Humankind must increase photosynthetic capacity to enhance CO2 fixation for food and fuel production and the mitigation of climate change. Growth of photosynthetic organisms is directly affected by suboptimal environmental conditions, which lowers photosynthetic efficiency by stimulating the production of reactive oxygen species, which are causing damage to cellular processes. Photoprotection and repair are key for the maintenance of the photosynthetic apparatus, preventing damage and maintaining high photosynthetic yields. Understanding photoprotective mechanisms is essential to develop new strategies for the optimization of photosynthesis to meet the global need for food and energy. Photosynthetic organisms are exposed to varying light qualities and quantities throughout the day. When photosynthetic cells absorb an excess of light, they activate non-photochemical quenching – a mechanism to dissipate excess absorbed light energy as heat which depends on specific “high light inducible“ proteins within light harvesting complexes in algae and plants.
We investigated the effect of light intensity, light quality, photosynthetic electron transport, and carbon dioxide on the activation of 3 photoprotective genes (LHCSR1, LHCSR3, and PSBS) during dark-to-light transition using the green alga Chlamydomonas reinhardtii. We found strong induction at very low light intensities, which was modulated independently by blue and UV-B radiation via specific photoreceptors; only LHCSR3 was strongly controlled by carbon dioxide levels via a putative enhancer function of CIA5, a transcription factor that controls genes of the carbon concentrating mechanism. We present a model that incorporates separate signaling pathway inputs and proposes how cells anticipate diel fluctuations to survive in a changing light environment.Host: PD Dr. Marion Eisenhut