Degree
Doctor of Philosophy (PhD)
Department
Biological Sciences
Document Type
Dissertation
Abstract
Photosynthesis sustains the majority of life on Earth by converting light energy into chemical energy. Photosystem II plays a crucial role in initiating this process by capturing and transforming light energy into a form that can eventually be stored as chemical energy. The biogenesis and repair of PSII are intricate processes involving multiple components. Many accessory factor proteins are essential to carry out the de novo PSII assembly and repair. PratA is one of the accessory factor proteins that has been previously characterized. We aimed to better study the effects of knocking out PratA in Synechocystis 6803. Multiple mutants from the same transformation screen were identified to have differences in phenotype when PratA was knocked out. Using Sequencing techniques, we confirmed the presence of secondary mutations in psbB (encodes CP47) in multiple ΔpratA lines. Characterization of the ΔpratA mutant line without any secondary mutations in psbB revealed that PratA is not a required accessory protein for PSII assembly. Characterization of the ΔpratA mutant lines with severe mutations in CP47 (affecting transmembrane helices) showed reduced PSII activity and stability, and complementation with pratA didn’t have much of an effect. Characterization of the ΔpratA mutant lines with less severe mutations in CP47 (affecting the lumenal loop) also showed reduced PSII activity and stability, but complementation with pratA rescued the phenotypes to a greater extent. We showed that PratA is able to perform a supportive role when the PSII is moderately defective.
PSII uses light energy to oxidize water and reduce plastoquinone (PQ). The PQ pool is one of the major components of the redox system in the cyanobacterial cell, which the cell uses to indirectly sense environmental changes and regulate its circadian rhythm. We aimed to study the effect of certain metabolic and environmental stressors on the PQ pool. We found that in response to phenazine and a phenazine analog, both WT and the circadian rhythm mutants oxidized the PQ pool, but the circadian rhythm mutants were less sensitive. Treatment with red or blue light successfully acted as an additive-free method to skew the redox state of the PQ pool.
Date
7-15-2024
Recommended Citation
Mehra, Himanshu S., "Photosystem II Assembly and Photosynthetic Regulation in Cyanobacteria" (2024). LSU Doctoral Dissertations. 6545.
https://repository.lsu.edu/gradschool_dissertations/6545
Committee Chair
Vinyard, David J.