This research investigates signaling mechanisms controlling bacterial light responses. Using molecular, biochemical, and genetic approaches, it analyzes how the cyanobacterium Fremyella diplosiphon uses chromatic adaptation to respond to changes in ambient light color. During chromatic adaptation, this photosynthetic organism's light harvesting antennae are restructured. This acclimation process is reversible and allows cells to efficiently use the predominant light wavelength(s) in the environment for photosynthesis. Chromatic adaptation controls transcription of red and green light responsive genes. Recently, a 28 basepair region of DNA called the "R Box" was found near both red and green light responsive genes, suggesting that this sequence is required for coordination of red and green light expression. This research will test the role of the R Box in the regulation of light-responsive genes. Chromatic adaptation is known to be controlled by two photosensory systems. The Rca (regulator for chromatic adaptation) system appears to be a complex phosphorelay that controls the expression of red and green light responsive genes and includes a large response regulator called RcaC. RcaC abundance differs in cells grown in red and green light. This research will determine if RcaC abundance is regulated transcriptionally, translationally, or proteolytically. The second regulatory system, the Cgi (control of green light induction) system, regulates green light induced genes and is uncharacterized. This project will use transposon mutagenesis to generate potential Cgi system mutants and identify genes encoding components of this pathway. These findings will contribute broadly to understanding of bacterial signal transduction systems and plant signaling pathways.
