Recent global marine lipidomic analysis reveals a strong relationship between ocean temperature and phytoplanktonic abundance of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are essential for human nutrition and primarily sourced from phytoplankton in marine food webs. In phytoplanktonic organisms, EPA may play a major role in regulating the phase transition temperature of membranes, while the function of DHA remains unexplored. In the oleaginous diatom Phaeodactylum tricornutum, DHA is distributed mainly on extraplastidial phospholipids, which is very different from the EPA enriched in thylakoid lipids. Here, CRISPR/Cas9-mediated knockout of delta-5 elongase (ptELO5a), which encodes a delta-5 elongase (ELO5) catalyzing the elongation of EPA to synthesize DHA, led to a substantial interruption of DHA synthesis in P. tricornutum. The ptELO5a mutants showed some alterations in transcriptome and glycerolipidomes, including membrane lipids and triacylglycerols under normal temperature (22°C), and were more sensitive to elevated temperature (28°C) than wild type. We conclude that PtELO5a-mediated synthesis of small amounts of DHA has indispensable functions in regulating membrane lipids, indirectly contributing to storage lipid accumulation, and maintaining thermomorphogenesis in P. tricornutum. This study also highlights the significance of DHA synthesis and lipid composition for environmental adaptation of P. tricornutum.

中文翻译：

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Delta-5延伸酶敲除减少了二十二碳六烯酸和脂质合成并增加了硅藻的热敏感性


最近的全球海洋脂质组学分析揭示了海洋温度与浮游植物中 omega-3 长链多不饱和脂肪酸 (LC-PUFA) 的丰度之间存在密切关系，特别是二十碳五烯酸 (EPA) 和二十二碳六烯酸 (DHA)，它们对人类营养至关重要主要来源于海洋食物网中的浮游植物。在浮游植物中，EPA 可能在调节膜的相变温度方面发挥着重要作用，而 DHA 的功能尚未被探索。在含油硅藻三角褐指藻中，DHA主要分布在质体外磷脂上，这与富含类囊体脂质的EPA有很大不同。在这里，CRISPR/Cas9 介导的 delta-5 延伸酶 (ptELO5a) 敲除（编码 delta-5 延伸酶 (ELO5)，催化 EPA 延伸以合成 DHA）导致三角藻中 DHA 合成的实质性中断。 ptELO5a突变体在常温（22°C）下表现出转录组和甘油脂组的一些改变，包括膜脂和三酰甘油，并且比野生型对升高的温度（28°C）更敏感。我们得出结论，PtELO5a 介导的少量 DHA 合成在调节膜脂、间接促进储存脂质积累和维持三角角藻的热形态发生方面具有不可或缺的功能。这项研究还强调了 DHA 合成和脂质组成对三角褐藻环境适应的重要性。