Light-independent regulation of algal photoprotection by CO2 availability

Description

Photosynthetic algae have evolved mechanisms to cope with suboptimal light and CO2 conditions. When light energy exceeds CO2 fixation capacity, Chlamydomonas reinhardtii activates photoprotection, mediated by LHCSR1/3 and PSBS, and the CO2 Concentrating Mechanism (CCM). How light and CO2 signals converge to regulate these processes remains unclear. Here, we show that excess light activates photoprotection- and CCM-related genes by altering intracellular CO2 concentrations and that depletion of CO2 drives these responses, even in total darkness. High CO2 levels, derived from respiration or impaired photosynthetic fixation, repress LHCSR3/CCM genes while stabilizing the LHCSR1 protein. Finally, we show that the CCM regulator CIA5 also regulates photoprotection, controlling LHCSR3 and PSBS transcript accumulation while inhibiting LHCSR1 protein accumulation. This work has allowed us to dissect the effect of CO2 and light on CCM and photoprotection, demonstrating that light often indirectly affects these processes by impacting intracellular CO2 levels.

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Human Frontiers Science Program RGP0046/2018

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French National Research Agency ANR-18-CE20-0006, ANR-17-EURE-0003, ANR-15-IDEX-02

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Prestige Marie-Curie co-financing grant PRESTIGE-2017-1-0028

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European Union's Horizon 2020 751039

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Carnegie Institution for Science DE-SC0019417

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Marie Curie Initial Training Network Accliphot FP7-PEPOPLE-2012-ITN, 316427

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Japan Society for the Promotion of Science 21H04778, 21H05040

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German Research Foundation HI 739/9.2

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