Abstract
BackgroundChromochloris zofingiensis, an oleaginous microalga, is a promising feedstock for the co-production of triacylglycerol (TAG)-based biodiesel and the high-value product astaxanthin. To reveal the molecular mechanism of TAG and astaxanthin biosynthesis during transitions of sulfur nutritional status, namely sulfur-starvation (SS) and sulfur-replenishment (SR), the physiological responses and the transcriptomic dynamics of C. zofingiensis were examined.ResultsThe results revealed a reversible TAG and astaxanthin accumulation under SS, which is correlated with the reduction of cell growth and protein content, indicating the reallocation of carbon. By correlating the data on the physiological and transcriptional responses to different sulfur nutritional status, a model for the underlying mechanism of TAG and astaxanthin accumulation in C. zofingiensis was postulated, which involved up-regulation of key genes including diacylglycerol acyltransferase (DGTT5) and beta-carotene ketolase (BKT1), increased energy and NADPH supply by elevating the tricarboxylic acid (TCA) cycle and the oxidative pentose phosphate (OPP) pathway, and the increased carbon precursors (pyruvate and acetyl-CoA) through central carbon metabolism. In addition, the net enhancement of the de novo biosynthesis of fatty acids and the re-direction of the terpenoid precursors toward the branch catalyzed by lycopene beta cyclase (LCYb) and BKT1 escalated the substrate availability for the biosynthesis of TAG and astaxanthin, respectively.ConclusionsIn this study, the time-resolved transcriptional analysis of C. zofingiensis under SS and SR conditions was reported for the first time to elucidate the regulatory roles of key enzymes, including DGTT5, BKT1 and LCYb, in the underlying mechanisms of TAG and astaxanthin accumulation.
Highlights
Chromochloris zofingiensis, an oleaginous microalga, is a promising feedstock for the co-production of triacylglycerol (TAG)-based biodiesel and the high-value product astaxanthin
Knowledge on the metabolism of lipids and astaxanthin in C. zofingiensis is still sparse; especially the mechanisms and factors involved in the transcriptional regulation is largely unclear, despite key genes associated with the TAG and astaxanthin biosynthesis pathways having been identified via bioinformatic analysis [9,10,11]
Sulfur‐starvation leads to cell growth inhibition and cellular Reactive oxygen species (ROS) accumulation A two-phase cultivation was conducted to assess the effects of SS and SR (Fig. 1a)
Summary
Chromochloris zofingiensis, an oleaginous microalga, is a promising feedstock for the co-production of triacylglycerol (TAG)-based biodiesel and the high-value product astaxanthin. Chromochloris zofingiensis is able to accumulate TAG and astaxanthin under stress conditions, such as nutrient depletion and high light [7, 8]. Knowledge on the metabolism of lipids and astaxanthin in C. zofingiensis is still sparse; especially the mechanisms and factors involved in the transcriptional regulation is largely unclear, despite key genes associated with the TAG and astaxanthin biosynthesis pathways having been identified via bioinformatic analysis [9,10,11]. It is important to determine the parameters on the stress-induced accumulation of TAG and astaxanthin in C. zofingiensis and study the underlying metabolic mechanisms, the knowledge from which would aid further development of the co-production of microalgal biodiesel and high-value products
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