Transcriptome and Gene Expression Analysis of an Oleaginous Diatom Under Different Salinity Conditions

Diatoms constitute a remarkably diverse and attractive group of microalgae, serving as the main primary producers in many ecosystems and a potential source of renewable biofuel. The enhancement of lipid production in diatoms has been achieved by the optimization of culture conditions, such as temperature, salinity, and nutrient starvation. In this study, we performed Illumina sequencing and the de novo transcriptome assembly of an oleaginous diatom, Nitzschia sp., which produces up to 50 % oil by weight under defined conditions. High-quality reads were assembled into 28,117 isogenes and then subjected to BLAST alignment, Gene Ontology annotation, and KEGG Orthology annotation. The majority of genes and pathways related to cell wall formation and lipid biosynthesis were identified by these analyses. In addition, elevated salinity was found to increase the total lipid content of Nitzschia sp. For a better understanding of the molecular mechanisms regulating this phenomenon, transcriptome profiles under different conditions of salinity were compared to examine how the metabolic flux was channeled to increase the biosynthesis of triacylglycerols. As expected, a subset of genes involved in lipid biosynthesis was up-regulated under salinity stress. Meanwhile, carbon and nitrogen metabolism genes were also significantly affected, indicating a diversion of metabolic pathways. The data we generated here enrich the genomic resources available for non-model algae and provide insights into the mechanisms of lipid accumulation in microalgae.