Carbon Supply and Photoacclimation Cross Talk in the Green Alga Chlamydomonas reinhardtii

Abstract

Photosynthetic organisms are exposed to drastic changes in light conditions, which can affect their photosynthetic efficiency and induce photodamage. To face these changes, they have developed a series of acclimation mechanisms. In this work, we have studied the acclimation strategies of Chlamydomonas reinhardtii, a model green alga that can grow using various carbon sources and is thus an excellent system in which to study photosynthesis. Like other photosynthetic algae, it has evolved inducible mechanisms to adapt to conditions where carbon supply is limiting. We have analyzed how the carbon availability influences the composition and organization of the photosynthetic apparatus and the capacity of the cells to acclimate to different light conditions. Using electron microscopy, biochemical, and fluorescence measurements, we show that differences in CO 2 availability not only have a strong effect on the induction of the carbon-concentrating mechanisms but also change the acclimation strategy of the cells to light. For example, while cells in limiting CO 2 maintain a large antenna even in high light and switch on energy-dissipative mechanisms, cells in high CO 2 reduce the amount of pigments per cell and the antenna size. Our results show the high plasticity of the photosynthetic apparatus of C. reinhardtii. This alga is able to use various photoacclimation strategies, and the choice of which to activate strongly depends on the carbon availability.

Chlamydomonas reinhardtii responding to high light: a role for 2‐propenal (acrolein)

“…Exposing cells to 4 h HL led to a similarly large increase in the de‐epoxidation state of VAZ pool under either growth condition. These data confirm the large difference in the de‐epoxidation state between mixotrophically and photoautotrophically grown C. reinhardtii previously reported (Polukhina et al ). As has been stated by these authors, C. reinhardtii shows a high plasticity of the photosynthetic apparatus in response to growth conditions.…”

Ubiquitin ligase component LRS1 and transcription factor CrHy5 act as a light switch for photoprotection inChlamydomonas

“…In the green microalga C. reinhardtii , efficient energy-dependent quenching requires the proteins LHCSR3 (Peers et al, 2009) and LHCSR1 (Dinc et al, 2016) besides PSBS (Correa-Galvis et al, 2016; Tibiletti et al, 2016), whose accumulation is induced by light stress (Peers et al, 2009; Maruyama et al, 2014). In addition to light, the supply of inorganic and organic carbon regulates the accumulation of LHCSR proteins, with LHCSR3 light induction being repressed by high inorganic/organic carbon supply, whereas LHCSR1 accumulation is unaffected (Polukhina et al, 2016). Similar to LHCSR3, PSBS accumulation is repressed when cells are exposed to high concentrations of carbon dioxide (Correa-Galvis et al, 2016).…”

The mitochondrial alternative oxidase from Chlamydomonas reinhardtii enables survival in high light

“…Interestingly, upon exposure of C. reinhardtii to HL, metabolites associated with both the CBBC and TCA cycle increased, suggesting rapid movement of metabolites from chloroplasts to mitochondria. Rapid exchange of metabolites between mitochondria and chloroplasts may be facilitated through direct physical associations between the organelles; it was noted that mitochondria are centrally positioned in C. reinhardtii cells under mixotrophic, low-light conditions, whereas upon exposure to high light, they move to the cell's periphery, becoming wedged between the plasma membrane and chloroplast, where they appear appressed to the chloroplast envelope (94).…”