The ability to sense and respond to changes in ambient light conditions is critical to maximizing photosynthetic efficiency and survival in cyanobacteria. One of the best studied examples of these responses is the process of complementary chromatic acclimation (CCA) in the freshwater, filamentous cyanobacterium Fremyella diplosiphon. During CCA the composition of light harvesting antennae complexes reversibly switches between red light-absorbing phycocyanin under red light conditions, to green light-absorbing phycoerythrin under green light conditions. Two separate photosensory systems control CCA, the Rca and Cgi systems. The Rca system controls induction of red light-induced genes and has an inhibitory effect upon green light-induced genes during growth in red light. The Cgi system controls only the green light-induced genes. The mechanism by which these systems regulate genes expressed in green light remained unknown for a number of years. Previously it had been shown that a protein encoded within the cpeC operon, CpeR, was both necessary and sufficient for the induction of other green-light induced genes. Regulation of cpeC could thus be a critical checkpoint during CCA, with two sensory systems integrating to control green light expressed genes. My studies show that the Rca system represses transcription of cpeC in red light through binding of the transcription factor at the end of this pathway to a promoter element called the L Box that can act as both an activator of red light-induced genes and a repressor of cpeC under the same physiological conditions. Further characterization of the L Box demonstrates that its position and orientation within promoters determines its activating or repressing role. My research also demonstrates that the Cgi system represses cpeC post-transcriptionally through its 5' leader under red light, most likely through a transcriptional attenuation mechanism. These findings show that combined transcriptional and post-transcriptional regulation of cpeC by two photosensory systems is a critical step during CCA.
|Advisor:||Kehoe, David M.|
|Commitee:||Fuqua, Clay, Hangarter, Roger, Winkler, Malcolm|
|School Location:||United States -- Indiana|
|Source:||DAI-B 72/03, Dissertation Abstracts International|
|Subjects:||Molecular biology, Microbiology|
|Keywords:||Chromatic adaptation, Cyanobacteria, Fremyella diplosiphon, Phycobilisome|
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