Award: OCE-1212392

Phototrophy is the ultimate source of energy that drives the function of a marine ecosystem. Conventionally, the only recognized pathway for sunlight energy to enter the marine ecosystem is photosynthesis thereby phytoplankton and other photosynthetic organisms absorb light and convert a part of its energy to ATP, the energy currency in living organisms. In the early 2000Æs a proton-pump type rhodopsin (PR) was found to occur in marine bacteria living in sunlit ocean surface, challenging the conventional notion. With all-trans retinal as a chromophore PR facilitates transmembrane proton transport creating a proton gradient across the membrane that leads to ATP production. In 2010, we identified genes highly similar to a PR-encoding gene in dinoflagellates, one of the dominant groups of phytoplankton in the coastal ocean, but their function as proton pump has remained to be demonstrated. This project aims at addressing whether PRs from dinoflagellates have the same function as that in bacteria, converting light energy to ATP. Specific objectives included investigations on 1) whether dinoflagellate rhodopsin indeed harvests solar energy and converts it to ATP to promote growth of the host organism; 2) whether rhodopsin has different functions in photosynthetic than heterotrophic dinoflagellates; 3) how widespread this proton-pump rhodopsin is in dinoflagellates. Intellectual merit. In this project, we have found that rhodopsin gene is ubiquitous in dinoflagellates, both in cultured species and in Long Island Sound (LIS), with high sequence diversity. Phylogenetic analyses show that these sequences all belong to proton pump rhodopsin except some sensory type rhodopsin in the heterotrophic dinoflagellate Oxyrrhis marina. We also have observed the expression of the dinoflagellate PR gene in the transformed E. coli in both photosynthetic and heterotrophic dinoflagellates, and detected its light-dependent growth-promoting effect on this bacterium relative to E. coli without this gene. This is evidence that dinoflagellate rhodopsin functions as an energy-generating proton pump. These results suggest that light energy acquiring mechanism independent of photosynthetic apparatus occur not only in bacteria but also in eukaryotic phytoplankton such as dinoflagellates. Our result also suggest that more research efforts should be invested in the future to systematically investigate the ecological significance of this gene in the marine ecosystem. Broader impact. This study has provided essential information for understanding the extent to which eukaryotic rhodopsin may contribute to marine phototrophy. The role of eukaryotic rhodopsin in marine photoheterotrophy and photoautotrophy can begin to be understood. A dataset has been generated for rhodopsin in marine dinoflagellates that will prove valuable for future research. Besides, this project has lent itself to an opportunity for a graduate class (MARN5015: Molecular Approaches to Biological Oceanography) to engage in a real research question. This course consists of a lecture and a laboratory session each week. Because it is a technique-oriented, hands-on intensive course, students are required to conduct a research project and complete a project report at the end. The PI has guided the class to use Rhodopsin as the example gene, and the prevalence and diversity of this gene in Long Island Sound dinoflagellate assemblages as their project topic. They have learned from DNA extraction, PCR, gene cloning and sequencing, to bioinformatics analyses, raising the studentsÆ interest in science. This project also has provided financial support for two graduate students, who have been trained in phytoplankton molecular ecology research. Last Modified: 04/26/2015 Submitted by: Senjie Lin