The green algae CO2 concentrating mechanism and photorespiration jointly operate during acclimation to low CO2
- Ousmane Dao
- Marie Bertrand
- Saleh Alseekh
- Florian Veillet
- Pascaline Auroy
- Phuong-Chi Nguyen
- Bertrand Légeret
- Virginie Epting
- Amélie Morin
- Stephan Cuiné
- Caroline L. Monteil
- Luke C. M. Mackinder
- Adrien Burlacot
- Anja Krieger-Liszkay
- Andreas P. M. Weber
- Alisdair R. Fernie
- Gilles Peltier
- Yonghua Li-Beisson
2025-06-17
Due to low availability of CO 2 in aquatic environment, microalgae have evolved a CO 2 concentrating mechanism (CCM). It has long been thought that operation of CCM would suppress photorespiration by increasing the CO 2 concentration at the Rubisco active site, but experimental evidence is scarce. To better explore the function of photorespiration in algae, we first characterized a Chlamydomonas reinhardtii mutant defected in low-CO 2 inducible 20 (LCI20) and show that LCI20 is a chloroplast-envelope glutamate/malate transporter playing a role in photorespiration. By monitoring growth and glycolate excretion in mutants deficient in either CCM or photorespiration, we conclude that: ( i. ) CCM induction does not depend on photorespiration, ( ii. ) glycolate excretion together with glycolate dehydrogenase down-regulation prevents the toxic accumulation of non-metabolized photorespiratory metabolites, and ( iii .) photorespiration is active at low CO 2 when the CCM is operational. This work provides a foundation for a better understanding of the carbon cycle in the ocean where significant glycolate concentrations have been found.