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Abstract Detail


Plant-Symbiont Interactions

Rumpho, Mary [1], Worful, Jared [2], Lee, Jungho [3], Kannan, Krishna [4], Soule, Kara [2], Tyler, Mary [5], Manhart, James [6].

The Search for Horizontal Gene Transfer in a Kleptoplastic Sea Slug.

Laboratory culturing confirmed that the sacoglossan mollusc Elysia chlorotica feeds on and subsequently harbors chloroplasts from the heterokont alga Vaucheria litorea. This symbiotic (or kleptoplastic) association sustains the sea slug photoautotrophically for its entire ten month life-cycle in the absence of any additional algal food supply; only light and a source of CO2 are required. The chloroplasts are not heritable and no algal nuclei have been detected within the cells of the mollusc. Sequencing of the 115,341 bp algal chloroplast genome revealed a highly compact genome containing 138 protein, 27 tRNA, and 3 rRNA genes, but it does not contain the minimum repertoire of genes necessary to support photosynthesis in an animal. Horizontal gene transfer (HGT) of algal nuclear genes to the sea slug nuclear and/or mitochondrial genome(s) is a more plausible source for the essential nuclear-encoded chloroplast-targeted proteins. In a targeted HGT discovery approach, we have employed PCR and RT-PCR (V. litorea homologous primers) to demonstrate the presence and expression of two algal nuclear encoded photosynthesis genes, the Calvin Cycle enzyme phosphoribulokinase (prk) and the photosystem II manganese stabilizing protein (MSP, psbO), in sea slug DNA and cDNA and sea slug egg DNA. We have also initiated sequencing of the mtDNA of E. chlorotica eggs to determine if this is a site for HGT insertion. To date, we have obtained sequence for about 3000 bp with high homology to rrnL, nad5, nad6, cox1, and cob. Full analysis of the mitochondrial genome, as well as genome walking results of flanking genomic DNA sequence for both presumptive horizontally transferred genes, will be presented to provide indicative clues as to where and how the foreign DNA was inserted within its new host.


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1 - University of Maine, Biochemistry, Microbiology & Molecular Biology
2 - University of Maine, Biochemistry, Microbiology and Molecular Biology
3 - Seoul National University, Biological Sciences
4 - University of Maine, Biochemistry, Microbiology and Molecular Biology, 5735 Hitchner Hall, Orono, ME, 04469-5735, USA
5 - University of Maine, Biology
6 - Texas A&M University, Biology

Keywords:
Elysia chlorotica
Vaucheria litorea
Symbiosis
kleptoplasty
chloroplast genome
horizontal gene transfer
phosphoribulokinase
psbO
mitochondrial genome
Photosynthesis
heterokont.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P16006
Abstract ID:391


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