Photoinhibition: Nature of the process and Influence on primary productivity Across Scales

Photosynthetic microbes contribute over 50% of carbon fixation on Earth.

Inhabiting extremely diverse environments, they always have to cope with a friend that is simultaneously their enemy: sunlight.

Photon energy is necessary for photosynthesis, but it continuously damages the photosynthetic apparatus, primarily the first enzyme in oxygenic photosynthesis Photosystem II (PSII) in the process of photoinhibition.

Upon photodamage, PSII becomes irreversibly inactivated, unable to do electron transfer, and requires costly repair involving protein translation. Photoinhibition represents a major limiting factor to terrestrial and aquatic photosynthesis.

Despite decades of research on PSII and photoinhibition, many key aspects of photoinhibition remain unresolved, among them: -the site within the PSII complex where the photoinhibitory damage takes place, as well as its molecular nature -partitioning of the known different types of damage, dependent on the environment and conditions -the role of the mysterious haem b559, conserved in phototrophs close to PSII reaction centre and transferring electrons, long speculated to play a role in photoprotection but with no convincing role assigned to date In PHOTONICS, I aim to focus on these issues to provide a thorough description of photoinhibition and photoprotection strategies in photosynthetic microbes.

I will use a combination of novel in vivo methods, taking advantage of the most recent developments in time-resolved fluorescence- and absorption spectroscopies. These will be combined with genetics and state-of-the-art structural biology.

It is the integrative nature of PHOTONICS, bridging different scales of complexity in a hypothesis-driven manner, that will allow to finally resolve the critical missing pieces of PSII function and damage.

Finally, it will provide a methodological blueprint for assessment of photoinhibition in situ, and aid modelling of photosynthetic productivity under fluctuating conditions.