Cytochrome b5 (Cb5) is a haem-binding protein located in the endoplasmic reticulum (ER) and the outer mitochondrial membranes of higher eukaryotes. In higher plants, animals, and fungi, the ER resident Cb5 has been shown to play a role in desaturation of acyl CoA fatty acids. Higher plants Cb5 isoforms from plants such as soybean or Arabidopsis are capable of modulating omega-3 desaturation. Co-expression of certain Cb5 isoforms with FAD3 in a host plant results in increased production of seed oil content as well as altered ratio between different fatty acids. It is also disclosed here that overexpression of Yarrowia ACL enzymes in the plastids of a host plant helps boost the synthesis of acetyl CoA, which in turn, may lead to increased synthesis of fatty acids and enhanced oil accumulation in the seeds.