PT  - JOURNAL ARTICLE
AU  - Adrien Burlacot
AU  - Ousmane Dao
AU  - Pascaline Auroy
AU  - Stephan Cuiné
AU  - Yonghua Li-Beisson
AU  - Gilles Peltier
TI  - Alternative electron pathways of photosynthesis drive the algal CO<sub>2</sub> concentrating mechanism
AID  - 10.1101/2021.02.25.432959
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.02.25.432959
4099  - http://biorxiv.org/content/early/2021/02/27/2021.02.25.432959.short
4100  - http://biorxiv.org/content/early/2021/02/27/2021.02.25.432959.full
AB  - Global photosynthesis consumes ten times more CO2 than net anthropogenic emissions, and microalgae account for nearly half of this consumption1. The great efficiency of algal photosynthesis relies on a mechanism concentrating CO2 (CCM) at the catalytic site of the carboxylating enzyme RuBisCO, thus enhancing CO2 fixation2. While many cellular components involved in the transport and sequestration of inorganic carbon (Ci) have been uncovered3,4, the way microalgae supply energy to concentrate CO2 against a thermodynamic gradient remains elusive4-6. Here, by monitoring dissolved CO2 consumption, unidirectional O2 exchange and the chlorophyll fluorescence parameter NPQ in the green alga Chlamydomonas, we show that the complementary effects of cyclic electron flow and O2 photoreduction, respectively mediated by PGRL1 and flavodiiron proteins, generate the proton motive force (pmf) required by Ci transport across thylakoid membranes. We demonstrate that the trans-thylakoid pmf is used by bestrophin-like Ci transporters and further establish that a chloroplast-to-mitochondria electron flow contributes to energize non-thylakoid Ci transporters, most likely by supplying ATP. We propose an integrated view of the CCM energy supply network, describing how algal cells distribute photosynthesis energy to power different Ci transporters, thus paving the way to the transfer of a functional algal CCM in plants towards improving crop productivity.One sentence summary Photosynthetic alternative electron flows and mitochondrial respiration drive the algal CO2 concentrating mechanismCompeting Interest StatementThe authors have declared no competing interest.BSTBestrophin-like proteinsCCMCarbon Concentrating MechanismCEFCyclic Electron FlowCiInorganic CarbonCMEFChloroplast-Mitochondria Electron FlowHLA3High Light Activated 3LCILow Carbon InducedLEFLinear Electron FlowLHCSR3Light Harvesting Complex Stress Related 3MyxoMyxothiazolNPQNon Photochemical QuenchingPCEFPseudo-Cyclic Electron FlowPGRL1Proton Gradient Regulation Like-1FLVsFlavodiiron proteinsPSIPhotosystem IPSIIPhotosystem IIRuBisCORibulose Bisphosphate Carboxylase OxygenaseSHAMSalicyl hydroxamic acid.