Elucidating the influence of dynamic FNR interactions on photosynthetic electron transfer and photosystem I photoprotection

Context. Plants, algae and bacteria convert light into chemical energy to power the fixation of carbon dioxide into biomass, providing the oxygen and food that sustains the biosphere. However, natural photosynthesis operates with an efficiency of only ~2-3% in most species and even these modest figures are now threatened by the severe weather associated with climate change. Against this backdrop there is increased demand for food and biofuel production to meet the needs of a growing population. Recent work has shown that genetic interventions aimed at improving photosynthetic photoprotection can increase tolerance to environmental stress and boost yield. However, the success of future interventions requires the fundamental underpinning science. A key area requiring improved understanding is the photoprotection of photosystem I, the most abundant solar-powered machine on Earth. The challenge. The chlorophyll-proteins photosystems I and II (PSI and PSII), within the chloroplast of plants and algae, convert light into chemical energy to power CO2 fixation into biomass. PSI and PSII are exceptional at harvesting solar energy, even when light is scarce. However, the flipside of this success is that on sunny days PSI and PSII are extremely susceptible to light-induced damage. PSII has evolved a complex, but very effective repair cycle to mitigate these sunburn symptoms. PSI on the other hand has no such repair cycle and therefore plants and algae go to great lengths to protect it from damage. Our recent work using gene editing in model green algae provided evidence that the location of a photosynthetic electron transfer protein, known as FNR, is critical to controlling photoprotection of PSI. This insight was obtained by artificially linking the FNR protein to either PSI or cytochrome b6f, the protein complex that mediates electron transfer between PSII and PSI. The challenge now is to understand why and establish the mechanistic basis of PSI photoprotection. Aims and objectives. Compare the mutant and wild-type algae to determine how different locations of FNR on the membrane affect electron transfer and photoprotection functions. Elucidate the proteins FNR interacts with under conditions favouring photosynthesis or photoprotection. Understand how the structure and function of PSI and cytochrome b6f are affected through their interaction with FNR. Potential applications and benefits. PSI photoprotection is crucial to the fitness and growth of plants and algae. If we can understand how this elusive process is regulated, we can make a significant contribution to improving their hardiness to climate change, which threatens to imperil our food supply. Furthermore, this work may provide a new platform for enhancing biofuel (e.g. hydrogen) production in algae to support our transition towards net zero CO2. Relevance to BBSRC strategy. It provides a further stride to understanding photosynthesis at the molecular level, revealing bottlenecks in the electron transfer systems. These findings may provide future genetic targets to improve productivity in food crops and light-powered cell factories, used for biofuel, pharmaceutical and high-value commodity chemical synthesis, thus addressing ‘sustainable agriculture and food’ and ‘renewable resources and clean growth’ priorities. The development of the TurboID and redox proteomic techniques to quantify protein-protein associations and downstream signalling will be applicable to a wide range of protein complexes involved in diverse cellular processes, thus addressing the ‘Transformative technologies’ priority. Finally, uncovering how structure and function are linked to power cellular bioenergetics, addresses the ‘Understanding the rules of life’ priority.