How cells adapt to fluctuating energy inputs: insights from the green microalgae Chlamydomonas.

On Earth, oxygenic photosynthesis is the main process responsible for carbon input into ecosystems, transforming annually more than 100GT of CO₂ into biomass. During photosynthesis, sunlight is converted by the photosynthetic electron transport chain into ATP and NADPH which are used by the metabolism to transform CO₂ into biomass. However, in their natural habitat, sunlight energy is provided at fluctuating intensities with variable timescales. Such fluctuations can cause a mismatch between metabolic energy demand and energy production, causing over-reduction of the photosynthetic electron transport chain and the generation of reactive oxygen species can cause photooxidative damage, and lead to cell death. Here, we developed a method to quantify in high throughput the ability of microalgal strains to sustain photosynthesis under various light fluctuation patterns in the microalga Chlamydomonas reinhardtii. By using this new tool on a Chlamydomonas mutant library consisting of single knock-out mutants representing 18% of the genome, we propose a new systems view of how photosynthetic organisms maintain energetic homeostasis under fluctuating light environments. By further exploring the role of key mechanisms involved in protein repair, membrane composition or redox transport, we further unravel new principles on how the cellular bioenergetic status of the cell is dynamically maintained. We will discuss how unravelling the bioenergetic landscape of cells can lead to biotechnological improvement of CO₂ capture and biomass production for the building of a resilient bioeconomy.