Mapping of the loci controlling oleic and linolenic acid contents and development of fad2 and fad3 allele-specific markers in canola (Brassica napus L.)

Abstract

The quality of canola oil is determined by its constituent fatty acids such as oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3). Most canola cultivars normally produce oil with about 55-65% oleic acid and 8-12% linolenic acid. High concentrations of linolenic acid lead to oil instability and off-type flavor, while high levels of oleic acid increase oxidative stability and nutritional value of oil. Therefore, development of canola cultivars with increased oleic acid and reduced linolenic acid is highly desirable for canola oil quality. In this study, we have mapped one locus that has a major effect and one locus that has a minor effect for high oleic acid and two loci that have major effects for low linolenic acid in a doubled haploid population. The major locus for high C18:1 was proven to be the fatty acid desaturase-2 (fad2) gene and it is located on the linkage group N5; the minor locus is located on N1. One major QTL for C18:3 is the fatty acid desaturase-3 gene of the genome C (fad3c) and it is located on N14. The second major QTL resides on N4 and is the fad3a gene of the A genome. We have sequenced genomic clones of the fad2 and fad3c genes amplified from an EMS-induced mutant and a wild-type canola cultivar. A comparison of the mutant and wild-type allele sequences of the fad2 and fad3c genes revealed single nucleotide mutations in each of the genes. Detailed sequence analyses suggested mechanisms by which both the mutations can cause altered fatty acid content. Based on the sequence differences between the mutant and wild-type alleles, two single nucleotide polymorphism (SNP) markers, corresponding to the fad2 and fad3c gene mutations, were developed. These markers will be highly useful for direct selection of desirable fad2 and fad3c alleles during marker-assisted trait introgression and breeding of canola with high oleic and low linolenic acid.

Quantitative trait loci (QTLs) analysis of palm oil fatty acid composition in an interspecific pseudo-backcross from Elaeis oleifera (H.B.K.) Cortés and oil palm (Elaeis guineensis Jacq.)

“…The traits controlled by multiple genes such as palm oil composition can be deciphered using modern DNA marker technologies to implement a marker-assisted selection (MAS) for more desirable fatty acid composition, as it is already done for other oil crops like oilseed rape (Brassica napus) (Hu et al 1999(Hu et al , 2006Smooker et al 2011) soybean (Glycine max (L.) Merr.) (Wilson et al 2001;Monteros et al 2008;Ha et al 2010;Li et al 2011;Chen et al 2012) and olive (Olea europaea L.) (Poghosyan et al 1999;Hernández et al 2005;Banilas et al 2011).…”

G-to-A mutation at a 5' splice site of fad3c caused impaired splicing in a low linolenic mutant of canola (Brassica napus L.)

“…Linkage analysis with 183 doubled haploid lines derived from the cross of Quantum and DMS100 indicated that this allele-specific marker was significantly correlated to low C18:3. A high-throughput Invader ® assay detecting the SNP generated from the fad3c gene mutation clearly differentiated the homozygous mutant, homozygous wild-type and heterozygous genotypes, thus allowing specific selection of the fad3c alleles conferring low C18:3 content (Hu et al 2006).The molecular characterization of mutations in splicing site sequences in Arabidopsis provides valuable information on plant pre-mRNA splicing. As in other organisms, plant genes contain highly conserved 5Ј splice site (exon/intron junction-AG/GTAAG) and 3Ј splice site (intron/exon junction-TGCAG/G).…”

“…Two fad3 genes ( fad3a and fad3c) were reported to control linolenic content in Brassica napus, with fad3a located on linkage group N4 and fad3c on N14 (Barret et al 1999;Brunel et al 1999;Hu et al 2006). The high level of linolenic acid in canola oil is undesirable because linolenic acid is highly unsaturated and easily oxidized to cause off-flavor and rancidity of the oil, thus resulting in a shortened shelf life.…”

“…The development of canola varieties with fatty acid profile of C18:1 above 70% and C18:3 below 3.0% in oilseeds, for example, Natreon varieties, is a major objective of the canola breeding program in Dow AgroSciences. A single nucleotide mutation of ϩ1G to ϩ1A at the 5Ј splice site of intron 6 of the B. napus fad3c gene was previously identified by comparing the wild-type and high oleic mutant allele of the locus (Hu et al 2006). This mutant was developed through ethyl methanesulphonate (EMS) mutagenesis and contains reduced C18:3 content in oil seed.…”

Biofuels Get in the Fast Lane: Developments in Plant Feedstock Production and Processing

“…oxidative stability, low-temperature operability, lubricity, corrosiveness). Selection for breeding and genetic engineering approaches resulting in elevated oleic acid levels have been reported in many oilseed crops [96][97][98]. Conventional soybean lines with 80% oleic acid accompanied by a corresponding decrease in linoleic acid were obtained based on the contribution of only two genes (FAD2-1A and FAD2-1B) [99].…”