CAREER: Understanding the evolutionary trajectory from C3 to CAM photosynthesis using C3+CAM intermediates

Most plants use an enzyme called Rubisco to take carbon dioxide from the atmosphere and use it to make sugars for growth as a part of photynthesis. Under stressful environmental conditions, Rubisco also interacts with oxygen, which leads to an energetically costly process in plants called photorespiration. Photorespiration reduces plant growth, and plants have repeatedly evolved modifications to the typical photosynthetic pathway to minimize photorespiration. One such photosynthetic modification, Crassulacean acid metabolism (CAM), is found in many dry adapted species and is renowned for providing plants with high drought tolerance, yet little is understood about how CAM has evolved. To clarify the early evolutionary changes associated with CAM evolution, this project studies photosynthetically intermediate species, called C3+CAM, that are representative of plants early in the evolutionary transition to CAM. This research will develop a new screening tool to discover C3+CAM intermediate species, determine how the C3+CAM phenotype is regulated by its environment and by the circadian clock, and help define the genetic mechanisms by which plants evolve CAM photosynthesis. Undergraduates in classroom-based research will screen a large living plant collection to discover new C3+CAM plants. Students also will be trained in classic botany and will learn cutting-edge genomic techniques. The project also will develop freely available educational videos that communicate the importance of the different types of photosynthesis in plants. Crassulacean acid metabolism (CAM) is a modified form of photosynthesis that is hypothesized to have evolved in response to photorespiratory stress in plants, whereby Rubisco fixes O2 instead of CO2. Despite the multiple origins, prevalence, and incredible drought resilience of CAM species, there is limited understanding of how CAM has evolved from a C3 ancestor. Studies focusing on comparing strong, constitutive CAM species to C3 relatives have found large scale changes to the timing and magnitude of gene expression, but they have not been able to determine the evolutionary progression from C3 to CAM. However, several intermediate phenotypes exist along the C3 to CAM spectrum, the so called C3+CAM species. These plants use both pathways to varying degrees, and while they represent a stable phenotype, they also are likely emblematic of intermediate stages of evolution from C3 to CAM. This research focuses on the evolutionary intermediacy of C3+CAM species to 1) develop a novel screening tool using gene expression to better explain and catalog the diversity of C3+CAM vascular plant species; 2) use comparative genomics to determine regulatory changes required to move from C3 to C3+CAM photosynthesis across multiple, independent origins of C3+CAM; 3) determine the role of photorespiration in the evolution of C3+CAM; and 4) involve students in discovering C3+CAM species in a course-based undergraduate research experience (CURE). Educational videos describing photosynthesis from the organismal perspective, rather than the biochemical, will be produced to facilitate and motivate student learning about this fundamental biological process. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2541927 | Program: 01003031DB NSF RESEARCH & RELATED ACTIVIT,01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Karolina Heyduk | Institution: University of Connecticut, STORRS, CT | Award Amount: $1,339,604 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2541927 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2541927.html