Lipid metabolites in seeds of diverse Gossypium accessions: molecular identification of a high oleic mutant allele

Genetically diverse cottonseeds show altered compositions and spatial distributions of phosphatidylcholines and triacylglycerols. Lipidomics profiling led to the discovery of a novel FAD2 - 1 allele, fad2 - 1D - 1 , resulting in a high oleic phenotype. The domestication and breeding of cotton for elite, high-fiber cultivars have led to reduced variation of seed constituents within currently cultivated upland cotton genotypes. However, a recent screen of the genetically diverse U.S. National Cotton Germplasm Collection identified Gossypium accessions with marked differences in seed oil and protein content. Here, several of these accessions representing substantial variation in seed oil content were analyzed for quantitative and spatial differences in lipid compositions by mass spectrometric approaches. Results indicate considerable variation in amount and spatial distribution of pathway metabolites for triacylglycerol biosynthesis in embryos across Gossypium accessions, suggesting that this variation might be exploited by breeders for seed composition traits. By way of example, these lipid metabolite differences led to the identification of a mutant allele of the D-subgenome homolog of the delta-12 desaturase (fad2-1D-1) in a wild accession of G. barbadense that has a high oil and high oleic seed phenotype. This mutation is a 90-bp insertion in the 3' end of the FAD2-1D coding sequence and a modification of the 3' end of the gene beyond the coding sequence leading to the introduction of a premature stop codon. Given the large amounts of cottonseed produced around the world that is currently not processed into higher value products, these efforts might be one avenue to raise the overall value of the cotton crop for producers.

Characterization of the FAD2 Gene Family in Soybean Reveals the Limitations of Gel-Based TILLING in Genes with High Copy Number

Soybean seed oil typically contains 18-20% oleic acid. Increasing the content of oleic acid is beneficial for health and biodiesel production. Mutations in FAD2-1 genes have been reported to increase seed oleic acid content. A subset of 1,037 mutant families from a mutagenized soybean cultivar (cv.) Forrest population was screened using reverse genetics (TILLING) to identify mutations within FAD2 genes. Although no fad2 mutants were identified using gel-based TILLING, four fad2-1A and one fad2-1B mutants were identified to have high seed oleic acid content using forward genetic screening and subsequent target sequencing. TILLING has been successfully used as a non-transgenic reverse genetic approach to identify mutations in genes controlling important agronomic traits. However, this technique presents limitations in traits such as oil composition due to gene copy number and similarities within the soybean genome. In soybean, FAD2 are present as two copies, FAD2-1 and FAD2-2. Two FAD2-1 members: FAD2-1A and FAD2-1B; and three FAD2-2 members: FAD2-2A, FAD2-2B, and FAD2-2C have been reported. Syntenic, phylogenetic, and in silico analysis revealed two additional members constituting the FAD2 gene family: GmFAD2-2D and GmFAD2-2E, located on chromosomes 09 and 15, respectively. They are presumed to have diverged from other FAD2-2 members localized on chromosomes 19 (GmFAD2-2A and GmFAD2-2B) and 03 (GmFAD2-2C). This work discusses alternative solutions to the limitations of gel-based TILLING in functional genomics due to high copy number and multiple paralogs of the FAD2 gene family in soybean.

A case study on the genetic origin of the high oleic acid trait through FAD2-1 DNA sequence variation in safflower (Carthamus tinctorius L.)

The safflower (Carthamus tinctorius L.) is considered a strongly domesticated species with a long history of cultivation. The hybridization of safflower with its wild relatives has played an important role in the evolution of cultivars and is of particular interest with regards to their production of high quality edible oils. Original safflower varieties were all rich in linoleic acid, while varieties rich in oleic acid have risen to prominence in recent decades. The high oleic acid trait is controlled by a partially recessive allele ol at a single locus OL. The ol allele was found to be a defective microsomal oleate desaturase FAD2-1. Here we present DNA sequence data and Southern blot analysis suggesting that there has been an ancient hybridization and introgression of the FAD2-1 gene into C. tinctorius from its wild relative C. palaestinus. It is from this gene that FAD2-1Δ was derived more recently. Identification and characterization of the genetic origin and diversity of FAD2-1 could aid safflower breeders in reducing population size and generations required for the development of new high oleic acid varieties by using perfect molecular marker-assisted selection.