Mechanisms of the Evolutionary Origins of Crassulacean Acid Metabolism (CAM) in Tropical Orchids

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John C. CushmanMechanisms of the Evolutionary Origins of Crassulacean Acid Metabolism in Tropical OrchidsProposal #: 0543659The water-conserving photosynthetic pathway known as Crassulacean acid metabolism (CAM) has evolved multiple times in 33 families and 328 genera comprising more than 6% of all vascular plant species making it the second most common mode of photosynthesis among vascular plants. The molecular mechanisms responsible for the evolution of this important photosynthetic adaptation to water-limitation are completely uncharacterized. Current estimates indicate that approximately 50% of the 20,000 species within the tropical orchid family, the largest family of vascular plants, exhibit CAM photosynthesis. Within this family, species that exhibit no CAM, weak CAM, and strong CAM can be identified. These variations may represent different steps in the evolution of this photosynthetic pathway. In order to study this evolutionary progression, surveys will be performed using carbon isotopic composition and nocturnal acid accumulation to map the occurrence of CAM upon a well-established phylogeny within one particular subfamily of orchids. Specific genes that play important roles in CAM will be selected and used to track changes at the DNA sequence level within gene families and the portions of genes that control how the genes are expressed, which might account for the evolution of CAM. In addition, larger surveys of gene expression changes will be undertaken using DNA microarray technology. This research will provide novel insights into how environmental changes might impact future distribution patterns and evolutionary selection of CAM. This project will provide unique hands-on training opportunities for undergraduate and graduate students interested in learning about phylogenetic relationships and the occurrence of adaptive photosynthetic mechanisms. In addition, an exhibit of tropical orchids will be developed and displayed at educational institutions and public venues to conduct community outreach to inform students and the general public about the importance of ecophysiological diversity of orchids and the larger role that tropical rain forests play in global climate change.