Project: EAGER: Diatom Programmed Cell Death at Single-Cell Resolution

NSF Award Abstract:
Diatoms are important primary producers in sunlit oceans and lakes across the globe. They are key players in spring phytoplankton blooms, which in turn support food webs that include productive fisheries. In addition, these photosynthetic diatom cells are known to capture enormous amounts of carbon, which are exported to depth as blooms die off. In oceanic systems, this process effectively removes carbon from the atmosphere for thousands of years. However, the biological mechanisms that lead to carbon sequestration, the transfer of carbon from the atmosphere into the deep ocean, are not well understood. As diatom populations reach the end of the bloom cycle, individual cells start to deteriorate and undergo cell death. The collapse of diatom populations is regarded as a critical point (or tipping point), which can be predicted by understanding the genetic activity of the population. This project seeks to elucidate how environmental change influences diatom cell-death processes. A mechanistic understanding of these cellular processes will elucidate how climate change could alter carbon-removal from the atmosphere and affect ocean productivity. The knowledge and methods developed during this study are applicable across organisms from all domains of life. The broader impacts of this project are focused on high school education and new ideas and approaches for three-dimensional learning opportunities in support of Next Generation Science Standards (NGSS). Specifically, researchers are working with high school educators and partners to teach concepts of systems approaches, tipping points, and carbon sequestration in the marine environment through educational modules.

The goal is to determine the structure of diatom populations during the transition of actively growing cells towards population collapse by identifying the point of commitment (tipping point) at the level of individual cells. The model system is the diatom, Thalassiosira pseudonana, which is widespread and a common bloom-forming species. The random decision process of individual diatom cells is being characterized by establishing a genome-wide gene expression space through the physical and biochemical characterization of the cells. Implementation of the project is focused on measuring the phenotypic responses in the diatom to environmental factors including severe stress. Transcriptomic analyses during the transition of cell proliferation towards culture collapse include bulk (RNA-Seq) and single-cell (scRNA-Seq) high-throughput sequencing. Using a systems biology approach, the genetic information obtained from the samples is incorporated into predictive models to identify genetic transitions that occur prior to population collapse. The systems approach can detect changes in transcriptomic state that precede a critical point in the cell death process leading to predictions of how diatoms respond to environmental change. This work opens new vistas for the elucidation of mechanistic pathways of diatom cell populations.

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.