Le Moigne Damien, Carletti Marta, Amari Chems, Bonnarde Rachel, Richard Fabien, Albrieux Catherine, Mahieu Mégane, Arrighi Matteo, Si-Larbi Grégory, Jouneau Pierre-Henri, Gros Valérie, Louwagie Mathilde, Roy Sylvaine, Gong Yangmin, Pan Yufang, Hu Hanhua, Bastien Olivier, Jouhet Juliette, Amato Alberto, Maréchal Eric, Salvaing Juliette
Laboratoire de Physiologie Cellulaire et Végétale, Commissariat à l'Energie Atomique et aux Energies Alternatives, Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement, Centre National de la Recherche Scientifique, Université Grenoble Alpes; IRIG, CEA-Grenoble, 17 rue des Martyrs, 38000, Grenoble, France.
CPCV, Department of Chemistry, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005, Paris, France.
New Phytol. 2025 Sep;247(5):2245-2269. doi: 10.1111/nph.70350. Epub 2025 Jul 7.
Diatoms are a major phylum of microalgae, playing crucial ecological roles. They derive from secondary endosymbiosis, leading to a complex intracellular architecture. Their ability to store oil in lipid droplets (LDs) upon unfavourable conditions has raised interest for applications, in particular biofuels, yet Lipid Droplet (LD) biogenesis mechanisms in these organisms remain poorly understood. Here, we functionally characterize the homolog of Seipin, a major actor of LD biogenesis, in Phaeodactylum tricornutum. We used an in silico approach to analyze the evolutionary origin of PtSeipin and its specific features. Then, we used a functional genetics approach with a combination of confocal and electronic microscopy and lipidomics to characterize the protein function. We provide evidence that Stramenopiles Seipins were inherited from the host during secondary endosymbiosis. The localization of PtSeipin highlights participation of the plastid's most external membrane in LD biogenesis. Finally, the knock-out (KO) of PtSeipin leads to a strong increase of triacylglycerol (TAG) accumulation, a feature that had not been observed in adipogenic or oleaginous cells and is greatly enhanced following high light exposure. Our results suggest a redirection of lipid fluxes toward TAG synthesis, reduced TAG recycling or a combination of both in PtSeipin KO.
硅藻是微藻的一个主要门类，发挥着关键的生态作用。它们起源于二次内共生，导致了复杂的细胞内结构。它们在不利条件下能够在脂滴（LDs）中储存油脂，这引发了人们对其应用的兴趣，特别是生物燃料方面，然而这些生物体中脂滴（LD）的生物发生机制仍知之甚少。在这里，我们对三角褐指藻中脂滴生物发生的主要参与者Seipin的同源物进行了功能表征。我们使用计算机模拟方法分析了PtSeipin的进化起源及其特定特征。然后，我们采用功能遗传学方法，结合共聚焦显微镜、电子显微镜和脂质组学来表征该蛋白质的功能。我们提供的证据表明，不等鞭毛类的Seipins是在二次内共生期间从宿主那里继承而来的。PtSeipin的定位突出了质体最外层膜在脂滴生物发生中的参与。最后，PtSeipin的敲除（KO）导致三酰甘油（TAG）积累大幅增加，这一特征在脂肪生成细胞或产油细胞中未曾观察到，并且在高光照射后会大大增强。我们的结果表明，在PtSeipin敲除的情况下，脂质通量重新导向TAG合成、TAG循环减少或两者兼而有之。
