Laboratoire de Physiologie Cellulaire et Végétale, Unité mixte de Recherche 5168 CNRS-CEA-INRA-Univ. Grenoble-Alpes, IRIG, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France.
Total Raffinage-Chimie, Tour Coupole, 2 Place Jean Millier, 92078 Paris La Défense, France.
Plant Physiol. 2021 Apr 2;185(3):815-835. doi: 10.1093/plphys/kiaa110.
The metabolic pathways of glycerolipids are well described in cells containing chloroplasts limited by a two-membrane envelope but not in cells containing plastids limited by four membranes, including heterokonts. Fatty acids (FAs) produced in the plastid, palmitic and palmitoleic acids (16:0 and 16:1), are used in the cytosol for the synthesis of glycerolipids via various routes, requiring multiple acyl-Coenzyme A (CoA) synthetases (ACS). Here, we characterized an ACS of the Bubblegum subfamily in the photosynthetic eukaryote Microchloropsis gaditana, an oleaginous heterokont used for the production of lipids for multiple applications. Genome engineering with TALE-N allowed the generation of MgACSBG point mutations, but no knockout was obtained. Point mutations triggered an overall decrease of 16:1 in lipids, a specific increase of unsaturated 18-carbon acyls in phosphatidylcholine and decrease of 20-carbon acyls in the betaine lipid diacylglyceryl-trimethyl-homoserine. The profile of acyl-CoAs highlighted a decrease in 16:1-CoA and 18:3-CoA. Structural modeling supported that mutations affect accessibility of FA to the MgACSBG reaction site. Expression in yeast defective in acyl-CoA biosynthesis further confirmed that point mutations affect ACSBG activity. Altogether, this study supports a critical role of heterokont MgACSBG in the production of 16:1-CoA and 18:3-CoA. In M. gaditana mutants, the excess saturated and monounsaturated FAs were diverted to triacylglycerol, thus suggesting strategies to improve the oil content in this microalga.
甘油磷脂的代谢途径在含有叶绿体的细胞中描述得很好，叶绿体由双层膜限制，但在含有由四层膜限制的质体的细胞中则不然，包括异源细胞。质体中产生的脂肪酸（FA），棕榈酸和棕榈油酸（16:0 和 16:1），通过各种途径在细胞质中用于甘油磷脂的合成，需要多种酰基辅酶 A（CoA）合成酶（ACS）。在这里，我们对光合真核生物微绿球藻中 Bubblegum 亚家族的 ACS 进行了表征，微绿球藻是一种用于生产多种应用脂质的油脂异源细胞。利用 TALE-N 进行基因组工程允许产生 MgACSBG 点突变，但没有获得敲除。点突变引发脂质中 16:1 的整体减少，磷脂中不饱和 18 碳酰基的特异性增加，以及甜菜碱脂质二酰甘油基 - 三甲 - 高丝氨酸中 20 碳酰基的减少。酰基辅酶 A 的图谱突出显示了 16:1-CoA 和 18:3-CoA 的减少。结构建模支持突变影响 FA 进入 MgACSBG 反应位点的可及性。在酰基辅酶 A 生物合成有缺陷的酵母中的表达进一步证实了点突变影响 ACSBG 活性。总的来说，这项研究支持异源细胞 MgACSBG 在 16:1-CoA 和 18:3-CoA 产生中的关键作用。在 M. gaditana 突变体中，过量的饱和和单不饱和 FAs 被转移到三酰基甘油中，因此表明了在这种微藻中提高油含量的策略。
