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    Home > Biochemistry News > Biotechnology News > Aquatic Institute discovers a new molecule as a carbon sink in the oil-producing marine Nannochloropsis

    Aquatic Institute discovers a new molecule as a carbon sink in the oil-producing marine Nannochloropsis

    • Last Update: 2022-05-14
    • Source: Internet
    • Author: User
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      Nannochloropsis is a group of unicellular eukaryotes belonging to Eustigmatophyceae, spherical or nearly spherical
    .
    Significantly different from other eukaryotic microalgae, the species of this genus do not contain other types of chlorophyll except chlorophyll
    a
    .
    At present, the genus has seven identified species (
    N.
    gaditana
    , N.
    salina
    , N.
    oculata
    , N.
    oceanica
    , N.
    australis
    , N.
    granulata
    and N.
    limnetica
    , the first two species have been classified by the latest classification system to Microchloropsis )
    .
    They have high photosynthetic efficiency, biomass and oil (triacylglycerol, TAG) content, are rich in eicosapentaenoic acid (EPA), and are high-quality raw materials for industrial production of EPA, as well as for fish larvae and rotifers.
    bait, which has been approved as a raw material for new human food

    .
    In recent years, due to the publication of the genome sequence and the establishment of the genetic transformation system, the species of this genus have become the most potential algal species for the study of industrial oil production models

    .

     

      The research team of Hu Hanhua from the Institute of Hydrobiology, Chinese Academy of Sciences has preserved all species and many strains of this genus, and has carried out a series of basic researches on these algal strains for more than ten years
    .
    They first established an
    efficient genetic transformation system based on PCR products ( Bioscience, Biotechnology, and Biochemistry , 2014 ) and a gene knockdown system based on RNA interference ( Plant Journal , 2017 ) in all 6 marine species , and through years of efforts High-efficiency genetic transformation based on electroporation was achieved by chemical pretreatment in N.
    limnetica
    , the only freshwater alga in this genus ( World Journal of Microbiology and Biotechnology , 2019 ) .

     

      N.
    oceanica
    is one of the most commonly used model oil-producing algae species in this genus.
    Its high oil content is associated with as many as 13
    diacylglycerol acyltransferases ( DGATs )
    in its genome that are involved in TAG synthesis .
    related; in addition, its genome encodes a phospholipid : diacylglycerol acyltransferase ( PDAT ), which also catalyzes the synthesis of TAG .
    Unlike DGAT , which uses acyl - CoA as the acyl donor, PDAT usually relies on polar lipids as the acyl donor to synthesize TAG .
    Studies on model organisms such as yeast, Chlamydomonas reinhardtii, and Arabidopsis have shown that the functions of intracellular PDAT and DGAT may be evolutionarily conserved, with PDAT mainly acting under non-stress, while DGAT acting under stress .
    Nannochloropsis marine contains DGAT that act under stress and non-stress, respectively.
    What role does its
    PDAT play in lipid regulation?



     

      Recently, the research group used Nannochloropsis marine as the object to reveal the important role of PDAT in regulating lipid metabolism and pooling intracellular carbon flow, and found that cells synthesize a new carbon replacement for TAG under stress conditions.
    Storage molecule - low unsaturated acylphosphatidylethanolamine
    .
    Based on phylogenetic analysis, it was found that Nannochloropsis
    PDAT ( NoPDAT ) has a distant relationship with PDAT of other photosynthetic organisms .
    Fine mapping found that the protein is located in the outermost membrane of the chloroplast, the chloroplast endoplasmic reticulum membrane (secondary In endosymbiosis, it is derived from the host inner membrane), which also suggests that
    NoPDAT may have functional differences with other photosynthetic organisms .
    Phenotypic analysis of NoPDAT -overexpressing and knockdown algal strains revealed that NoPDAT contributed at least 30% to intracellular TAG accumulation (Figure 1 ), and its loss of function did not trigger a compensatory mechanism regulating either DGAT .


     

    Figure 1 : Cellular localization of NoPDAT ( A , green and red fluorescence are NoPDAT-eGFP fusion protein and chloroplast signal, respectively), reduction of neutral lipids ( B ) and changes in total fatty acid ( TFA ) and TAG content ( C ) due to NoPDAT knockdown ) 

      The researchers also found that mutations in NoPDAT lead to the massive accumulation of a new class of phosphatidylethanolamines ( PE ) in cells, which are associated with intracellular polyunsaturated fatty acids ( C20:4 and C20:5 ) rich in polyunsaturated fatty acids.
    Different from
    functional PE , their fatty acyl groups are low unsaturated fatty acids such as C16:0 , C16:1 or C18:1 , which are specially called " LU-PE " .
    The content of intracellular LU-PE was also significantly positively correlated with the CO concentration of the culture .
    No accumulation of LU-PE was detected in all genes related to PE synthesis and degradation pathways by overexpression or / and knockdown , suggesting that the accumulation of LU-PE may be regulated only by NoPDAT .
    In addition, the NoPDAT mutation also activated cells to synthesize plasmalogen ( PME ) , the content of which was also significantly positively correlated with CO concentration




    .
    These results indicate that the blockage of
    TAG synthesis caused by the NoPDAT mutation will cause the intracellular carbon flow to LU-PE and plasmalogen, especially under the condition of high concentration of CO 2 , LU-PE will replace TAG as the main carbon sink in the cell (Fig.
    2 ) .

     

       

    Figure 2 : Schematic diagram of NoPDAT regulating lipid metabolism in Nannochloropsis marine cells

      Plasmalogen is a special ether phospholipid present in almost all human tissues, with the highest concentration in the brain, and its deficiency is closely related to diseases of the elderly such as Alzheimer's disease
    .
    Previous studies suggested that photosynthetic organisms cannot synthesize this phospholipid

    .
    The new findings of this study provide a possible way to realize the commercial production of plasmalogen using microalgae

    .
    At present, an invention patent entitled "A method for increasing the content of microalgae plasmalogen and
    RNA interference fragments" has been authorized
    .

     

      This research was funded by the National Natural Science Foundation of China ( 41976119 ) and the Major Research Program ( 91751117 ) under the auspices of researcher Hu Hanhua, mainly by researchers from the Institute of Hydrobiology
    .
    Researchers from Peking University, the Oil Crops Research Institute of the Chinese Academy of Agricultural Sciences, the Grenoble Alpes University in France and the University of Maryland in the United States participated in part of the research work

    .
    Relevant research results were published in the journal Plant Physiology under the title of "
    PDAT regulates PE as transient carbon sink alternative to triacylglycerol in Nannochloropsis ".
    The link to the article is
    https://academic.
    oup.
    com/plphys/advance-article/doi/10.
    1093/ plphys/kiac160/6564233?login=true
    .

     

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