Light is required for photosynthesis, which is the ultimate source of energy in food for almost all living things on earth. However, when the light energy absorbed by photosynthetic cells exceeds the photosynthetic capacities, reactive oxygen species are generated in the cells, causing oxidative damage to proteins, lipids, and photosynthetic pigments. These detrimental effects are amplified by other environmental stresses (e.g. low temperature, drought). Under suboptimal growth conditions plants or algae cannot efficiently use the reducing power generated by photosynthesis. This lowers the light intensity at which excess light absorption leads to photo-damage. Hence, photosynthetic organisms unavoidably face light stress as well during all other stress conditions. However, in spite of the importance of light stress in relation to crop productivity, the molecular mechanisms of light-stress responses have not yet been elucidated in plants or photosynthetic microbes. The goal of this project is to determine the molecular mechanisms by which photosynthetic organisms protect themselves from high intensity light. The research focuses on analysis of the functions of a family of four high light-inducible proteins (HLIP) in the model organism Synechocystis PCC 6803. HLIPs resemble the light-harvesting chlorophyll a/b-binding proteins of higher plants in their primary sequences. They have been proven to be essential for cyanobacteria to survive exposure to high light. It may also play a critical role in higher plants as well. To investigate the functions of HLIPs and associated-proteins in cell survival during exposure to high light, the regulator PfsR (photosynthesis, Fe homeostasis and stress-response regulator) will be further characterized in order to understand its roles in protection against high intensity light. The second-site mutation in at least one of the five suppressors that restore viability in high light to the quadruple hli deletion mutant will be pinpointed. These studies will reveal the mechanisms of cell survival and the functions of HLIPs in high light. In addition, the effects of HLIP and photosystem I trimer interaction and the role of the pigment-binding motifs in HLIPs will be defined by site-directed mutagenesis. Furthermore, a novel high light-inducible, carotenoid-binding protein complex in the thylakoid membrane will be characterized. Overall, the research will improve understanding of the mechanisms for survival of photosynthetic organisms under high light conditions and will eventually enhance the ability to develop rational strategies for engineering plants or algae for better stress tolerance.
Broader Impact The research subject is of general interest to plant biologists. The research allows students and postdoctoral fellows to integrate approaches of genetics, biochemistry and biophysics in their educational and research programs, fostering highly competitive and novel research initiatives important to agriculture and biofuel production. It will prepare the trainees for independent research careers. In addition, it will improve the strength of photosynthesis research in Arkansas. The project will allow the PI to continue involving underrepresented minority students in research, contributing to their retention in higher education. About 35% UALR undergraduates (more than 4000 students) are from underrepresented groups, but few have opportunities for research training due to the shortage of laboratory space and active faculty research programs. Furthermore, this project will stimulate additional funding for the training of undergraduate students through State- or UALR-sponsored programs that involve minority students.