Date of Award

5-2010

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Susan Brawley

Second Committee Member

Arthur C. Grossman

Third Committee Member

Mary Rumpho-Kennedy

Abstract

Porphyra umbilicalis normally reproduces on the Maine coast (U.S.A.) via an asexual pathway that produces neutral spores. The neutral spores develop within sporangia on the blade margin; each sporangium matures to contain 16 spores (2 x 2 in surface view and x 4 in transverse section) along the blade margin. This differs from the dioecious (sexual), heteromorphic life history found in the northeastern Atlantic. It is not known whether sexual reproduction is too rare to be observed, is suppressed, or is lost in the Maine population. The U.S. Department of Energy's Joint Genome Institute (JGI) is currently sequencing the complete nuclear genome of an asexual haplotype (P.uml) of P. umbilicalis from the Maine shore. I describe here the isolation and culture of haplotype P.uml in the laboratory. I have established a 4.5 month generation time for the genomic haplotype in normal laboratory conditions (15 °C, 14:10 L:D, 60 umol photons m-2 s-1). An antibiotic trial was conducted to determine the resistance of neutral spores to antibiotics as a first step in development of a transformation system for P. umbilicalis. Germination of neutral spores was reduced to 1% with 800 mg L-1 geneticin, which suggests that gene inserts with geneticin resistance can be identified in future transformation studies. In a population study using amplified fragment length polymorphisms, I characterized the genetic diversity of P. umbilicalis at two locations in Maine, compared the genetic data to a known sexual population in England, and demonstrated that P. umbilicalis in Maine is not derived from a single clone. Finally, expressed sequence tags (ESTs) generated as part of the JGI genome sequencing project were investigated for genes that are differentially expressed during asexual reproduction. Genes associated with transcriptional regulation, cell signaling, and cell wall modification are upregulated during asexual determination as compared to vegetative growth. The upcoming genome sequence for P. umbilicalis will allow for a more thorough exploration of how asexual reproduction functions in this red algal species.

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