Date of Award

12-14-2015

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

James T. Morris

Abstract

“Brown marsh” or “sudden marsh dieback” refers to the rapid death of patches varying in size of Spartina alterniflora. In 2000 following a 100-year record drought, approximately 8,000 hectares of S. alterniflora died along the Louisiana coast, which prompted Louisiana Governor Foster to declare a state of emergency. Other cases have been documented at North Inlet, SC as well as various other marshes along the southeastern United States. Currently, there is much dispute regarding the cause of “sudden marsh dieback” but environmental stress is one of the acknowledged constants across sites. We hypothesized an alternative mechanism in which methylation of the genome increases with plant age, reducing stress tolerance. DNA methylation occurs on the cytosine nucleotide and is an epigenetic modification that is crucial for stable gene regulation along with silencing of harmful transposable and repetitive elements (TE and RE respectively) in the plant genome. This modification is initiated and maintained through different pathways and methyltransferase families, but only one family of methyltransferases can propagate and maintain DNA methylation through a process denoted as de novo style methylation. The primary focus of this study was to assess the level of global DNA methylation among Spartina alterniflora clones of variable age at North Inlet, South Carolina through a field survey of separate locations. After completing the field survey, a greenhouse study was conducted in an attempt to ascertain the effect of an environmental stress, increasing salinity, on global DNA methylation. Finally, four isolated genets were located in the field and sampled to test the hypothesis of increasing global methylation with age within each genet. Our results show that although increasing environmental stress does impact survivorship, global methylation rates remain unaffected. This conclusion does not invalidate DNA methylation as a proposed mechanism for the brown marsh event; in fact it correlates with the gene-body methylation phenomena seen throughout various plant species in which a gene actively functions despite being heavily methylated. To further consider DNA methylation as a mechanism for brown marsh, it would be advantageous to look at individual genes, specifically those use for stress and defensive purposes, and their methylation status.

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