Submitted to: BioMed Central (BMC) Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/12/2013
Publication Date: 7/23/2013
Publication URL: http://handle.nal.usda.gov/10113/58749
Citation: Barkley, N.L., Isleib, T.G., Wang, M.L., Pittman, R.N. 2013. Genotypic effect of ahFAD2 on fatty acid seed profiles in six segregating peanut (Arachis hypogaea L.) populations. BioMed Central (BMC) Genetics. doi: 10.1186/1471-2156-14-62 14:62. Interpretive Summary: Dietary fats are essential to humans because they supply energy, help regulate body temperature, and carry fat soluble vitamins. Fatty acids are characterized by the number of carbon and hydrogen atoms along with the absence or presence of double bonds in the hydrocarbon chain. Saturated fatty acids contain no double bonds; whereas, unsaturated fatty acids have at least one or multiple double bonds. Due to the differences in chemical structure of the many different fatty acids, they all have unique properties. For example, oleic acid has a single double bond in its hydrocarbon chain which makes this fatty acid very stable. On the other hand, linoleic acid which has two double bonds in the hydrocarbon chain tends to break down which ultimately produces off flavors in oil or seeds containing oil. Therefore, oils or edible seeds containing oils are more stable if they are composed of a high amount of oleic acid and low amounts of linoleic acid. Peanut seeds and peanut oil are comprised of both oleic and linoleic fatty acids. The flavor and quality of the seed or the extracted oil is dependent on the fatty acids because a high amount of oleic acid in a peanut seed provides increased shelf life over peanuts with low levels of oleic. Traditionally, oleic acid content is measured from ground up seed using an analytical chemistry method known as gas chromatography. Previous molecular analysis however has demonstrated that two key mutations in ahFAD2 genes are required to produce high oleic peanuts. These mutations can be identified rapidly by extracting DNA and assessing if the mutations are present or not. The advantage of the molecular assay is that high oleic lines can be identified by using leaf tissue as opposed to seed slices. Thus, the goal of this work was to employ a molecular assay to rapidly assess breeding lines for specific mutations in a gene known as ahFAD2B in conjunction with evaluating fatty acid data to determine the affect of different alleles on the level of oleic acid accumulation in peanut populations.
Technical Abstract: Fatty acid composition from the oil extracted from peanut (Arachis hypogaea L.) seeds is an important quality trait because it may affect the flavor and length of storage of any resulting food products. In particular, a high ratio of oleic (C18:1) relative to linoleic (C18:2) fatty acid (O/L = 10) results in a longer shelf life. Previous reports suggest that the high oleic trait was controlled by recessive alleles of ahFAD2A and ahFAD2B, the former of which is thought to have a high frequency in US runner- and virginia-type cultivars. Functional mutations, G448A in ahFAD2A and 442insA in ahFAD2B eliminate or knock down desaturase activity and have been demonstrated to produce peanut oil with high O/L ratios. Crosses were made between high oleic and normal oleic peanuts to produce segregating populations. A total of 539 F2 progenies were randomly selected to empirically determine each ahFAD2 genotype and the resulting phenotype (fatty acid composition). Five of the six crosses segregated for the high oleic trait in a digenic fashion. The remaining cross was consistent with monogenic segregation because both parental genotypes were fixed for the ahFAD2A mutation. Segregation distortion was significant in ahFAD2A in one cross; however, the remaining crosses showed no distortion. Quantitative analyses revealed that dominance was incomplete for the wild type allele of ahFAD2, and both loci showed significant additive effects. Oleic and linoleic acid clearly displayed five unique phenotypes based on the number of ahFAD2 mutant alleles. Further, the ahFAD2 loci did exhibit pleiotropic interactions with palmitic (C16:0), oleic (C18:1), linoleic (C18:2) acids and the O/L ratio. Fatty acid levels in these progeny were affected by the parental genotype suggesting that other genes also influence fatty acid composition in peanut. As far as the authors are aware, this is the first study in which all of the nine possible ahFAD2 genotypes were quantitatively measured.