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

John C. Cushman热带兰花景天科酸代谢进化起源的机制建议#：0543659被称为景天科酸代谢（CAM）的保水光合作用途径在33个科和328个属中多次进化，占所有维管植物物种的6%以上，使其成为维管植物中第二种最常见的光合作用模式。负责这一重要的光合适应水限制的演变的分子机制是完全未知的。目前的估计表明，在热带兰科（维管植物的最大家族）的20，000种物种中，约有50%表现出CAM光合作用。 在该科中，可以鉴定出没有CAM、弱CAM和强CAM的物种。这些变化可能代表了这种光合途径进化的不同步骤。为了研究这一进化进程，调查将使用碳同位素组成和夜间酸积累映射CAM的发生在一个特定的兰科植物亚科内的一个完善的系统发育。 在CAM中发挥重要作用的特定基因将被选择并用于跟踪基因家族内DNA序列水平的变化以及控制基因表达的基因部分，这可能解释CAM的进化。此外，将利用DNA微阵列技术对基因表达变化进行更大规模的调查。这项研究将为环境变化如何影响CAM未来的分布模式和进化选择提供新的见解。该项目将为有兴趣了解系统发育关系和适应性光合机制发生的本科生和研究生提供独特的实践培训机会。此外，还将在教育机构和公共场所举办热带兰花展览，开展社区外联活动，让学生和公众了解兰花生态生理多样性的重要性以及热带雨林在全球气候变化中发挥的更大作用。

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.