Laboratoire de Physiologie Cellulaire et Végétale, CNRS, CEA, INRA, Université Grenoble Alpes, Institut de Recherche Interdisciplinaire de Grenoble, CEA Grenoble, 17 avenue des Martyrs, 38000, Grenoble, France.
MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI, 48824, USA.
Biochimie. 2020 Feb;169:3-11. doi: 10.1016/j.biochi.2019.07.005. Epub 2019 Jul 7.
Diatoms are a phylum of unicellular photosynthetic eukaryotes living in oceans and fresh waters, characterized by the complexity of their plastid, resulting from a secondary endosymbiosis event. In the model diatom Phaeodactylum tricornutum, fatty acids (FAs) are synthesized from acetyl-CoA in the stroma of the plastid, producing palmitic acid. FAs are elongated and desaturated to form very-long chain polyunsaturated fatty acids (VLC-PUFAs) in domains of the endomembrane system that need to be identified. Synthesis of VLC-PUFAs is coupled with their import to the core of the plastid via the so-called "omega" pathway. The biosynthesis of sterols in diatoms is likely to be localized in the endoplasmic reticulum as well as using precursors deriving from the mevalonate pathway, using acetyl-CoA as initial substrate. These metabolic modules can be characterized functionally by genetic analyzes or chemical treatments with appropriate inhibitors. Some 'metabolic modules' are characterized by a very low level of metabolic intermediates. Since some chemical treatments or genetic perturbation of lipid metabolism induce the accumulation of these intermediates, channeling processes are possibly involved, suggesting that protein-protein interactions might occur between enzymes within large size complexes or metabolons. At the junction of these modules, metabolic intermediates might therefore play dramatic roles in directing carbon fluxes from one direction to another. Here, acetyl-CoA seems determinant in the balance between TAGs and sterols. Future lines of research and potential utilization for biotechnological applications are discussed.
硅藻是一类生活在海洋和淡水中的单细胞光合真核生物，其质体的复杂性是由于二次内共生事件而产生的。在模式硅藻三角褐指藻中，脂肪酸（FAs）是在质体基质中由乙酰辅酶 A 合成的，产生棕榈酸。FAs 在需要鉴定的内膜系统域中被延长和去饱和，形成非常长链多不饱和脂肪酸（VLC-PUFAs）。VLC-PUFAs 的合成与其通过所谓的“ω”途径导入质体核心有关。硅藻中甾醇的生物合成可能定位于内质网中，并且使用来自甲羟戊酸途径的前体，以乙酰辅酶 A 作为初始底物。这些代谢模块可以通过遗传分析或用适当的抑制剂进行化学处理来在功能上进行表征。一些“代谢模块”的代谢中间产物水平非常低。由于一些化学处理或脂质代谢的遗传干扰会导致这些中间产物的积累，因此可能涉及到通道化过程，这表明酶之间的蛋白质-蛋白质相互作用可能发生在大型复合物或代谢物中。在这些模块的交界处，代谢中间产物可能在将碳通量从一个方向引导到另一个方向方面发挥重要作用。在这里，乙酰辅酶 A 似乎在 TAG 和甾醇之间的平衡中起决定性作用。讨论了未来的研究方向和潜在的生物技术应用利用。
