The carbon source of TAG synthesis in different stages and the activity changes of main metabolic pathways
Facing the two serious problems of energy shortage and environmental pollution, it is imminent to find new renewable and environmentally friendly energy sources. Microalgae energy is considered to be a promising new energy.
Nannochloropsis is a single-celled algae, widely distributed in seawater, freshwater and brackish water. It can synthesize a large amount of oil under nitrogen deficiency stress, and this stress response is one of the scientific foundations of microalgae energy.
Recently, the Single Cell Center of Qingdao Institute of Bioenergy and Processes, Chinese Academy of Sciences and the Department of Plant Biochemistry of Ruhr University in Germany collaborated to build a dynamic model of proteome under nitrogen-deficient stress for Nannochloropsis, revealing three of the stress process This physiological stage provides a new perspective for fat metabolism engineering. The result was published in "Biotechnology for Biofuels" a few days ago.
Construction of a dynamic model of Pseudococcoidea proteome
According to the researcher and Dr. Wei Li from the Single Cell Center, Nannochloropsis can store fixed solar energy and carbon dioxide in the form of triglyceride (TAG) under certain environmental conditions, with rapid growth and triglyceride content. High, rich in polyunsaturated fatty acids (PUFAs) and other advantages.
In addition, Nannochloropsis also has the ability to reduce carbon dioxide and other greenhouse gas emissions, is an important source of biofuels and biomaterials, and has broad application prospects in industrial flue gas treatment and green energy. At the same time, the genome of Nannochloropsis is small and haploid, which is convenient for genetic manipulation. Therefore, Nannochloropsis gradually became a model organism for the study of synthetic biology of eukaryotic microalgae.
The oil accumulation process of industrial oleaginous microalgae under nitrogen deficiency stress has been closely watched by the academic and industrial circles. In the past ten years, thousands of related documents have been published in professional journals at home and abroad, and many studies have made progress.
The reporter learned that the single-cell center team has achieved the customization of the oil component of Nannochloropsis by overexpressing triglyceride synthase, and overexpression of RuBisCO has increased biomass accumulation. Korean scientists have increased the lipid production of Nannochloropsis by overexpressing transcription factors by 30% to 50%. American scientists have doubled lipid production by reducing the expression of another transcription factor.
Previously, the single cell center has constructed its mechanism model on the basis of the transcriptome and metabolome. However, there are important differences in the experimental data at the transcriptome level and the metabolome level, and it is impossible to completely use gene expression to metabolic regulation. Delayed interpretation. This is because the process from transcription to metabolite changes is still regulated at the protein level. Existing research usually only involves one level of regulation, namely the overexpression or knockdown of a single gene. In fact, no matter whether it is Nannochloropsis or general oleaginous microalgae, its protein level metabolic network regulation mechanism is poorly understood.
In response to this problem, the Sino-German joint research group led by You Wuxin and Dr. Wei Li of the Single Cell Center published the time series proteome data of Nannochloropsis sp. under nitrogen deficiency stress, combined with the corresponding transcriptome and metabolome data, Using the latest statistical analysis methods, the process characteristics of triglyceride synthesis by cells under nitrogen deficiency stress are more comprehensively revealed.
The researchers found that the process can be divided into three stages. The first stage is the initial stage of nitrogen deficiency. At this time, the cell feels the lack of nitrogen in the external environment, but because there is a certain amount of nitrogen reserves in the cell, its metabolic process does not change significantly. The second stage is the middle period of nitrogen deficiency. At this stage, the nitrogen stored in the cells has been almost consumed, and the nitrogen in the amino acids needs to be recovered through protein degradation to maintain the operation of the cell's key metabolic processes. At the same time, photosynthesis and lipid metabolism are also affected to varying degrees. . The third stage is the late stage of nitrogen deficiency. The cells further increase the rate of protein degradation, and the rate of tricarboxylic acid cycle and oil synthesis is greatly increased, although the rate of photosynthesis has decreased, but it is still going on.
This revised model characterizes the nitrogen-deficient oil production process more accurately, and further proves that de novo triglyceride synthesis plays a leading role in oil accumulation, while membrane lipid recovery accounts for only a small portion of lipid accumulation.
Further improve oil and fat yield
The new model established by the research team not only provides a series of new strategies and goals for directional regulation of microalgae metabolic regulation networks to improve oil and fat yield, but also lays a research foundation for microalgae oil production to increase industrial production.
Wei Li told reporters that industrial oil-producing microalgae have received widespread attention from various countries. As far as the current industry situation is concerned, at present, the Taiwan region of my country has piloted a microalgae carbon reduction treatment project combined with a power plant; my country’s Xinao Energy Holding Company has established a commercial plant using microalgae to produce biodiesel in Inner Mongolia. On a global scale, several companies, including traditional energy producers, have established experimental bases and mid-level algae farms to produce biofuels, such as ExxonMobile in California and E.ON in Germany.
"The research on the post-translational modification (PTM) of Nannochloropsis is still blank, and the research on PTM of microalgae is rare." You Wuxin added, "We are developing this new research field to mimic the sphere Algae is a model organism, to study the PTM regulatory response mechanism in the carbon metabolism pathway of eukaryotic algae. This work helps to fill the gaps in the current research on the microalgae PTM field, and also provides for improving the carbon fixation and oil conversion capabilities of Nannochloropsis. New research direction."
Existing microalgae protein modification research methods are usually limited to the confirmation of specific residue modifications and function speculation. On the basis of the established proteome regulation model, try to dynamic analysis of protein modification under different environmental conditions, taking into account the impact of environmental factors on protein modification as one of the important factors affecting the metabolic regulation network, will be microalgae PTM research opens up new perspectives. (â– Reporter Liao Yang correspondent Liu Jia)
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