Photoprotection is regulated by light-independent CO 2 availability
2021
Petroutsos, Dimitris | Ruiz-Sola, M. Águila | Flori, Serena | Yuan, Yizhong | Villain, Gaelle | Sanz-Luque, Emanuel | Redekop, Petra | Tokutsu, Ryutaro | Kueken, Anika | Tsichla, Angeliki | Kepesidis, Georgios | Allorent, Guillaume | Arend, Marius | Iacono, Fabrizio | Finazzi, Giovanni | Hippler, Michael | Nikoloski, Zoran | Minagawa, Jun | Grossman, Arthur
Abstract Photosynthetic algae cope with suboptimal levels of light and CO 2 . In low CO 2 and excess light, the green alga Chlamydomonas reinhardtii activates a CO 2 Concentrating Mechanism (CCM) and photoprotection; the latter is mediated by LHCSR1/3 and PSBS. How light and CO 2 signals converge to regulate photoprotective responses remains unclear. Here we show that excess light activates expression of photoprotection- and CCM-related genes and that depletion of CO 2 drives these responses, even in total darkness. High CO 2 levels, derived from respiration or impaired photosynthetic fixation, repress LHCSR3 and CCM genes while stabilizing the LHCSR1 protein. We also show that CIA5, which controls CCM genes, is a major regulator of photoprotection, elevating LHCSR3 and PSBS transcript accumulation while inhibiting LHCSR1 accumulation. Our work emphasizes the importance of CO 2 in regulating photoprotection and the CCM, demonstrating that the impact of light on photoprotection is often indirect and reflects intracellular CO 2 levels.
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