Photosynthesis is a basic process supporting the vast majority of life on Earth. However, for plants living under water-limited conditions, photosynthetic productivity can be reduced by hotter and drier climatic conditions. To counteract these conditions, some plants utilize forms of photosynthesis that increase the efficiency with which they use water. One such innovation seen in plants that grow in deserts or other water-limited habitats is referred to as CAM (Crassulacean Acid Metabolism). The CAM innovation is found in a large number of diverse plant lineages and typically associated with stem (e.g. cacti) or leaf (e.g. agaves) succulence. The proposed research project will use several approaches to address fundamental questions about how plants use CAM and how genes involved in performing CAM are regulated in response to varying environmental conditions. To achieve this, the project will focus on the independent evolution of CAM in the orchid and agave plant families, both of which have species known for their ability to thrive in water-limited environments. This research will provide a foundation for understanding the genetic basis of CAM pathways and potentially transfer to economically important plants for improved water use efficiency under drought conditions leading to improved productivity. Additionally, this project would result in the training of undergraduate and graduate students, including individuals from under-represented groups. There are also plans to integrate the results of the project into classroom learning and broader outreach activities.
This project utilizes an integrated research program on two instances of CAM photosynthesis to illuminate the mechanisms that link ecological, genetic and molecular dimensions of the evolutionary processes that contribute to the origin and maintenance of biodiversity. Photosynthesis is a fundamental process supporting biodiversity in the vast majority of ecological communities on our planet, while at the same time a physiological challenge for primary producers living under water-limited conditions. The evolutionary history of photosynthetic organisms has included repeated origins of carbon concentrating mechanisms that increase water-use efficiency and productivity in extreme environmental conditions. Crassulacean acid metabolism is one such innovation that has facilitated diversification of vascular plant lineages in an array of habitats. The proposed project will integrate ecological, physiological, phylogenetic, genetic and genomic approaches to address fundamental questions about how plants use CAM and how genes involved in performing CAM are regulated in response to different environmental conditions. The study systems for this project are the species-rich Agavoideae (Asparagaceae) and Oncidiinae (Orchidaceae) lineages, both of which include CAM, C3 (typical form of photosynthesis) and facultative or weak CAM species. These systems will aid in inferring the phylogenetic and environmental context for multiple gains and losses of CAM photosynthesis in both lineages. Comparative analyses of RNA will illuminate the interacting molecular and environmental drivers of shifts between C3 and CAM photosynthesis and the impact of these shifts on the origin and maintenance of species diversity. Furthermore, shifts in gene function associated with the gain and loss of CAM will be tested through genetic analyses of a yucca hybrid, resulting from a natural cross between a CAM and C3 parental species, and experimental manipulations of gene expression in the emerging orchid model species, Erycina pusilla (Oncidiinae).
