Genetic alteration of soybean oil composition by a chemical mutagen

Characterization of a new GmFAD3A allele in Brazilian CS303TNKCA soybean cultivar

KEY MESSAGE

We molecularly characterized a new mutation in the GmFAD3A gene associated with low linolenic content in the Brazilian soybean cultivar CS303TNKCA and developed a molecular marker to select this mutation. Soybean is one of the most important crops cultivated worldwide. Soybean oil has 13% palmitic acid, 4% stearic acid, 20% oleic acid, 55% linoleic acid and 8% linolenic acid. Breeding programs are developing varieties with high oleic and low polyunsaturated fatty acids (linoleic and linolenic) to improve the oil oxidative stability and make the varieties more attractive for the soy industry. The main goal of this study was to characterize the low linoleic acid trait in CS303TNKCA cultivar. We sequenced CS303TNKCA GmFAD3A, GmFAD3B and GmFAD3C genes and identified an adenine point deletion in the GmFAD3A exon 5 (delA). This alteration creates a premature stop codon, leading to a truncated protein with just 207 residues that result in a non-functional enzyme. Analysis of enzymatic activity by heterologous expression in yeast support delA as the cause of low linolenic acid content in CS303TNKCA. Thus, we developed a TaqMan genotyping assay to associate delA with low linolenic acid content in segregating populations. Lines homozygous for delA had a linolenic acid content of 3.3 to 4.4%, and the variation at this locus accounted for 50.83 to 73.70% of the phenotypic variation. This molecular marker is a new tool to introgress the low linolenic acid trait into elite soybean cultivars and can be used to combine with high oleic trait markers to produce soybean with enhanced economic value. The advantage of using CS303TNKCA compared to other lines available in the literature is that this cultivar has good agronomic characteristics and is adapted to Brazilian conditions.

Soybean (Glycine max) Mutant and Germplasm Resources: Current Status and Future Prospects

Genetic bottlenecks during domestication and modern breeding limited the genetic diversity of soybean (Glycine max (L.) Merr.). Therefore, expanding and diversifying soybean genetic resources is a major priority for the research community. These resources, consisting of natural and induced genetic variants, are valuable tools for improving soybean and furthering soybean biological knowledge. During the twentieth century, researchers gathered a wealth of genetic variation in the forms of landraces, Glycine soja accessions, Glycine tertiary germplasm, and the U.S. Department of Agriculture (USDA) Type and Isoline Collections. During the twenty-first century, soybean researchers have added several new genetic and genomic resources. These include the reference genome sequence, genotype data for the USDA soybean germplasm collection, next-generation mapping populations, new irradiation and transposon-based mutagenesis populations, and designer nuclease platforms for genome engineering. This paper briefly surveys the publicly accessible soybean genetic resources currently available or in development and provides recommendations for developing such genetic resources in the future. © 2016 by John Wiley & Sons, Inc.

Genotype x Environment Interactions, Stability, and Agronomic Performance of Soybean with Altered Fatty Acid Profiles

There has been a major effort to produce soybean [Glycine max (L.) Merr.] lines with modified fatty acid profiles in order to improve quality and develop new uses for soybean oil. Utilization of the lines depends on their agronomic traits and stability of the fatty acid profiles in diverse environments. The objectives of this study were to (i) evaluate the influence of years and locations on the fatty acid composition of soybean genotypes with unique fatty acid profiles, (ii) determine which fatty acids and fatty acid profiles are the most stable, and (iii) evaluate agronomic and seed quality traits of mutant soybean lines. Genotypes were evaluated over three years (1996, 1997, and 1998) at four locations in Southern Ontario, Canada. Year effects had the largest impact on all fatty acid levels. Location effects were significant only for oleic and linolenic acids. Genotype x year interaction effect was significant for all fatty acids whereas genotype x location and genotype x year x location interaction effects were significant only for oleic, linoleic, and linolenic acids. Mutants with reduced or elevated palmitic, elevated oleic, or reduced linolenic acid concentrations exhibited average or higher stability than lines with normal levels of these fatty acids. Therefore, these lines may be suitable for growing in a wide range of environments. Maturity, plant height, lodging, seed size, and seed quality were significantly different between mutants and cultivars. Seed yield was significantly reduced in mutants compared to cultivars.

Soybean genetic resources and crop improvement

The soybean (Glycine max (L.) Merr.) is an economically important leguminous crop for feed, oil, and soyfood products. It contains about 40% protein and 20% oil in the seed and, in the international trade markets, is ranked number one in oil production (48%) among the major oil seed crops. Despite its economic importance, the genetic base of soybean cultivars is extremely narrow. The indigenous cultivars and landraces in East Asia are on the verge of extinction, because farmers are now growing high yielding soybean cultivars. The exotic germplasm, enriched with genes for abiotic and biotic stresses, has not been fully exploited by soybean breeders. Mutation breeding has improved the fatty acids of the soybeans and has produced soybeans tolerant to herbicides. By using recombinant DNA technology, Monsanto has produced stable glyphosate tolerant soybean lines known as 'Round Up Ready' soybean. DuPont is producing transgenic soybean lines with improved fatty acids content. The feasibility of developing hybrid soybeans is still an open question.Key words: soybean, Glycine spp., exotic germplasm, mutation, interspecific hybridization, biotechnology, hybrid soybeans.

