Date of Award
7-13-2016
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Applied Science
First Advisor
Qingfang He
Abstract
Photosynthetic organisms experience continuous fluctuation in their environment, including changes in light conditions and nutrient availability. These organisms adjust their photosynthetic activity to balance light absorption with the energetic and growth requirements of the cell. This organization provides a mechanism to reduce the formation of potentially damaging reactive oxygen species that result from excessive illumination and excitation of pigment molecules. Cyanobacteria, probable progenitors of chloroplasts, are ancient photosynthetic prokaryotes that have adapted successfully to diverse and adverse environments. Their widespread occurrence and fascinating acclimation capability has rendered them the largest group of photosynthetic prokaryotes on our planet. How these organisms have survived a wide range of adverse environments and what adaptation mechanisms have evolved in cyanobacteria remains to be discovered. Understanding these acclimation strategies will yield results that can be directly applied to higher plants. The aim of the research presented here is to study the physiological and molecular mechanism underlying Synechocystis acclimation under high light and nutrient availability conditions. It emphasizes: (A) The novel high light inducible carotenoid binding protein complex from the thylakoid membrane. This complex was isolated from cells exposed to 24 hours of high light treatment. The protein composition of HLCC was determined to be Slr1128, IsiA, PsaD and HliA/B by mass spectrometry, fluorescence cross-linking, and immuno co-precipitation. The HLCC binds zeaxanthin and myxoxantophyll as major carotenoids and plays a major role in Synechocystis acclimation under excessive illumination. (B) The physiological and biochemical study of Synechocystis 6803 under iron limitation and copper excess. From iron stress cells we have isolated IsiA aggregates bound with carotenoids in thylakoid membrane via sucrose gradient ultra-centrifugation. These IsiA aggregates were characterized by spectroscopy, western blot, and cryo electron microscopy. HPLC results show that the complex binds zeaxanthin, myxoxantophyll, and 3’hydroxyechinenone as major carotenoids. They likely serve to protect PSII from photoxidative stress. Finally, we have investigated copper excess on Synechocystis 6803 lacking Slr1573 gene that codes for the laccase protein. We report a toxic dose of 3µM CuCl2 and a non-inhibitory dose of 1.5µM under normal light condition. This toxicity of copper is aggravated under high light conditions, demonstrated by a dramatic reduction in chlorophyll content and photosynthetic activity accompanied by a depletion of trimeric photosystem I making PSII more vulnerable to photo oxidation. Finally, pigment analysis by HPLC shows that the Slr1573 deletion strain is involved in carotenoid biosynthesis, especially in treated cells under high light, thus providing a support and quenching mechanism for dissipation of excess energy due to high light and copper toxicity compared to wild type. Overall, this study yields important insight into the molecular and physiological mechanism in Synechocystis acclimation strategies. The identification and characterization of the HLCC not only will be of great interest to scientists working on photosynthesis and protein biochemistry, but also will be appealing to a general audience, related to synthetic biology and renewable energy production.
Recommended Citation
Daddy Gaoh, Soumana, "Analysis of the Stress - Inducible Carotenoid - Binding Protein Complex from Synechocystis PCC 6803" (2016). Theses and Dissertations. 684.
https://research.ualr.edu/etd/684
