Development and characterization of low ¿-linolenic acid (BMC Genetics)

Background: Traditional canola (Brassica napus L.; AACC, 2n?=?38) cultivars yield seed oil with a relatively high proportion of ?-linolenic acid (ALA; C18:3 cis?9,12,15), which is desirable from a health perspective. Unfortunately, due to the instability of this fatty acid, elevated levels also result in oils that exhibit a short shelf life and problems associated with use at high temperatures. As a result, the development of cultivars bearing reduced amounts of ALA in their seeds is becoming a priority. To date, several low ALA B. napus cultivars (~2-3% ALA of total fatty acids) have been developed and molecular analyses have revealed that the low ALA phenotype of lines tested thus far is a result of mutations within two `class b? FATTY ACID DESATURASE 3 (FAD3) genes. Since B. napus possesses six FAD3 genes (two `class a?, two `class b? and two `class c?) and ALA levels of approximately 2-3% remain in these low ALA lines, it is likely that the mutation of additional FAD3 genes could further decrease the content of this fatty acid. Results: In this study, we generated low ALA (?2%) lines of B. oleracea, which is the C genome progenitor species of B. napus, via ethyl methanesulphonate (EMS) mutagenesis. We identified a novel nonsense mutation within the `class a? FAD3 gene (BoFAD3-2) in these lines, which would result in the production of an encoded protein lacking 110 amino acids at its C terminus. When expressed in Saccharomyces cerevisiae, this mutant protein exhibited a drastic decline in its ?-15 desaturase activity compared to the wild-type (wt) protein. Furthermore, we demonstrated that the expression of the mutant BoFAD3-2 gene was significantly reduced in developing seeds of low ALA lines when compared to expression in wt plants. Conclusions: Given the additive nature of FAD3 mutations on ALA content and the ease with which B. napus can be re-synthesized from its progenitor species, the mutant isolated here has the potential to be used for the future development of B. napus cultivars exhibiting further reductions in ALA content.