Background:
The lack of sequenced genomes for oleaginous microalgae limits our understanding of themechanisms these organisms utilize to become enriched in triglycerides. Here we report thede novo transcriptome assembly and quantitative gene expression analysis of the oleaginousmicroalga Neochloris oleoabundans, with a focus on the complex interaction of pathwaysassociated with the production of the triacylglycerol (TAG) biofuel precursor.
Results:
After growth under nitrogen replete and nitrogen limiting conditions, we quantified thecellular content of major biomolecules including total lipids, triacylglycerides, starch, protein,and chlorophyll. Transcribed genes were sequenced, the transcriptome was assembled denovo, and the expression of major functional categories, relevant pathways, and importantgenes was quantified through the mapping of reads to the transcriptome. Over 87 million, 77base pair high quality reads were produced on the Illumina HiSeq sequencing platform.Metabolite measurements supported by genes and pathway expression results indicated thatunder the nitrogen-limiting condition, carbon is partitioned toward triglyceride production,which increased fivefold over the nitrogen-replete control. In addition to the observedoverexpression of the fatty acid synthesis pathway, TAG production during nitrogenlimitation was bolstered by repression of the beta-oxidation pathway, up-regulation of genesencoding for the pyruvate dehydrogenase complex which funnels acetyl-CoA to lipidbiosynthesis, activation of the pentose phosphate pathway to supply reducing equivalents toinorganic nitrogen assimilation and fatty acid biosynthesis, and the up-regulation of lipases--presumably to reconstruct cell membranes in order to supply additional fatty acids for TAGbiosynthesis.
Conclusions:
Our quantitative transcriptome study reveals a broad overview of how nitrogen stress resultsin excess TAG production in N. oleoabundans, and provides a variety of genetic engineeringtargets and strategies for focused efforts to improve the production rate and cellular contentof biofuel precursors in oleaginous microalgae.Source:
http://www.biotechnologyforbiofuels.com/rss/