Chromatic Acclimation: A Novel Transcriptional Control System for Use in Optogenetics

About This Grant

The marine phytoplankton Synechococcus senses and responds to changes in the ratio of blue to green light in its environment. This response, called the Type 4 Chromatic Acclimation (CA4), allows these cells to efficiently adjust their photosynthetic machinery to optimally capture the most abundant of these two light colors. This is important because the amount of blue and green light varies tremendously throughout the ocean and light availability usually limits photosynthesis and growth. Synechococcus is the second most abundant photosynthetic organism in the oceans, where about 50% of the photosynthesis on Earth occurs. Therefore, studying CA4 will provide important insights into the regulation of photosynthesis on our planet. In addition, CA4 appears to be sensing light color through completely novel photoreceptors. This project characterizes these CA4 elements and the mechanisms through which they work, providing basic understanding for the application of important new components in Biotechnology, specifically in Synthetic Biology and Optogenetics. An understanding of the mechanisms of the CA4 elements could lead to improved process control by blue and green light during industrial processes. This project contains activities to encourage high school students to enter STEM disciplines and integrates education and research through the participation of high school teachers and students. This project's goal is to define the regulatory mechanisms controlling changes in the photosynthetic light harvesting antennae of the phytoplankton Synechococcus spp., the second most abundant photosynthetic marine organism. This process, called Type 4 Chromatic Acclimation (CA4), allows cells to sense the ratio of blue to green light and alter the transcriptional activity of specific genes. Two approaches will be used to define this regulatory system. First, light-sensing chromophores associated with the two putative, novel photoreceptors FciA and FciB will be identified by purifying epitope-tagged versions from CRISPR transformed Synechococcus cells and analyzing them using spectroscopy and mass spectrometry. Second, the CA4-responsive DNA binding sites of CA4-regulated genes will be identified by joining their upstream regions to reporter genes and replacing specific DNA sequences of these regions, then introducing these genes into Synechococcus to identify CA4 control elements. DNA binding by FciA and FciB, which are also putative transcription factors, will be examined in blue and green light using ChIP-seq and DNA footprinting. These AraC family proteins are likely the first of a new photoreceptor class. The CA4 blue-green light regulatory system will be potentially valuable for use in Systems Biology and Optogenetics. 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.