The present invention relates to compositions and methods for preparing poly-unsaturated long chain fatty acids in plants, plant parts and plant cells, such as leaves, roots, fruits and seeds. Nucleic acid sequences and constructs encoding PKS-like genes requires for the poly-unsaturated long chain fatty acid production, including the genes responsible for eicosapentenoic acid production of Shewanella putrefaciens and novel genes associated with the production docosahexenoic acid in Vibrio marinus are used to generate transgenic plants, plant parts and cells which contain and express one or more transgenes encoding one or more of the PKS-like genes associated with such long chain poly-unsaturated fatty acid production. Expression of the PKS-like genes in the plant system permits the large scale production of poly-unsaturated long chain fatty acids such as eicosapentenoic acid and docosahexonoic acid for modification of the fatty acid profile of plants, plants parts and tissues. Manipulation of the fatty acid profiles allows for the production of commercial quantities of novel plats oils and products.
