Signal Transduction Mechanisms Controlling Chromatic Adaptation

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This research investigates signal transduction mechanisms controlling light responses in bacteria. It seeks to uncover how the cyanobacterium Fremyella diplosiphon senses and responds to changes in light color. This process, called "complementary chromatic adaptation" (CCA), involves massive resynthesis of this photosynthetic organism's light harvesting antennae, resulting in a complete color change. This reversible acclimation process allows cells to efficiently use the predominant light wavelength(s) in the environment for photosynthesis. CCA is controlled by two light-responsive pathways that mediate changes in transcription of many genes. The Rca pathway appears to be a complex phosphorelay that controls the expression of red and green light-induced genes and contains three known components, a phytochrome-like photoreceptor and two response regulators. The Cgi pathway controls only green light induced genes. None of the components in this pathway have been isolated. The Rca and Cgi systems may integrate at DNA sequences called "R Boxes" through an OmpR-like control mechanism. These studies will answer fundamental questions concerning the mechanism of CCA regulation. They will determine (i) how red light increases pcyA and cpc2 expression levels through deletion and linker scanning analyses, protein binding and footprinting studies, and purification of CCA transcription factors (ii) how the Cgi and Rca systems regulate cpeCDESTR expression through promoter and R Box deletion analysis and (iii) what components make up the Cgi system by transposon mutagenesis and analysis of putative cgi mutants. Broader impacts include increased understanding of how photosynthetic species acclimate to light and training of members of underrepresented groups in science.