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Abstract Detail


Systematics Section / ASPT

Barrett, Craig F. [1], Freudenstein, John [2].

Evolution of the photosynthesis gene rbcL in a mycoheterotrophic genus Corallorhiza Gagnebin.

FULL-MYCOHETEROTROPHY has arisen independently at least ten times in the Orchidaceae, more than in any other plant family. Fully mycoheterotrophic plants are parasites in a tripartite symbiosis between autotrophic plants and mycorrhizal fungi. Corallorhiza spp. display “symptoms” of full-mycoheterotrophy, including leaf/root reduction, loss of green pigmentation (excluding C. trifida), and symbiotic shifts onto mycorrhizal fungi not often associated with closely related plant taxa. The purpose of this study was to analyze the consequences of full-mycoheterotrophy on a crucial photosynthesis gene, rbcL (RuBisCO Large Subunit). We sequenced the 1 428 bp RuBisCO Large Subunit gene in representatives of eight species of Corallorhiza. Our findings suggest that at least one species, C. striata (n=3 accessions), has undergone pseudogene formation. This is evidenced by a downstream stop codon (UGA) directly adjacent to rbcL’s start codon (AUG), a two base insertion in its 5’ region, and an eight base deletion in its 3’ region. rbcL pseudogene formation is likely the result of relaxed purifying natural selection on RuBisCO’s function; the necessity to fix carbon dioxide and form photosynthate has been obviated by the ability to derive all carbon indirectly from other autotrophs via a fungal connection, allowing accumulation of indels and nonsynonymous substitutions. This finding is in accordance with similar results reported from the holoparasitic Orobanchaceae, and is the first of its kind for the >400 fully mycoheterotrophic species in the plant kingdom.


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1 - Ohio State University, Department of Evolution, Ecology, and Organismal Biology, OSU Herbarium (OS), Museum of Biological Diversity, 1315 Kinnear Rd., Columbus, Ohio, 43212, USA
2 - Ohio State University, Department of Evolution, Ecology and Organismal Biology, Museum of Biological Diversity, 1315 Kinnear Rd., Columbus, Ohio, 43212, USA

Keywords:
Corallorhiza
rbcL
molecular evolution
Pseudogene
RuBisCO
mycoheterotrophy
Purifying Selection.

Presentation Type: Poster:Posters for Sections
Session: 48-154
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM
Abstract ID:393


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