Guéguen Nolwenn, Le Moigne Damien, Amato Alberto, Salvaing Juliette, Maréchal Eric
Laboratoire de Physiologie Cellulaire et Végétale, INRAE, CNRS, CEA, IRIG, CEA Grenoble, Université Grenoble Alpes, Grenoble, France.
Front Plant Sci. 2021 Apr 22;12:639276. doi: 10.3389/fpls.2021.639276. eCollection 2021.
The Heterokonta or Stramenopile phylum comprises clades of unicellular photosynthetic species, which are promising for a broad range of biotechnological applications, based on their capacity to capture atmospheric CO via photosynthesis and produce biomolecules of interest. These molecules include triacylglycerol (TAG) loaded inside specific cytosolic bodies, called the lipid droplets (LDs). Understanding TAG production and LD biogenesis and function in photosynthetic stramenopiles is therefore essential, and is mostly based on the study of a few emerging models, such as the pennate diatom and eustigmatophytes, such as and species. The biogenesis of cytosolic LD usually occurs at the level of the endoplasmic reticulum. However, stramenopile cells contain a complex plastid deriving from a secondary endosymbiosis, limited by four membranes, the outermost one being connected to the endomembrane system. Recent cell imaging and proteomic studies suggest that at least some cytosolic LDs might be associated to the surface of the complex plastid, via still uncharacterized contact sites. The carbon length and number of double bonds of the acyl groups contained in the TAG molecules depend on their origin. synthesis produces long-chain saturated or monounsaturated fatty acids (SFA, MUFA), whereas subsequent maturation processes lead to very long-chain polyunsaturated FA (VLC-PUFA). TAG composition in SFA, MUFA, and VLC-PUFA reflects therefore the metabolic context that gave rise to the formation of the LD, either via an early partitioning of carbon following FA synthesis and/or a recycling of FA from membrane lipids, e.g., plastid galactolipids or endomembrane phosphor- or betaine lipids. In this review, we address the relationship between cytosolic LDs and the complex membrane compartmentalization within stramenopile cells, the metabolic routes leading to TAG accumulation, and the physiological conditions that trigger LD production, in response to various environmental factors.
不等鞭毛类或硅藻门包括单细胞光合物种的进化枝，基于它们通过光合作用捕获大气中二氧化碳并产生感兴趣的生物分子的能力，在广泛的生物技术应用中具有潜力。这些分子包括装载在特定胞质体（称为脂滴，LDs）中的三酰甘油（TAG）。因此，了解光合不等鞭毛类中TAG的产生以及LD的生物发生和功能至关重要，并且主要基于对一些新兴模型的研究，例如羽纹硅藻和等鞭金藻，如 和 物种。胞质LD的生物发生通常发生在内质网水平。然而，不等鞭毛类细胞含有一个源自二次内共生的复杂质体，由四层膜限制，最外层与内膜系统相连。最近的细胞成像和蛋白质组学研究表明，至少一些胞质LD可能通过仍未表征的接触位点与复杂质体的表面相关联。TAG分子中所含酰基的碳链长度和双键数量取决于它们的来源。 合成产生长链饱和或单不饱和脂肪酸（SFA，MUFA），而随后的成熟过程导致极长链多不饱和脂肪酸（VLC-PUFA）。因此，SFA、MUFA和VLC-PUFA中的TAG组成反映了导致LD形成的代谢背景，这是通过FA 合成后碳的早期分配和/或从膜脂（例如质体半乳糖脂或内膜磷酸或甜菜碱脂）中回收FA实现的。在这篇综述中，我们探讨了不等鞭毛类细胞中胞质LD与复杂膜区室化之间的关系、导致TAG积累的代谢途径以及响应各种环境因素触发LD产生的生理条件。
