Overexpression of the soybean transcription factor GmDof4 significantly enhances the lipid content of Chlorella ellipsoidea

Abstract

BackgroundThe lipid content of microalgae is regarded as an important indicator for biodiesel. Many attempts have been made to increase the lipid content of microalgae through biochemical and genetic engineering. Significant lipid accumulation in microalgae has been achieved using biochemical engineering, such as nitrogen starvation, but the cell growth was severely limited. However, enrichment of lipid content in microalgae by genetic engineering is anticipated. In this study, GmDof4 from soybean (Glycine max), a transcription factor affecting the lipid content in Arabidopsis, was transferred into Chlorella ellipsoidea. We then investigated the molecular mechanism underlying the enhancement of the lipid content of transformed C. ellipsoidea.ResultsWe constructed a plant expression vector, pGmDof4, and transformed GmDof4 into C. ellipsoidea by electroporation. The resulting expression of GmDof4 significantly enhanced the lipid content by 46.4 to 52.9%, but did not affect the growth rate of the host cells under mixotrophic culture conditions. Transcriptome profiles indicated that 1,076 transcripts were differentially regulated: of these, 754 genes were significantly upregulated and 322 genes were significantly downregulated in the transgenic strains under mixotrophic culture conditions. There are 22 significantly regulated genes (|log2 ratio| >1) involved in lipid and fatty acid metabolism. Quantitative real-time PCR and an enzyme activity assay revealed that GmDof4 significantly up-regulated the gene expression and enzyme activity of acetyl-coenzyme A carboxylase, a key enzyme for fatty acid synthesis, in transgenic C. ellipsoidea cells.ConclusionsThe hetero-expression of a transcription factor GmDof4 gene from soybean can significantly increase the lipid content but not affect the growth rate of C. ellipsoidea under mixotrophic culture conditions. The increase in lipid content could be attributed to the large number of genes with regulated expression. In particular, the acetyl-coenzyme A carboxylase gene expression and enzyme activity were significantly upregulated in the transgenic cells. Our research provides a new way to increase the lipid content of microalgae by introducing a specific transcription factor to microalgae strains that can be used for the biofuel and food industries.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0128-4) contains supplementary material, which is available to authorized users.

Transport and transcriptional regulation of oil production in plants

“…[83] GmDof4 significantly up-regulated ACCase activity and increased lipid content by up to 52% in transgenic microalgae C. ellipsoidea. [64] Synthetic soybean Dof-like TFs elevated the expression of genes involved in FA, phospholipid and glycolipid biosynthesis, such as enoyl-ACP-reductase, KASII, sulfolipid synthase, and MGD1 in transgenic C. reinhardtii. [84] …”

“…[61,62] Recently, characterization of basic leucine zippers (bZIPs), DNA binding with one finger (Dof) and MYB TFs further revealed their functions in lipid accumulation. [63,64] All these genes are expressed primarily or specifically during seed development and have a significant impact on seed oil production (Supplemental data Table 2). …”

Metabolic pathway engineering towards enhancing microalgal lipid biosynthesis for biofuel application—A review

“…To exploit the full potential of transcription factor targeted approaches, it is worthy to consider the transcription regulators of plant origin, in microalgal application for the regulation of lipid biosynthetic pathway. For instance, a significant enhancement of lipid content in Chlorella ellipsoidea was observed when Soybean GmDof4 transcription factor that affects lipid accumulation in Arabidopsis was overexpressed in the alga [114]. Other similar transcription factors regulating lipid metabolism have been studied and characterized in plants, few of which are described below.…”

Increased biomass and lipid production by continuous cultivation of Nannochloropsis salina transformant overexpressing a bHLH transcription factor

“…It has been reported that nitrogen‐responsive regulator and phosphorous starvation response 1 (PSR1) TFs play important roles in lipid accumulation (Bajhaiya, Dean, Zeef, Webster, & Pittman, ; Boyle et al, ). Other studies reported an increased lipid content in Chlamydomonas and Chlorella cells that overexpressed DNA binding with one finger (Dof)‐type TFs (Ibanez‐Salazar et al, ; Zhang et al, ). In addition, we reported that the biomass and lipid production could be improved by the overexpression of stress‐ and/or lipid‐related TFs, including Nannochloropsis salina by overexpressing a basic helix‐loop‐helix transcription factor (NsbHLH2), AtWRI1, and NsbZIP1 (Kang et al, ; Kang et al, ; Kwon et al, ).…”

“…It has been reported that nitrogen-responsive regulator and phosphorous starvation response 1 (PSR1) TFs play important roles in lipid accumulation (Bajhaiya, Dean, Zeef, Webster, & Pittman, 2016;Boyle et al, 2012). Other studies reported an increased lipid content in Chlamydomonas and Chlorella cells that overexpressed DNA binding with one finger (Dof)-type TFs (Ibanez-Salazar et al, 2014;Zhang et al, 2014).…”