COPPER RESPONSE REGULATOR1–Dependent and –Independent Responses of theChlamydomonas reinhardtiiTranscriptome to Dark Anoxia

Abstract

Anaerobiosis is a stress condition for aerobic organisms and requires extensive acclimation responses. We used RNA-Seq for a whole-genome view of the acclimation of Chlamydomonas reinhardtii to anoxic conditions imposed simultaneously with transfer to the dark. Nearly 1.4 3 10 3 genes were affected by hypoxia. Comparing transcript profiles from early (hypoxic) with those from late (anoxic) time points indicated that cells activate oxidative energy generation pathways before employing fermentation. Probable substrates include amino acids and fatty acids (FAs). Lipid profiling of the C. reinhardtii cells revealed that they degraded FAs but also accumulated triacylglycerols (TAGs). In contrast with N-deprived cells, the TAGs in hypoxic cells were enriched in desaturated FAs, suggesting a distinct pathway for TAG accumulation. To distinguish transcriptional responses dependent on COPPER RESPONSE REGULATOR1 (CRR1), which is also involved in hypoxic gene regulation, we compared the transcriptomes of crr1 mutants and complemented strains. In crr1 mutants, ;40 genes were aberrantly regulated, reaffirming the importance of CRR1 for the hypoxic response, but indicating also the contribution of additional signaling strategies to account for the remaining differentially regulated transcripts. Based on transcript patterns and previous results, we conclude that nitric oxide-dependent signaling cascades operate in anoxic C. reinhardtii cells.

Methylcrotonyl-CoA Carboxylase Regulates Triacylglycerol Accumulation in the Model Diatom Phaeodactylum tricornutum

“…On the other hand, expression of MCC2 in Arabidopsis thaliana was not induced by nitrate nor Fe starvation and neither by varying ammonium or CO 2 concentrations (https://www.genevestigator.com/gv/plant.jsp). In C. reinhardtii, MCC1 (ProtID_193008) and MCC2 (ProtID_303940) were either downregulated or showed no significant changes under N-deprived conditions (Miller et al, 2010), although they are activated in anoxic conditions (Hemschemeier et al, 2013). The regulation of MCC in diatoms therefore appears to be fundamentally different from that in plants and green algae.…”

Nitric Oxide–Triggered Remodeling of Chloroplast Bioenergetics and Thylakoid Proteins upon Nitrogen Starvation inChlamydomonas reinhardtii

“…Yet, the phenotype of nit2 cells shows that the NaR catalytic activity per se is not required for productive NO synthesis during nitrogen starvation, as was also observed in anoxic conditions (Hemschemeier et al, 2013a(Hemschemeier et al, , 2013b. NaR activity appears also dispensable for nitrite-dependent NO synthesis in Scenedesmus (Mallick et al, 1999) but seems required for NO evolution from nitrite by C. reinhardtii cells grown in nitrogenreplete conditions (Sakihama et al, 2002).…”

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

“…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).…”