Systems Analysis of the Response of Photosynthesis, Metabolism, and Growth to an Increase in Irradiance in the Photosynthetic Model OrganismChlamydomonas reinhardtii     

Abstract

We investigated the systems response of metabolism and growth after an increase in irradiance in the nonsaturating range in the algal model Chlamydomonas reinhardtii. In a three-step process, photosynthesis and the levels of metabolites increased immediately, growth increased after 10 to 15 min, and transcript and protein abundance responded by 40 and 120 to 240 min, respectively. In the first phase, starch and metabolites provided a transient buffer for carbon until growth increased. This uncouples photosynthesis from growth in a fluctuating light environment. In the first and second phases, rising metabolite levels and increased polysome loading drove an increase in fluxes. Most Calvin-Benson cycle (CBC) enzymes were substrate-limited in vivo, and strikingly, many were present at higher concentrations than their substrates, explaining how rising metabolite levels stimulate CBC flux. Rubisco, fructose-1,6-biosphosphatase, and seduheptulose-1,7-bisphosphatase were close to substrate saturation in vivo, and flux was increased by posttranslational activation. In the third phase, changes in abundance of particular proteins, including increases in plastidial ATP synthase and some CBC enzymes, relieved potential bottlenecks and readjusted protein allocation between different processes. Despite reasonable overall agreement between changes in transcript and protein abundance (R 2 = 0.24), many proteins, including those in photosynthesis, changed independently of transcript abundance.

ACHT4-driven oxidation of APS1 attenuates starch synthesis under low light intensity in Arabidopsis plants

“…3B), suggesting that AGPase redox regulation might also play a role in stimulating a transient burst of starch synthesis to accommodate an abruptly increased light intensity, as suggested in ref. 23. The concomitant gradual decrease of both APS1-ACHT4 RIs levels and reduced APS1 upon lowering the light intensity and the abrupt increase in both upon increased intensity further supported the notion that ACHT4 reacted with the reduced APS1.…”

“…3B) and consequently starch synthesis in response to small and abrupt fluctuations in light intensity during the day. In a recent study assessing photosynthesis, metabolism, and growth responses to an increase in irradiance in the unicellular green alga C. reinhardtii, a rapid increase in starch levels was suggested to uncouple photosynthesis from growth in a fluctuating light environment, by providing a transient buffer for carbon until growth increased (23). The rapid response of the APS1 redox state in Arabidopsis plants exposed to fluctuating light intensity (Fig.…”

“…Such activity might be important for the rationing of photosynthates to starch and sugars exported from the chloroplast during the day. Alternatively, as shown in the unicellular green alga Chlamydomonas reinhardtii, such activity may regulate the levels of starch to be used as a transient pool for reduced carbon in a fluctuating light environment (23). We tested this hypothesis by subjecting the plants to small fluctuations of light intensity during the day.…”

Systems-Wide Analysis of Acclimation Responses to Long-Term Heat Stress and Recovery in the Photosynthetic Model OrganismChlamydomonas reinhardtii

“…Sample derivatization and GC-MS analysis of polar metabolites was done as described previously Mettler et al, 2014), except that during derivatization only 20 and 40 mL of volume for the methoxamination and sylilation steps were used, respectively. The ChromaTOF software (version 3.22; LECO) was used to visually inspect, baseline correct, and export the GC-MS raw data into NetCDF file format with the following settings: baseline offset, 1.0; smoothing of data points, 5; signal-to-noise ratio, 10.…”

“…In fact, Chlamydomonas is an ideal plant model for such approaches because (1) as a single-celled organism all cells are of the same type and different cell cycle stages may be averaged out by growing cells in asynchronous cultures, (2) cells can be cultured under highly controlled conditions and changes in environmental conditions applied homogenously, (3) gene families are less complex than those of land plants (Merchant et al, 2007). Accordingly, several recent studies have taken advantage of these characteristics to deepen our understanding of acclimation responses to N starvation (Blaby et al, 2013;Schmollinger et al, 2014), copper and iron limitation (Castruita et al, 2011;Höhner et al, 2013), anoxia (Hemschemeier et al, 2013), or increasing light (Mettler et al, 2014).…”