Time-dependent transcriptome profile of genes involved in triacylglycerol (TAG) and polyunsaturated fatty acid synthesis in Nannochloropsis gaditana during nitrogen starvation

Jorijn H Janssen,Jasper J Koehorst,René H Wijffels,Peter J Schaap,Jacco Spoelder,Maria J Barbosa

doi:10.1007/s10811-019-02021-2

Jorijn H Janssen, Jasper J Koehorst + Show 4 more

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https://doi.org/10.1007/s10811-019-02021-2

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Abstract

In this research, the gene expression of genes involved in lipid metabolism of the eustigmatophyte alga Nannochloropsis gaditana was measured by transcriptomic data. This microalga can be used as a source of triacylglycerol (TAG) and the omega-3 fatty acid eicosapentaenoic acid (EPA). Insight in TAG and EPA production and regulation are needed to improve their productivity. Nitrogen starvation induces TAG accumulation in N. gaditana. Previous research showed that during nitrogen starvation, EPA was translocated from the polar lipids to TAG and de novo synthesized in N. gaditana. Therefore, the expression levels of genes involved in fatty acid translocation and de novo TAG synthesis were measured. Furthermore, the genes involved in de novo EPA synthesis such as elongases and desaturases were studied. The expression levels were measured during the first hours of nitrogen starvation and the subsequent period of 14 days. One phospholipid:diacylglycerol acyltransferase (PDAT) gene involved in translocation of fatty acids from membrane lipids to TAG was upregulated. In addition, several lipases were upregulated, suggesting that these enzymes might be responsible for the translocation of EPA to TAG. Most desaturases and elongases involved in de novo EPA synthesis were downregulated during nitrogen starvation, except for Δ9 desaturase which was upregulated. This upregulation correlates with the increase in oleic acid. Due to the presence of many hypothetical genes, improvement in annotation is needed to increase our understanding of these pathways and their regulation.

Highlights

Microalgae are a sustainable source of lipids which can be used for food, feed and fuel
Transcriptional expression levels of genes involved in TAG and eicosapentaenoic acid (EPA) synthesis showed a complex regulation
Multiple copies of the genes were identified and might indicate different localization in the cell. Some of these gene copies involved in the acyl-CoA dependent pathway for de novo TAG synthesis were upregulated (e.g. glycerol-3-phosphate acyltransferase (GPAT) and diacylglycerol acyltransferase (DGAT))

Summary

Introduction

Microalgae are a sustainable source of lipids which can be used for food, feed and fuel. Fatty acids can accumulate in triacylglycerol (TAG) lipid droplets and in membrane lipids. Nannochloropsis gaditana is a microalga known for its large. TAG accumulation during nitrogen starvation and the production of omega-3 fatty acid eicosapentaenoic acid (EPA) during growth. The genome of N. gaditana has been sequenced (Radakovits et al 2012; Corteggiani Carpinelli et al 2014; Schwartz et al 2018), which enables transcriptomic analysis by measuring the expression levels using RNA sequencing (RNA-seq). The expression levels give information about the transcriptional activity of the genes in the studied pathways

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