Modification of Brassica Oil Using Conventional and Transgenic Approaches

Abstract

ABSTRACTModifying the fatty acid composition of Brassica seed oil to increase its value as a nutritional or as an industrial oil has been a major objective in Brassica breeding programs worldwide. The conventional approach to fatty acid modification has explored natural or induced mutations occurring in the same plant species or close relatives within the Brassica genus. These mutations have been shown to be associated with a few enzymes in the biosynthetic pathway of the fatty acids. Several types of Brassica oil with significantly altered levels of the long chain fatty acid erucic acid (C22:1) and medium chain fatty acids such as oleic acid (C18:1) and linolenic acid (C18:3) have been developed for different end uses through conventional breeding. When the necessary genetic variation is not available within Brassica species, gene transfer by genetic transformation has been applied, as this approach is not restricted by the sexual incompatibility barrier across species. The fatty acids targeted by the transgenic approach included fatty acids with various carbon chain lengths ranging from C8 to C22, with different numbers of double bonds, and with various functional groups such as epoxy and hydroxy fatty acids. A commercial specialty oil with high level of a novel fatty acid, lauric acid (C12:0), was produced as a result of the transfer of a FatB thioesterase gene from a distantly related plant species that produces seed oil with high level of this unusual fatty acid. Considerable progress has been achieved in altering the relative levels of the fatty acids found in Brassica oils for increased health and economic benefits and in developing Brassica oils which contain other unusual fatty acids, mainly through genetic transformation. Although the use of natural or induced mutations in the fatty acid biosynthesis within Brassica remains a valid option for oil modification, the transgenic approach will play an increasingly important role in the development of Brassica oils with altered novel fatty acid composition.