title: Overexpression of the soybean transcription factor GmDof4 significantly enhances the lipid content of Chlorella ellipsoidea.
abstract: BACKGROUND
  The 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.
  
  
  RESULTS
  We 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Jianhui
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China ; College of Life Sciences, University of Chinese Academy of Sciences, No.19A Yuquan Road, Beijing, 100049 China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Hao
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Lili
authors.initials: L
authors.lastname: Bai
authors.affiliation: Beijing Institute of Genomics, Chinese Academy of Sciences, Beichen West Road #1, Beijing, 100029 China.
authors.forename: Jin
authors.initials: J
authors.lastname: Xu
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Weibo
authors.initials: W
authors.lastname: Yin
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Liying
authors.initials: L
authors.lastname: Song
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Ling
authors.initials: L
authors.lastname: Xu
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Xuejie
authors.initials: X
authors.lastname: Guo
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Chengming
authors.initials: C
authors.lastname: Fan
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Beijing Institute of Genomics, Chinese Academy of Sciences, Beichen West Road #1, Beijing, 100029 China.
authors.forename: Jue
authors.initials: J
authors.lastname: Ruan
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Shanting
authors.initials: S
authors.lastname: Hao
authors.affiliation: State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Meilong Road #130, Shanghai, 200237 China.
authors.forename: Yuanguang
authors.initials: Y
authors.lastname: Li
authors.affiliation: USDA-ARS, FRRL, Utah State University, 695 N. 1100 E., Logan, UT 84322-6300 USA.
authors.forename: Richard R-C
authors.initials: RR
authors.lastname: Wang
authors.affiliation: Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Chaoyang District, Beijing, 100101 China.
authors.forename: Zanmin
authors.initials: Z
authors.lastname: Hu
keywords: Acetyl-coenzyme A carboxylase; Chlorella ellipsoidea; Lipid accumulation; Microalgae; RNA-seq; Transcription factor