GSE42035
The acclimation of Chlamydomonas reinhardtii to anaerobiosis involves plant and animal strategies
The absence of oxygen (O2) is a stress condition for aerobic organisms and requires extensive acclimation responses. Previously, Chlamydomonas reinhardtii has been used as a reference organism for understanding these acclimation responses. In this work, we use RNA-Seq for a whole genome view of the acclimation of the organism to dark-anoxic conditions. To distinguish the responses dependent on the COPPER RESPONSE REGULATOR 1 (CRR1), which is also involved in hypoxic gene regulation, we compared the transcriptome of crr1 mutants to that of complemented strains. Nearly 10% of the genome (~ 1,400 genes) are affected by hypoxia based on pairwise comparisons of all strains and two time-points. Comparing transcript profiles from early (hypoxic) with those from late (anoxic) time-points indicated that the cells activated oxidative energy generation pathways before employing fermentative enzymes. Probable substrates included not only carbohydrates but also 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 to N-deprived cells, the TAGs accumulating in hypoxic cells are enriched in desaturated FAs, which distinguishes the contribution of individual pathways for Chlamydomonas TAG accumulation. In crr1 mutants, about 140 genes were aberrantly regulated , re-affirming the importance of CRR1 for the hypoxic response, but indicating also the contribution of additional O2-sensors and signaling strategies to account for the remaining differentially regulated transcripts. We conclude that nitric oxide (NO) dependent signaling cascades, employing both known and novel components, are operative in C. reinhardtii. Overall design: The transcriptome of four different Chlamydomonas strains (wild type CC-124, crr1 mutant, crr1:CRR1 rescued strain and crr1dCys rescued strain) are profiled by RNA-Seq in the dark at different times after the transition from light-oxic to dark-anoxic conditions