Peter Janick, Huleux Marie, Spaniol Benjamin, Sommer Frederik, Neunzig Jens, Schroda Michael, Li-Beisson Yonghua, Philippar Katrin
Plant Biology, Center for Human- and Molecular Biology (ZHMB), Saarland University, Saarbrücken, Germany.
Aix Marseille Univ, CEA, CNRS, Institute of Bioscience and Biotechnology of Aix Marseille, BIAM, Saint Paul-Lez-Durance, France.
Front Mol Biosci. 2022 Aug 30;9:939834. doi: 10.3389/fmolb.2022.939834. eCollection 2022.
In algae and land plants, transport of fatty acids (FAs) from their site of synthesis in the plastid stroma to the endoplasmic reticulum (ER) for assembly into acyl lipids is crucial for cellular lipid homeostasis, including the biosynthesis of triacylglycerol (TAG) for energy storage. In the unicellular green alga , understanding and engineering of these processes is of particular interest for microalga-based biofuel and biomaterial production. Whereas in the model plant , FAX (fatty acid export) proteins have been associated with a function in plastid FA-export and hence TAG synthesis in the ER, the knowledge on the function and subcellular localization of this protein family in Chlamydomonas is still scarce. Among the four FAX proteins encoded in the Chlamydomonas genome, we found Cr-FAX1 and Cr-FAX5 to be involved in TAG production by functioning in chloroplast and ER membranes, respectively. By immunolocalization, we show that Cr-FAX1 inserts into the chloroplast envelope, while Cr-FAX5 is located in ER membranes. Severe reduction of Cr-FAX1 or Cr-FAX5 proteins by an artificial microRNA approach results in a strong decrease of the TAG content in the mutant strains. Further, overexpression of chloroplast Cr-FAX1, but not of ER-intrinsic Cr-FAX5, doubled the content of TAG in Chlamydomonas cells. We therefore propose that Cr-FAX1 in chloroplast envelopes and Cr-FAX5 in ER membranes represent a basic set of FAX proteins to ensure shuttling of FAs from chloroplasts to the ER and are crucial for oil production in Chlamydomonas.
在藻类和陆地植物中，脂肪酸（FAs）从其在质体基质中的合成位点运输到内质网（ER）以组装成酰基脂质，对于细胞脂质稳态至关重要，包括用于能量储存的三酰甘油（TAG）的生物合成。在单细胞绿藻中，对于基于微藻的生物燃料和生物材料生产而言，理解和改造这些过程尤为重要。在模式植物中，FAX（脂肪酸输出）蛋白已被认为与质体FA输出功能相关，从而与内质网中的TAG合成有关，而关于衣藻中该蛋白家族的功能和亚细胞定位的知识仍然匮乏。在衣藻基因组编码的四种FAX蛋白中，我们发现Cr-FAX1和Cr-FAX5分别通过在叶绿体和内质网膜中发挥作用参与TAG的产生。通过免疫定位，我们表明Cr-FAX1插入叶绿体包膜，而Cr-FAX5位于内质网膜中。通过人工microRNA方法严重降低Cr-FAX1或Cr-FAX5蛋白会导致突变菌株中TAG含量大幅下降。此外，叶绿体Cr-FAX1的过表达而非内质网内在的Cr-FAX5的过表达使衣藻细胞中的TAG含量增加了一倍。因此，我们提出叶绿体包膜中的Cr-FAX1和内质网膜中的Cr-FAX5代表了一组基本的FAX蛋白，以确保脂肪酸从叶绿体运输到内质网，并且对于衣藻中的油脂生产至关重要。
