Redox and Light Derived Mechanisms of Environmental Perception are Utilized for Regulation of the Cyanobacterial RNA Helicase crhR

  • Author / Creator
    Ritter, Sean
  • Cyanobacteria occur worldwide in environments that contain water and sunlight. They are crucial, positive players in carbon, oxygen and nitrogen cycling and function as producers of biosynthetic products such as biofuels. To optimize these processes, understanding mechanisms by which cyanobacteria sense environmental signals and regulate cellular processes is essential. Cyanobacteria obtain all of their energy from photosynthetic light harvesting. As such, the ability to genetically sense and respond to changes in their environment is essential for survival. In bacteria, environmental sensing normally proceeds through stress-specific two- component signaling pathways. Despite the fact that the model cyanobacterial species, Synechocystis, encodes numerous stress specific two-component systems, a number of stress responsive genes are not regulated by any of these identified systems. Here, regulation of one of these orphan genes, the DEAD-box RNA helicase crhR, is described. Extensive evidence for an unexpected mechanism, by which divergent abiotic stresses are all sensed by their common effect on the redox potential of the photosynthetic electron transport chain, is provided. The convergent sensing mechanism fits the lifestyle of Synechocystis, allowing rapid and concerted changes in gene expression in response to a diverse abiotic stress. In addition, expression of crhR is demonstrated to be responsive to multiple distinct light regulated mechanisms at the transcriptional, translational and proteolytic levels, further supporting a crucial role for crhR in regulation of photosynthesis. Finally, the specific site of the electron transport chain and the downstream signal transduction components which link changes in redox poise with altered gene expression were investigated. The redox status of QB, a fixed stable quinone within photosystem II, and not freely diffusible plastoquinone, is the specific site of physiological change which facilitates redox regulation of crhR. Evidence for involvement of the hik8/rpaA/rpaB two- component signaling system in regulation of crhR is also provided. Hik8 has been demonstrated to function downstream of the KaiABC circadian oscillator complex in Synechocystis, suggesting implications of the circadian clock in regulation of crhR expression. On an evolutionary scale, evidence for related systems in Staphylococcus aureus and plant chloroplasts suggests that convergent sensing mechanisms may occur more widely than anticipated.

  • Subjects / Keywords
  • Graduation date
    Spring 2020
  • Type of Item
  • Degree
    Master of Science
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