Delta-5 elongase knockout reduces DHA and TAG synthesis coupled with an increase of heat sensitivity in a marine diatom

Abstract

AbstractRecent global marine lipidomic analysis reveals a strong relationship in the ocean between 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 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 to be explored. In the oleaginous diatomPhaeodactylum tricornutum, DHA is distributed mainly on extraplastidial phospholipids, which is very different from the EPA enriched in thylakoid lipids. Here, CRISPR/Cas9-mediated knockout ofptELO5a, which encodes a delta-5 elongase catalyzing the elongation of EPA to synthesize DHA, led to a substantial interruption of DHA synthesis inP. tricornutum. TheptELO5amutants show significant alterations in transcriptome and glycerolipidomes including membrane lipids and triacylglycerols under normal temperature (22°C), and are more sensitive to elevated temperature (28°C) than wild type. We conclude that the PtELO5a-mediated synthesis of small amounts of DHA has indispensable functions in regulating the membrane lipid, and indirectly contributing storage lipid accumulation and maintaining thermomorphogenesis inP. tricornutum. This study also highlights the significance of DHA synthesis and lipid composition for environmental adaptation ofP. tricornutum.