The Roles of Cullins E3 Ubiquitin Ligases in the Lipid Biosynthesis of the Green Microalgae <i>Chlamydomonas reinhardtii</i>

• Main Authors: Qiulan Luo, Xianghui Zou, Chaogang Wang, Yajun Li, Zhangli Hu
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: International Journal of Molecular Sciences
• Subjects: <i>Chlamydomonas reinhardtii</i>; cullin; lipid metabolic; RNA inference; fatty acid
• Online Access: https://www.mdpi.com/1422-0067/22/9/4695

Microalgae-based biodiesel production has many advantages over crude oil extraction and refinement, thus attracting more and more concern. Protein ubiquitination is a crucial mechanism in eukaryotes to regulate physiological responses and cell development, which is highly related to algal biodiesel production. Cullins as the molecular base of cullin-RING E3 ubiquitin ligases (CRLs), which are the largest known class of ubiquitin ligases, control the life activities of eukaryotic cells. Here, three cullins (CrCULs) in the green microalgae <i>Chlamydomonas reinhardtii</i> were identified and characterized. To investigate the roles of CrCULs in lipid metabolism, the gene expression profiles of <i>CrCUL</i>s under nutrition starvation were examined. Except for down-regulation under nitrogen starvation, the <i>CrCUL3</i> gene was induced by sulfur and iron starvation. <i>CrCUL2</i> seemed insensitive to nitrogen and sulfur starvation because it only had changes after treatment for eight days. <i>CrCUL4</i> exhibited an expression peak after nitrogen starvation for two days but this declined with time. All <i>CrCUL</i>s expressions significantly increased under iron deficiency at two and four days but decreased thereafter. The silencing of <i>CrCUL2</i> and <i>CrCUL4</i> expression using RNAi (RNA interference) resulted in biomass decline and lipids increase but an increase of 20% and 28% in lipid content after growth for 10 days, respectively. In <i>CrCUL2</i> and <i>CrCUL4</i> RNAi lines, the content of fatty acids, especially C16:0 and C18:0, notably increased as well. However, the lipid content and fatty acids of the <i>CrCUL3</i> RNAi strain slightly changed. Moreover, the subcellular localization of CrCUL4 showed a nuclear distribution pattern. These results suggest CrCUL2 and CrCUL4 are regulators for lipid accumulation in <i>C. reinhardtii</i>. This study may offer an important complement of lipid biosynthesis in microalgae.