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 th