1 locus, tested for complementation to each other to identify a minimum number of genes involved in canalization, tested for cis silencing of the r1 gene Lc, analyzed to determine the genetic basis for loss of canalization and r1 gene expression, analyzed for changes in molecular structure at the r1 locus, and analyzed for changes in cytosine methylation patterns. At least two complementation groups were found to be responsible for increased seed color, one at or near r1 and one elsewhere in the genome. Phenotypic analysis revealed highly variable kernel pigmentation, possible incomplete penetrance and a novel class termed Nc enhancers. Nc enhancers were characterized by light to heavy mottling. Southern blot hybridization analysis demonstrated that 19 out of 20 putative EMS-induced mutants were unchanged in the molecular structure of genes Sc‖nc1, Nc2, and Nc3. One mutant resulted in the loss of one of the Nc genes. The loss of Lc expression was found to be rare in R-sc:86-17(L) Lc, and restoration of seed color in R-sc:86-17(L)/P heterozygotes was found to have resulted from recombination between Sc‖nc1 and P with loss of Nc2 and Nc3. Analysis of cytosine methylation patterns revealed low levels of methylation in the 5’ region of Sc and high levels in the 5’ region of the Nc genes and in the 3’ ends of Sc‖nc1, Nc2 and Nc3 in the homozygous putative EMS-induced mutants as previously found for R-sc:86-17(L). Four out of the twenty EMS-induced mutants tested displayed altered methylation patterns, with changes at both the 5’ and 3’ regions of the r1 genes. These findings suggest that the genes or elements involved in the canalization and/or restoration of seed color of R-sc are located at the r1 locus, at the 3’ end of the Sc gene and that at least one additional site in the genome is involved in seed color expression of r1.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
August 2013