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

Introduction

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.

Photodamage and Repair

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.

Unresolved Aspects of Photoinhibition

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 the PSII reaction centre and transferring electrons, long speculated to play a role in photoprotection but with no convincing role assigned to date.

Project Goals

In PHOTONICS, I aim to focus on these issues to provide a thorough description of photoinhibition and photoprotection strategies in photosynthetic microbes.

Methodology

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.

Integrative Approach

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

Expected Outcomes

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