The coordination of apo-protein and bilin biosynthetic enzyme expression in response to light color and sulfur availability in Fremyella diplosiphon

Fremyella diplosiphon is a freshwater filamentous cyanobacterium that has the ability to dramatically change its color in response to different wavelengths of light in its environment. In red light cells become green and in green light they become red. This process, which is believed to be an acclimation response, has been studied for more than a century and is termed C&barbelow;omplementary C&barbelow;hromatic A&barbelow;daptation (CCA). It involves shifts in the protein composition of the macromolecular light harvesting complexes of cyanobacteria known as the phycobilisomes. These brilliantly colored structures are composed predominantly of proteins, known as phycobiliproteins, which bind linear tetrapyrrole chromophores to gain their specific light harvesting capabilities. I have identified the biosynthetic enzymes involved in the production of the different chromophores produced during CCA and have found that the production of these enzymes themselves is under the control of CCA. My characterization of their expression has provided insight into the processes of light sensing and signal transduction.;Although light is a critical environmental parameter for photosynthetic organisms such as F. diplosiphon, it is not the only cue to which they respond. The availability of nutrients in the environment also has a dramatic effect on the pigmentation of this cyanobacterium. The deprivation of sulfur, in particular, causes another dramatic shift in phycobilisome composition and pigmentation. I have begun to explore the molecular mechanisms of this shift and how it is integrated with CCA. Using RNA blot analysis and reporter fusion assays, I have found that both transcriptional and post-transcriptional mechanisms are involved in controlling the low sulfur phenotype.