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Abstract Detail


Molecular Ecology and Evolution

Silvera, Katia [1], Whitten, W. M. [2], Williams, N. H. [3], Neubig, K. M. [4], Winter, Klaus [5], Cushman, John C. [1].

Evolution of Crassulacean Acid Metabolism in Neotropical Orchids.

Crassulacean Acid Metabolism (CAM) is a water-conserving mode of photosynthesis present in 7% of vascular plant species. The molecular mechanisms responsible for the evolution of this important photosynthetic adaptation to water-limitation are completely uncharacterized. We used stable carbon isotopic composition from leaf samples to determine if photosynthetic carbon assimilation occurs predominantly by the C3 photosynthesis or CAM pathways. Carbon isotopic composition of leaf material of 900 orchid species showed a bimodal distribution with most species exhibiting peak values near -27, suggesting a C3 photosynthetic pathway, or around -15, suggesting a CAM pathway. Titratable acidity measurements of species within the C3 photosynthesis peak revealed species with a weak CAM capacity. When overlain onto a molecular phylogeny of orchids, the distribution of photosynthetic pathways showed that C3 photosynthesis is the ancestral state and that CAM has evolved more than once within the Orchidaceae. High quality leaf RNA samples has been obtained from closely related orchid species from the Subtribe Oncidiinae with a range of photosynthetic pathways from C3 photosynthesis to weak to strong CAM, and the mRNA abundance of molecular markers diagnostic for CAM has been analyzed. An analysis of PEPC gene family structure and mRNA relative abundance showed that at least five isoforms are present in orchids, with one putative CAM-specific PEPC isogene identified in CAM and weak CAM species based on cDNA clone sampling. This interdisciplinary project integrates ecophysiological, biochemical and molecular genetic approaches to understand the evolutionary origins of CAM within the context of a highly resolved phylogeny of orchids.


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1 - University of Nevada, Reno, Department of Biochemistry & Molecular Biology, MS 200, Reno, Nevada, 89557-0014, USA
2 - University of Florida, Florida Museum of Natural History, Gainesville, Florida, 32611-7800, USA
3 - University of Florida, Department of Botany, Florida Museum of Natural History, P.O. Box 117800, Gainesville, Florida, 32611-7800, USA
4 - University of Florida, Department of Botany, 220 Bartram Hall, P.O. Box 118526, Gainesville, Florida, 32611-8526, USA
5 - Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Ancón, Republic of Panama

Keywords:
Crassulacean acid metabolism (CAM)
Orchidaceae
Photosynthesis
Isotopes
Phosphoenolpyruvate carboxylase.

Presentation Type: Oral Paper:Papers for Topics
Session: CP53
Location: Boulevard B/Hilton
Date: Wednesday, July 11th, 2007
Time: 1:00 PM
Number: CP53015
Abstract ID:1952


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