Oxygenic photosynthesis at its energy limit: Membranes and proteins for growth in the near infrared

• Applicant: Dennis Nürnberg, Ph.D.
• Subject Area: Plant Biochemistry and Biophysics
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429536723

Oxygenic photosynthesis uses chlorophyll a to convert solar energy into the chemical energy that powers the biosphere. Chlorophyll a absorbs sun light only up to 700 nm, the so-called "red limit", which coincides with the classical energy threshold of the primary photosynthetic reactions. Some cyanobacteria are able to extend this limit by using modified chlorophylls. There is great interest in understanding how long-wavelength/lower-energy light can drive photosynthesis as this could provide the basis for the design of bioengineered or artificial photosynthesis with increased solar-energy conversion efficiency. Chlorophyll f is the most red-shifted chlorophyll in oxygenic photosynthesis. It allows the cyanobacteria to grow in near-infrared light and provides advantages to life in deeply shaded environments that cannot be occupied by other phototrophs. Chlorophyll f is not only involved in light harvesting but also replaces key pigments in the heart of the reaction centre in photosystem I (PSI) and photosystem II (PSII), where it actually performs the far-red photochemistry.This project aims to understand how the membranes and photosynthetic proteins change during far-red light (FRL) photoacclimation to allow the system to function efficiently using the lower energy photons of near infra-red light. Previous work by the applicant and his collaborators has led to a model in which the long-wavelength chlorophylls are the primary electron donors in both photosystems. An extended set of spectroscopic, biochemical and molecular biological methods will be used in this work to strengthen the developed model and understand the basics of this new type of photosynthesis. The long-wavelength chlorophylls in PSI and PSII shall be located by using a newly built low-temperature absorption spectrophotometer, in combination with crystallographic data; their functional role shall be determined by fluorescence, absorption, FTIR and EPR spectroscopy. The results obtained from the native chlorophyll f-systems shall be then used to modify chlorophyll a-cyanobacteria and test them for the ability to shift their photosynthetic activity into the far-red. The applicant hypothesized that there are certain trade-offs for the FRL-system, such as a higher susceptibility to photodamage when exposed to varying light conditions. These structure-function predictions shall be tested on cell and protein level. Besides the changes in protein structure and associated changes in electron transport, the influence of FRL on membrane structure and organisation will be addressed by super-resolution microscopy and AFM, with a focus on the formation of specialised membrane domains.The overall findings from this project will provide important new insights into the mechanism of light acclimation and the energetic limits of oxygenic photosynthesis. In addition, they will be of relevance for engineering near-infrared plants with potentially higher photosynthetic efficiency.

• DFG Programme: Independent Junior Research Groups
• Major Instrumentation: Low-temperature transient absorption spectroscopy setup
• Instrumentation Group: 5700 Festkörper-Laser