Characterization of Fatty Acid EXporters involved in fatty acid transport for oil accumulation in the green alga Chlamydomonas reinhardtii

Nannan Li,Shengting Li,Shufeng Wang,Yasuo Igarashi,Feng Luo,Yan Zhang,Hongjun Meng,Zhongchun Xiao,Qing Li,Peng Chang,Liang Guo,Xiaohui Zhang

doi:10.1186/s13068-018-1332-4

Nannan Li, Shengting Li + Show 10 more

Open Access

https://doi.org/10.1186/s13068-018-1332-4

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Abstract

BackgroundIn the past few decades, microalgae biofuel has become one of the most interesting sources of renewable energy. However, the higher cost of microalgae biofuel compared to that of petroleum prevented microalgae biofuel production. Therefore, the research on increasing lipid productivity from microalgae becomes more important. The lipid production source, triacylglycerol biosynthesis in microalgae requires short chain fatty acids as substrates, which are synthesized in chloroplasts. However, the transport mechanism of fatty acids from microalgae chloroplasts to cytosol remains unknown.ResultscDNAs from two homologs of the Arabidopsis fatty acid exporter 1 (FAX1) were cloned from Chlamydomonas reinhardtii and were named crfax1 and crfax2. Both CrFAXs were involved in fatty acid transport, and their substrates were mainly C16 and C18 fatty acids. Overexpression of both CrFAXs increased the accumulation of the total lipid content in algae cells, and the fatty acid compositions were changed under normal TAP or nitrogen deprivation conditions. Overexpression of both CrFAXs also increased the chlorophyll content. The MGDG content was decreased but the TAG, DAG, DGDG and other lipid contents were increased in CrFAXs overexpression strains.ConclusionThese results reveal that CrFAX1 and CrFAX2 were involved in mediating fatty acid export for lipids biosynthesis in C. reinhardtii. In addition, overexpression of both CrFAXs obviously increased the intracellular lipid content, especially the triacylglycerol content in microalgae, which provides a potential technology for the production of more biofuels using microalgae.

Highlights

In the past few decades, microalgae biofuel has become one of the most interesting sources of renewable energy
CrFAX1, Volvox carteri VcFAX and Gonium pectoral GpFAX1, were clustered into a single branch, while CrFAX2 and GpFAX2 were clustered into another individual branch
Arabidopsis AtFAX1, Brassica napus BnaFAX1 and fatty acid exporter 1 (FAX1) s from other plants were clustered in another branch (Fig. 1a; Additional file 2: Table S2)

Summary

Introduction

In the past few decades, microalgae biofuel has become one of the most interesting sources of renewable energy. The research on increasing lipid productivity from microalgae becomes more important. The lipid production source, triacylglycerol biosynthesis in microalgae requires short chain fatty acids as substrates, which are synthesized in chloroplasts. The lipid content of microalgae needs to be increased for commercial-scale production of biodiesel from microalgae [2, 3]. Increasing the lipid content in microalgae through genetic engineering techniques is needed to improve the potential commercial production of biodiesel from microalgae. Fatty acids (FAs) are uniquely synthesized in plastids, which is different from other prokaryotic and eukaryotic cells. Most of the synthesized FAs are transported to the endoplasmic reticulum (ER) for modification and lipid assembly Lipids, such as TAGs in seeds, are used for lipid mobilization, which is important for seed germination [6]. The FA β-oxidation process occurs in plant peroxisomes, and FAs import into the peroxisomes is mediated by full-size ABCD1 transporters [11,12,13]

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