Systemic Cold Stress Adaptation of Chlamydomonas reinhardtii

Abstract

Chlamydomonas reinhardtii is one of the most important model organisms nowadays phylogenetically situated between higher plants and animals (Merchant et al. 2007). Stress adaptation of this unicellular model algae is in the focus because of its relevance to biomass and biofuel production. Here, we have studied cold stress adaptation of C. reinhardtii hitherto not described for this algae whereas intensively studied in higher plants. Toward this goal, high throughput mass spectrometry was employed to integrate proteome, metabolome, physiological and cell-morphological changes during a time-course from 0 to 120 h. These data were complemented with RT-qPCR for target genes involved in central metabolism, signaling, and lipid biosynthesis. Using this approach dynamics in central metabolism were linked to cold-stress dependent sugar and autophagy pathways as well as novel genes in C. reinhardtii such as CKIN1, CKIN2 and a hitherto functionally not annotated protein named CKIN3. Cold stress affected extensively the physiology and the organization of the cell. Gluconeogenesis and starch biosynthesis pathways are activated leading to a pronounced starch and sugar accumulation. Quantitative lipid profiles indicate a sharp decrease in the lipophilic fraction and an increase in polyunsaturated fatty acids suggesting this as a mechanism of maintaining membrane fluidity. The proteome is completely remodeled during cold stress: specific candidates of the ribosome and the spliceosome indicate altered biosynthesis and degradation of proteins important for adaptation to low temperatures. Specific proteasome degradation may be mediated by the observed cold-specific changes in the ubiquitinylation system. Sparse partial least squares regression analysis was applied for protein correlation network analysis using proteins as predictors and Fv/Fm, FW, total lipids, and starch as responses. We applied also Granger causality analysis and revealed correlations between proteins and metabolites otherwise not detectable. Twenty percent of the proteins responsive to cold are uncharacterized proteins. This presents a considerable resource for new discoveries in cold stress biology in alga and plants. Molecular &

Genomic, Transcriptomic, and Proteomic Analysis Provide Insights Into the Cold Adaptation Mechanism of the Obligate Psychrophilic Fungus Mrakia psychrophila

“…AS could enhance proteome diversity; most IR events produce premature termination codon transcripts (Kwon et al 2014), which are turned over by nonsense-mediated decay (NMD) (de Lima Morais and Harrison 2010). Cold-induced AS is also observed in the alga Chlamydomonas reinhardtii (Valledor et al 2013); thus AS might be an important adaptive mechanism for eukaryotic micro-organisms.…”

Real-time iTRAQ-based proteome profiling revealed the central metabolism involved in nitrogen starvation induced lipid accumulation in microalgae

“…Alterations in inoculum size3, growth conditions e.g. light intensity45, temperature67, salinity8, oxidative stress9, UV irradiation2, and nutrient starvation particularly nitrogen61011 induce accumulation of neutral lipid which are further transesterified into biodiesel. However, the biomass is severely impaired.…”

Activation of Autophagy by Metals in Chlamydomonas reinhardtii

“…Deprivation of nutrients (nitrogen, carbon, or sulfur) or progression into stationary growth phase activates autophagy (15)(16)(17)(18)(19). Oxidative stress, photooxidative damage generated by carotenoid deficiency, high light stress, cold stress, or the accumulation of unfolded proteins in the endoplasmic reticulum (ER) also triggers autophagy in Chlamydomonas (19)(20)(21)(22). Moreover, a loss of chloroplast integrity due to depletion of the chloroplastic ClpP protease has been shown to activate autophagy in this alga (23).…”