Mechanisms of Light Regulated Translation in Chloroplasts

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This project addresses a fundamental question in biology: How do organisms regulate gene expression to adapt to environmental fluctuations? It focuses on effects of light on the synthesis of proteins required for photosynthesis, a process that consumes atmospheric CO2 and produces the carbohydrates that fuel life. Light drives photosynthesis, but it also damages the photosynthetic apparatus. Repair of the damage requires the replacement of damaged parts with newly synthesized proteins. This project examines how the same light that damages the photosynthetic apparatus also activates the synthesis of new proteins required for repair. An understanding of this repair mechanism has implications for crop productivity and resilience in the face of changing environmental conditions. High school students, high school teachers, and undergraduate students will gain hands-on experience with research through involvement in this project. The primary target of photodamage is a protein called D1, which resides in Photosystem II (PSII) and is encoded by the psbA gene. The rate of D1 synthesis increases with light intensity to provide D1 for PSII repair. In chloroplasts, this regulation occurs at the level of translation. Prior work revealed an intimate connection between light-induced D1 damage, the recruitment of ribosomes specifically to psbA mRNA, and a conserved protein complex in the thylakoid membrane that mediates PSII assembly and repair. This work culminated in a model that invokes the assembly/repair complex as the hub of a translational autoregulatory mechanism that couples psbA translation to the need for D1 following its light-induced damage. Experiments will test and elaborate on this proposed mechanism, with a focus on communication between the membrane-bound assembly complex and a translational activator in the stroma that binds psbA mRNA. Experiments will employ multifaceted genetic, molecular, genomic, and biochemical approaches in maize and Arabidopsis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.