Identification of Transcription Factors and the Regulatory Genes Involved in Triacylglycerol Accumulation in the Unicellular Red Alga Cyanidioschyzon merolae.

Sota Takahashi,Yu Kanesaki,Sousuke Imamura,Kan Tanaka,Baifeng Zhou,Riho Okubo,Satoru Watanabe,Kazuhiro Takaya

doi:10.3390/plants10050971

Abstract

Microalgal triacylglycerols (TAGs) are a good feedstock for liquid biofuel production. Improving the expression and/or function of transcription factors (TFs) involved in TAG accumulation may increase TAG content; however, information on microalgae is still lacking. In this study, 14 TFs in the unicellular red alga Cyanidioschyzon merolae were identified as candidate TFs regulating TAG accumulation using available transcriptome and phosphoproteome data under conditions driving TAG accumulation. To investigate the roles of these TFs, we constructed TF-overexpression strains and analyzed lipid droplet (LD) formation and TAG contents in the cells grown under standard conditions. Based on the results, we identified four TFs involved in LD and TAG accumulation. RNA-Seq analyses were performed to identify genes regulated by the four TFs using each overexpression strain. Among the TAG biosynthesis-related genes, only the gene encoding the endoplasmic reticulum-localized lysophosphatidic acid acyltransferase 1 (LPAT1) was notably increased among the overexpression strains. In the LPAT1 overexpression strain, TAG accumulation was significantly increased compared with the control strain under normal growth conditions. These results indicate that the four TFs positively regulate TAG accumulation by changing their target gene expression in C. merolae.

Highlights

IntroductionMicroalgae store energy in the form of storage molecules, such as neutral lipids that form cytoplasmic lipid droplets (LDs)
We demonstrate that one of the rate-limiting steps for TAG accumulation in this alga is catalyzed by endoplasmic reticulum (ER)-localized lysophosphatidic acid acyltransferase, which is regulated by the transcription factors (TFs)
We identified four TFs involved in TAG accumulation; via the analysis of their target genes, we demonstrated that overexpression of ER-localized lysophosphatidic acid acyltransferase 1 (LPAT1) leads to TAG accumulation under normal growth conditions in C. merolae

Summary

Introduction

Microalgae store energy in the form of storage molecules, such as neutral lipids that form cytoplasmic lipid droplets (LDs). The accumulated lipid is mainly in the form of triacylglycerols (TAGs), which can be harnessed for biofuel production, and the carbons of TAGs originate from the fixed CO2 via photosynthesis. Algal-based biofuels represent an important potential renewable energy system that could contribute to solving global warming [1,2,3]. Large-scale industrial biofuel production systems using algae have not been constructed. A major reason for this is a lack of understanding of the underlying molecular mechanisms that control TAG accumulation in microalgae

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Results

Conclusion