Model cyanobacteria have been extensively studied to learn many details of photosynthesis. However, these organisms exhibit more limited physiological responses to light and nutrients than many more complex cyanobacteria, which are often considered to be more difficult to study. The concept behind this project is "to let nature be the guide" to study photosynthesis in stressful settings in situ and to understand those photosynthetic processes identified mechanistically by using laboratory model organisms, genetics, biochemistry and biophysics. By learning more about adaptation and acclimation in cyanobacteria, it should be possible to develop strategies to improve photosynthetic efficiency in crop plants. The recently discovered capacity of some cyanobacteria to use far-red light for oxygenic photosynthesis raises questions about how those cyanobacteria are able to expand their usage of the solar spectrum reaching Earth's surface. This project will use genetic systems that have been developed for non-model cyanobacteria that exhibit diverse adaptive and acclimation responses. Genetic methods, together with physiological, biochemical and biophysical approaches will be used to study the photosynthetic apparatus in these organisms. This proposal offers a unique opportunity to expand knowledge of 'real-world' photosynthesis and is likely to provide new insights for engineering photosynthetic organisms intelligently for human needs, including expanding the light-use capabilities of crop plants. This project will provide training for underrepresented minorities in STEM research and education. The developed photobioreactor concept for the classroom will be used to involve K-12 level students in STEM education.
The defining premise of this project is that terrestrial cyanobacteria have evolved novel adaptive and acclimation responses to optimize light harvesting and energy trapping in environments with strongly filtered (e.g., far-red) light, variable redox states, and the intensive energetic demands of nitrogen fixation. Many cyanobacteria have a cluster of 17 genes encoding core subunits of Photosystem I (PSI), PSII, and phycobilisomes. Combined with the synthesis of chlorophylls (Chls) f and d, the products of these genes confer an acclimation response that permits growth in far-red light (700 to 800 nm), a process known as FaRLiP. This project will use the genetic system developed in Chlorogloeopsis fritschii PCC 9212 to dissect FaRLiP and other postulated acclimation and adaptive responses by determining role of different genes and their variants in acclimation responses of PSI and their roles under anoxic, nitrogen-fixing conditions. This project will also characterize the energy transfer and trapping kinetics in PSI and PSII complexes and study long-wavelength-absorbing phycobiliproteins from cells undergoing FaRLiP and other adaptation/acclimation responses by performing genetic analyses and manipulations, biochemical analyses, mass spectrometry/proteomics, site-specific mutagenesis, biophysical methods (EPR spectroscopy, time-resolved optical spectroscopy). This project is supported by the Molecular Biophysics Cluster of the Molecular and Cellular Biosciences Division in the Directorate for Biological Sciences.
