The oil production process of Nannochloropsis sp. under nitrogen deficiency conditions. In the figure, each cell is a Nannochloropsis cell, the time represents the number of days after the onset of nitrogen deficiency induction, and the green color is a neutral lipid (mostly triglyceride) stained with Bodipy dye.

Some of the microalgae in nature are considered to be important new energy crops because of their high oil production, rapid growth, and strong environmental adaptability. They can be cultivated on marginal lands using seawater or wastewater, but they are currently high in oil production. The mechanism of metabolism and regulation is not yet clear. Recently, the research team led by the Single Cell Research Center of the Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, took the lead in revealing the dynamics of the oil production process at the molecular level. The related results were published online on April 1 in Plant Cell (Li, et al, Plant Cell, 2014).

In the previous study, the team used the microalgae as a research model to reveal the genetic basis and evolution of the high-oil-producing traits of microalgae (Wang, et al, PLoS Genetics, 2014). However, how does the process of efficiently synthesizing triglyceride (algae oil) at the molecular level occur? This core issue has been lacking in support of systematic experimental evidence.

Through the use of high-precision transcriptomics and lipidomics analysis methods, Dr. Li Jing, Dr. Wang Dongmei, Dr. Ning Kang and Dr. Han Danxiang of Arizona State University at the Single Cell Research Center of Qingdao Energy Research Institute examined the nitrogen deficiency of Nannochloropsis sp. The dynamic changes of transcriptome and lipid metabolomes at six different time points from 3 hours to 48 hours during the process of oil production were induced, and the dynamic model of oil production from wild oilseeds was firstly established in the world. In the absence of nitrogen sources, TAG content in algae cells increased significantly and membrane lipid content decreased.

At the transcriptional level, transcript levels of related genes such as glycolysis, PDHC and PDHC shunts, mitochondrial Krebs cycle and oxidation pathways, and specific transporters are upregulated, promoting carbon flow from carbohydrates, proteins, and membrane lipids. Metabolic pathways flow toward glyceride synthesis. In the TAG assembly pathway, seven DGAT genes located in different organelles, such as chloroplasts, mitochondria, and cytoplasm, were up-regulated at the time of nitrogen deficiency, and together with other up-regulated genes in the upstream, promoted the synthesis of a large number of TAGs. The dual elucidation mechanism of microalgae subcellular level temporal and spatial lipid anabolism explained in this study provides an important theoretical basis and new research ideas for high-yielding oilseed genetic engineering breeding.

This first molecular dynamic model of oil production by microalgae also further revealed the difference in the global transcriptional regulation of oil synthesis between wild high-yield oilseeds such as Nannochloropsis and low-yield Chlamydomonas reinhardtii. Among them, the former has a Type I fatty acid synthase gene, and at the same time, its absolute abundance of the DGAT gene (catalogue of the last step of triglyceride synthesis) is more than twice that of the latter. Therefore, the former not only has the largest number of DGAT genes (13), but also has the largest number of known algae and plant genomes, and reserves a large amount of DGAT transcripts in both nitrogen-deficient and non-nitrogen-deficient conditions, thereby efficiently supporting a large amount of lipids. accumulation.

The study was supported by the fund's major international cooperation projects, the "973" Ministry of Science and Technology, and the International Partner Program of the Chinese Academy of Sciences Innovation Team, Xu Jian, a researcher at the Single Cell Research Center of the Qingdao Energy Institute of the Chinese Academy of Sciences and the Institute of Hydrobiology, Chinese Academy of Sciences. Researcher Hu Qiang of the Energy Research and Development Center co-chaired the project.

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