Mavi ışığın tek hücreli organizmaların transkriptom profiline etkisi

The ability of light perception is crucial for the survival of most organisms that enables them to adjust their physiology and metabolism to the changing environmental conditions. Light, in contrast, is also a threat to any living organism owing to the deleterious effects it can have on nucleic acids, lipids and proteins. Therefore, the capacity to sense and respond to light is widespread among prokaryotes and eukaryotes to survive and adapt themselves as a result of selective pressure of the solar irradiation. This dissertation concentrates on the analysis of light regulated pathways in unicellular organisms, non-phototrophic prokaryote Vibrio cholerae and phototrophic red alga Cyanidioschyzon merolae, via transcriptome profiling. C. merolae is one of the most primitive of photosynthetic eukaryotes. Since it is an extremophile, it is conceivable to study the effect of light on this organism to see how it adapts itself to different environmental conditions and to establish an evolutionary conserved global light response between algae and land plants. Therefore, we decided to investigate the direct effect of red and blue lights at the transcriptional level as well as to verify known blue light receptor genes and the involved transduction pathways using next generation RNA-seq approach. Our results indicated that transcriptional regulations of 35 % of the total genes, including the genes encodes 46 % of transcription factors, were regulated by blue and red lights in C. merolae. Unexpectedly, although there are yet no identified red light photoreceptors, 22 % of the total genes (1116) were regulated by the red light; 521 genes were solely red-light responsive. Transcriptional modulation due to light exposure does not arise from photo-oxidative stress. Blue light dependent regulation of three cryptochromes (CmPHR2, CmPHR3 and CmPHR7) implies a potential role in light-dependent transcriptional regulation in C. merolae. In spite of absences of any red light photoreceptors, a great impact of the red light on the biological processes may suggest the importance of retrograde signaling in this organism. Secondly, we investigated the effect of blue light in non-phototrophic bacteria V. cholerae by using genetics and transcriptome profiling. Genome-wide analysis revealed that the transcription of 6.3% of the genes was regulated by blue light in V. cholerae. To understand signaling mechanisms, we generated several knockout cell lines and subjected to genome-wide analysis under blue light condition. Studies with a double mutant confirm an anti-sigma factor (ChrR) and a novel putative metalloregulatory-like protein (MerR) are responsible for the genome-wide regulation to blue light response in V. cholerae. We further showed that blue light enhances ROS production, possibly generated through the oxidative phosphorylation pathway. These results demonstrate that V. cholerae responds to blue light with a novel mechanism to produce an appropriate response against photo-oxidative stress. This response regulates the transcription of genes involved in cellular protection, DNA repair, and carbon metabolism. Outside its host, V. cholerae can survive for extended periods in natural aquatic environments. Therefore, the regulation of light response for V. cholerae is a critical cellular process for its survival. Collectively, all these data reveal that light is important not only for phototrophs but also non-phototrophs to regulate their metabolism and related physiological pathways through elegant and complex signaling cascades.