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Abstract Detail

Molecular Ecology and Evolution

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

Evolution of Crassulacean Acid Metabolism in neotropical orchids: linking isotopes, genetic expression and habitat preference.

CRASSULACEAN Acid Metabolism (CAM) is a water-conserving mode of photosynthesis present in more than 6% of vascular plant species. The molecular mechanisms responsible for the evolution of this important photosynthetic adaptation to water-limitation are completely uncharacterized. 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. Stable carbon isotopic composition was measured for over 900 neotropical orchid species to determine if photosynthetic carbon assimilation occurs predominantly by the C3 photosynthesis or CAM pathways. Carbon isotopic composition of leaf material 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 Orchidaceae. High quality RNA samples have been obtained from ten orchid species from subtribe Oncidiinae with a range of photosynthetic pathways from C3 photosynthesis to weak or strong CAM, and the mRNA abundance of molecular markers diagnostic for CAM (e.g., PEPC, PPCK, CAH and GPT) have been analyzed. This analysis is part of a larger project in which approximately 1600 species will be analyzed from living and preserved specimens for a greater understanding of the evolutionary origins of photosynthetic pathways in orchids. This work is supported by NSF grant IOB-0543659.[c.e.:srb]

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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 - Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Ancón, , Republic of Panama

Crassulacean Acid Metabolism
carbon isotopes
gene expression

Presentation Type: Poster:Posters for Topics
Session: 48-89
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM
Abstract ID:423

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