Production of eicosapentaenoic acid (EPA, 20:5n-3) in maize (Zea mays L.) through the alternative ∆8 desaturation pathway mediated by particle bombardment

Very long chain polyunsaturated fatty acids (VLCPUFAs), especially eicosapentaenoic acid (EPA, 20:5∆5,8,11,14,17) and docosahexaenoic acid (DHA, 22:6∆4,7,10,13,16,19) have demonstrated important roles in a number of aspects of human health. Currently, our primary dietary sources for these fatty acids are from marine fish. Producing VLCPUFAs in oilseed crop by metabolic engineering was considered to provide an alternative, sustainable sources. Here, three heterologous genes, ∆9 elongase (∆9-Elo) of Isochrysis galbana, ∆8 desaturase (∆8-Des) of Euglena gracilis, ∆5 desaturase (∆5-Des) of Mortierella alpina, were co-transformed into maize inbred line Qi319 using a particle bombardment transformation method to produce EPA through the alternative ∆8 desaturation synthetic pathway. A total of 144 herbicide resistant lines were obtained with an average transformation efficiency of 7.95%, of which 98 lines contain the Bar genes with the positive transformation efficiency of 4.74%. In addition, 60 of the 98 positive transgenic lines were identified to contain all three transgenes, ∆9-Elo, ∆8-Des, and ∆5-Des. The fatty acid composition of the leaves from the 60 transgenic lines were subjected to gas liquid chromatography analysis and the results showed that the amounts of EPA reached 1.99% in an individual leaf. These data demonstrate the feasibility for the heterologous production of EPA in maize and this will lay a foundation for the production of VLCPUFAs, including EPA and DHA, in maize by metabolic engineering in the future.