The control of seed oil polyunsaturate content in the polyploid crop species Brassica napus

Abstract

Many important plant species have polyploidy in their recent ancestry, complicating inferences about the genetic basis of trait variation. Although the principal locus controlling the proportion of polyunsaturated fatty acids (PUFAs) in seeds of Arabidopsis thaliana is known (fatty acid desaturase 2; FAD2), commercial cultivars of a related crop, oilseed rape (Brassica napus), with very low PUFA content have yet to be developed. We showed that a cultivar of oilseed rape with lower than usual PUFA content has non-functional alleles at three of the four orthologous FAD2 loci. To explore the genetic basis further, we developed an ethyl methanesulphonate mutagenised population, JBnaCAB_E, and used it to identify lines that also carried mutations in the remaining functional copy. This confirmed the hypothesised basis of variation, resulting in an allelic series of mutant lines showing a spectrum of PUFA contents of seed oil. Several lines had PUFA content of ~6 % and oleic acid content of ~84 %, achieving a long-standing industry objective: very high oleic, very low PUFA rapeseed without the use of genetic modification technology. The population contains a high rate of mutations and represents an important resource for research in B. napus.

Keywords: Brassica; Desaturation; EMS; Fatty acid biosynthesis; Oleic acid; Polyunsaturated fatty acids.

Fig. 1

Distribution of oleic acid and 18-carbon polyunsaturated fatty acid composition of seeds in mutant and control lines. a Oleic acid (C18:1), b total 18-carbon polyunsaturated fatty acid (Total C18 PUFA) in seeds of B. napus variety Cabriolet (Cab), BnaA.FAD2.a mutated lines (Mutant), outsegregant lines (Null) and a commercial high oleic, low linolenic line (V141)

Fig. 2

Phenotypic effects of altering amino acids in the desaturase encoded at BnaC.FAD2.a. Red mutation results in polyunsaturated fatty acid content below 7 % and oleic acid content over 80 %. Blue mutation results in fatty acid composition similar to wild type. Orange mutation results in intermediate fatty acid composition. The amino acid position mutated to a stop codon in line M0643 is boxed