Mapping and cloning of FAD2 gene to develop allele-specific PCR for oleic acid in spring turnip rape (Brassica rapa ssp. oleifera)

The previously identified QTL for oleic acid content observed in an Fz population from the Brassica mpn ssp. oleifera cross Jo4002 x Jo4072 (a high-oleic-acid individual) was mapped more precisely by adding markers to the linkage group which harbours the locus. In addition, the fad2 gene, which is known to encode the 18:1 desaturase in Arabidopsis, was mapped in Brassica, too. The results are consistent with the QTL corresponding to the Arabiciopsis fad2 gene. Comparison of the wild-type and high-oleic-acid allele of the locus revealed only one difference in their nucleic acid sequences leading to an amino acid change. This substitution of leucine by proline most likely affects the fold of the protein and thereby activity of the enzyme. Using this base difference, an allele-specific PCR was designed. The allele-specific markers will be very effective in selection for plants with high-oleic-acid content derived from Jo4072 because they are located exactly at the locus and can differentiate between homo- and heterozygotes.