The involvement of hydrogen-producing and ATP-dependent NADPH-consuming pathways in setting the redox poise in the chloroplast of Chlamydomonas reinhardtii in anoxia.
; Godaux, Damien ; Cardol, Pierre et al
in The Journal of biological chemistry (2015), 290(13), 8666-76
Photosynthetic microalgae are exposed to changing environmental conditions. In particular, microbes found in ponds or soils often face hypoxia or even anoxia, and this severely impacts their physiology ... [more ▼]
Photosynthetic microalgae are exposed to changing environmental conditions. In particular, microbes found in ponds or soils often face hypoxia or even anoxia, and this severely impacts their physiology. Chlamydomonas reinhardtii is one among such photosynthetic microorganisms recognized for its unusual wealth of fermentative pathways and the extensive remodeling of its metabolism upon the switch to anaerobic conditions. As regards the photosynthetic electron transfer, this remodeling encompasses a strong limitation of the electron flow downstream of photosystem I. Here, we further characterize the origin of this limitation. We show that it stems from the strong reducing pressure that builds up upon the onset of anoxia, and this pressure can be relieved either by the light-induced synthesis of ATP, which promotes the consumption of reducing equivalents, or by the progressive activation of the hydrogenase pathway, which provides an electron transfer pathway alternative to the CO2 fixation cycle. [less ▲]Detailed reference viewed: 126 (2 ULg)
Finding the bottleneck: a research strategy for improved biomass production
; Cardol, Pierre ; et al
in Posten, Clemens; Walter, Christian (Eds.) Microalgal Biotechnology: integration and economy (2012)Detailed reference viewed: 209 (36 ULg)
Impaired respiration discloses the physiological significance of state transitions in Chlamydomonas.
Cardol, Pierre ; ; et al
in Proceedings of the National Academy of Sciences of the United States of America (2009), 106(37), 15979-84
State transitions correspond to a major regulation process for photosynthesis, whereby chlorophyll protein complexes responsible for light harvesting migrate between photosystem II and photosystem I in ... [more ▼]
State transitions correspond to a major regulation process for photosynthesis, whereby chlorophyll protein complexes responsible for light harvesting migrate between photosystem II and photosystem I in response to changes in the redox poise of the intersystem electron carriers. Here we disclose their physiological significance in Chlamydomonas reinhardtii using a genetic approach. Using single and double mutants defective for state transitions and/or mitochondrial respiration, we show that photosynthetic growth, and therefore biomass production, critically depends on state transitions in respiratory-defective conditions. When extra ATP cannot be provided by respiration, enhanced photosystem I turnover elicited by transition to state 2 is required for photosynthetic activity. Concomitant impairment of state transitions and respiration decreases the overall yield of photosynthesis, ultimately leading to reduced fitness. We thus provide experimental evidence that the combined energetic contributions of state transitions and respiration are required for efficient carbon assimilation in this alga. [less ▲]Detailed reference viewed: 41 (11 ULg)