Identification of a mutant fatty acid elongase allele from zero-percent erucic acid Sinapis alba

The fae1 gene codes for KCS (beta -keto-acyl-CoA synthase), the candidate e nzyme for elongation of oleic acid to eicosenoic acid and erucic acid (C22: 1) in various oilseed species. Degenerate primers for the fae1 gene were us ed to amplify and clone fae1 gene homologs in high and zero C22:1 Sinapis a lba. Under stringent PCR conditions, a polymorphism was revealed between th e two genotypes and was mapped as a fae1 marker in an F-2 population derive d from a cross between high and zero C22:1 S. alba. The fae1 marker co-segr egated with C22:1 content and the C22:1 phenotypic locus. In addition, a se t of 11 RAPD markers for C22:1 in S. alba was identified. Cloning and seque ncing of the fae1 alleles in high and zero C22:1 S. alba revealed two amino -acid substitutions specific to zero C22:1 S. alba. The underlying nucleoti de substitution for one of the amino-acid substitutions and an adjacent sil ent nucleotide substitution were used to design primers for allele-specific amplicons for both the wild-type and zero C22:1 alleles. The two diagnosti c PCR tests are reliable selection tools to identify S. alba carrying one o r both of the wild-type and mutant C22:1 alleles of the KCS gene.