Biosynthetic and Regulatory Mechanisms of Steroids in Microalgae

    Figure 1. Features of biosynthetic pathway of steroids in the oleaginous alga Nannochloropsis oceanica

        Sterols are vital components of all eukaryotic cells. However, little is known about the roles, biosynthesis, and regulation of sterols in microalgae. A joint research team led by Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences (CAS-QIBEBT) and Centre of Excellence in Plant Energy Biology, University of Western Australia (UWA) has now reported the unique sterol biosynthetic pathway and revealed co-regulation of sterol production and fatty acid (FA) synthesis in an oleaginous microalga. This work appeared in Biotechnology for Biofuels (Lu, et al, Biotech Biofuels, 2014).  

        Nannochloropsis spp. are a group of wild oleaginous microalgae that are widely distributed in the oceans and are cultivated world-wide. Dr. LU Yandu from Single-Cell Center, CAS-QIBEBT, Dr. ZHOU Wenxu from UWA and their colleagues found that N. oceanica exhibits features of both higher plants and mammals (Figure 1). Temporal tracking of sterol profiles and sterol-biosynthetic transcripts in response to changes in light intensity and nitrogen supply reveal that sterols play roles in cell proliferation, chloroplast differentiation and photosynthesis.  

        Furthermore, the dynamics of FA and FA-biosynthetic transcripts upon chemical inhibitor-induced sterol depletion reveal possible co-regulation of sterol production and FA synthesis. A feedback regulation of sterol and FA homeostasis is proposed, with the 1-deoxy-D-xylulose 5-phosphate synthase (DXS, the committed enzyme in isoprenoid and sterol biosynthesis) gene potentially subject to feedback regulation by sterols. Together with molecular model of oil synthesis in N. oceanica proposed by this research team (Li, et al, Plant Cell, 2014), the sterol-dependent fatty acid regulatory mechanism discovered here suggests new genetic engineering or chemical biology approaches for enhanced oil production in microalgae. 

        This research was supported by the National Basic Research Program, and the International Innovation Partnership Program from the Chinese Academy of Sciences. Prof. XU Jian from Single Cell Center, QIBEBT and Steven M Smith from Centre of Excellence in Plant Energy Biology, UWA led the study. 



    Regulation of the cholesterol biosynthetic pathway and its integration with fatty acid biosynthesis in the oleaginous microalga Nannochloropsis oceanica, Biotechnology for Biofuels 2014, 7:81. doi:10.1186/1754-6834-7-81


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