Food use and health effects of soybean and sunflower oils

This review provides a scientific assessment of current knowledge of health effects of soybean oil (SBO) and sunflower oil (SFO). SBO and SFO both contain high levels of polyunsaturated fatty acids (PUFA) (60.8 and 69%, respectively), with a PUFA:saturated fat ratio of 4.0 for SBO and 6.4 for SFO. SFO contains 69% C18:2n-6 and less than 0.1% C18:3n-3, while SBO contains 54% C18:2n-6 and 7.2% C18:3n-3. Thus, SFO and SBO each provide adequate amounts of C18:2n-6, but of the two, SBO provides C18:3n-3 with a C18:2n-6:C18:3n-3 ratio of 7.1. Epidemiological evidence has suggested an inverse relationship between the consumption of diets high in vegetable fat and blood pressure, although clinical findings have been inconclusive. Recent dietary guidelines suggest the desirability of decreasing consumption of total and saturated fat and cholesterol, an objective that can be achieved by substituting such oils as SFO and SBO for animal fats. Such changes have consistently resulted in decreased total and low-density-lipoprotein cholesterol, which is thought to be favorable with respect to decreasing risk of cardiovascular disease. Also, decreases in high-density-lipoprotein cholesterol have raised some concern. Use of vegetable oils such as SFO and SBO increases C18:2n-6, decreases C20:4n-6, and slightly elevated C20:5n-3 and C22:6n-3 in platelets, changes that slightly inhibit platelet generation of thromboxane and ex vivo aggregation. Whether chronic use of these oils will effectively block thrombosis at sites of vascular injury, inhibit pathologic platelet vascular interactions associated with atherosclerosis, or reduce the incidence of acute vascular occlusion in the coronary or cerebral circulation is uncertain. Linoleic acid is needed for normal immune response, and essential fatty acid (EFA) deficiency impairs B and T cell-mediated responses. SBO and SFO can provide adequate linoleic acid for maintenance of the immune response. Excess linoleic acid has supported tumor growth in animals, an effect not verified by data from diverse human studies of risk, incidence, or progression of cancers of the breast and colon. Areas yet to be investigated include the differential effects of n-6- and n-3-containing oil on tumor development in humans and whether shorter-chain n-3 PUFA of plant origin such as found in SBO will modulate these actions of linoleic acid, as has been shown for the longer-chain n-3 PUFA of marine oils.(ABSTRACT TRUNCATED AT 400 WORDS)

Genetic control of polyunsaturated fatty acid biosynthesis in flax (Linum usitatissimum) seed oil

The inheritance of two mutants of flax (Linum usitatissimum), having altered proportions of the C18 polyunsaturated fatty acids, linoleic and linolenic, was examined. Both lines, 'M1589' and 'M1722', are homozygous for a single gene mutation which reduces linolenic acid content from 34% to 22% and raises linoleic acid from 15% to 27%. Genetic analysis of crosses involving 'M1589', 'M1722' and their parental cultivar 'Glenelg' revealed that these mutations are in different unlinked genes and exhibit additive (codominant) gene action. The symbolsLn1 andLn2 are proposed for the mutated genes in 'M1589' and 'M1722', respectively. Recombinant genotypes homozygous for the mutant alleles at both loci are very low in linolenic acid (2%) and high in linoleic acid (48%), with unaltered proportions of other fatty acids. The complete inverse correlation between linoleic and linolenic acids (r=-0.98) indicates that the mutations block the synthesis of linolenic acid at the linoleic desaturation step.

Inheritance of low linolenic acid content of the seed oil of a mutant in Glycine max

Linolenic acid content of the oil from F1, F2, and F3 seeds was compared with the parental values from a cross between a soybean cultivar with high (7.0%) and a mutant line with low (3.4%) linolenate (18∶3). Linolenic acid content of F1 seeds was intermediate to that of selfed seeds from the two parents and values from reciprocal crosses were essentially the same. This demonstrated that in this cross, linolenic acid content of the oil was controlled by the embryo rather than by the maternal parent. The distribution of linolenic acid in F2 seeds from F1 plants was trimodal and extended across the range of parental values. High and low linolenate F2 plants bred true for 18∶3 content and the F3 distribution of seeds from F2 plants with intermediate levels of 18∶3 was similar to the F2 distribution. The data were consistent with a model for two alleles with additive effects at a single locus controlling percent linolenic acid in these progenies. The simply-inherited alleles for low linolenate could be readily transferred to agronomically superior soybean cultivars, which would improve the fatty acid composition of the oil.