Genetic regulation of elevated stearic acid concentration in soybean oil

Abstract

Soybean [Glycine max (L.) Merr.] oil from commercial cultivars typically contains ca. 3% stearic acid (18:0). However, germplasm carrying different mutations at the locus governing stearic acid (Fas) may contain 3% to about 35% 18:0. Among these germplasm, a newly developed line, FAM94-41 (9% 18:0), carries a serendipitous natural mutation that is temporarily designated as the recessive fas nc allele, and the germplasm A6 (26% 18:0) carries the recessive fas a allele. Mendelian genetic analysis of progeny from FAM94-41 × A6 revealed that fas nc and fas a are allelic to each other and represent different mutations in the same structural gene. However, the gene products (enzymes) produced by these alleles are unknown. The observation that 18:0 concentrations among progeny from FAM94-41 × A6 increased primarily at the expense of unsaturated C 18 FA suggests that fas alleles may reduce either 18:0-acyl carrier protein (AcP) desaturase or 18:1-ACP thioesterase activity. However, it also is conceivable that elevated 18:0 concentrations may result from increased 3-keto-acyl-ACP synthetase (KAS) II activity. To test the latter possibility, a population was created that segregated for the fas nc and the fap 2 alleles (the latter of which is associated with reduced KAS-II activity). Mendelian genetic analysis showed that these alleles represent independent genes at different gene loci and interact in an additive genetic manner to increase the total saturate concentration in this population. Based on this finding, we speculate that fas alleles probably encode 18:0-ACP desaturase or 18:1-ACP thioesterase in soybeans.The stearic acid (18:0) concentration in soybeans typically averages about 3% of crude oil (1). However, this phenotypic trait may be genetically altered by mutations at gene loci, designated Fas, which typically result in elevated 18:0 concentrations. Nearly all of these variants have been induced by chemical or X-ray mutagenesis, with the exception of a newly developed line, FAM94-41. FAM94-41 (9% 18:0) is the only known soybean germplasm that carries a serendipitous natural mutation, presumably at Fas, which now is temporarily designated as the recessive fas nc allele. Prior to the discovery of fas nc , five germplasm lines were reported to carry homozygous recessive alleles that influenced 18:0 concentrations in soybean oil: fas a [A6 (2)], fas b [FA41545 (3)], fas [A81-606085 (3)], st 1 [KK-2 (4)], and or st 2 [M25 (4)]. As reported (3), fas a (30% 18:0), fas b (15% 18:0), and fas (19% 18:0) are allelic to each other and presumably represent different mutations in the same gene. In an F 3 population segregating for st 1 and st 2 , the observation of progeny with 18:0 concentrations above and below the respective parental means provides evidence for two independently inherited genes governing higher 18:0 concentrations in soybeans. The proposed st 1 st 1 st 2 st 2 genotype may elevate the 18:0 concentration beyond 35% in crude oil (4). However, it is unknown whether st 1 or st 2 is allelic to fas a , fas b , ...

Mapping the Fas locus controlling stearic acid content in soybean

“…These stearic acid classes fit χ 2 goodness of fit criteria for 1:2:1 genotypic class ratios (table 1). This is consistent with the observation that an elevated stearic acid in FAM94-41 is governed by an alternative allele showing single gene inheritance (Pantalone et al 2002). Additive genetic effect P < 0.0001 P < 0.0001 P < 0.0001 Dominance genetic effect P < 0.05 NS P < 0.05 a.…”

“…A newly developed soybean line, FAM94-41, carrying a natural mutation, fasnc, has been recently described (Pantalone et al 2002). FAM94-41 is an agronomically robust high stearic acid line, which may become useful in reversing the apparent yield depression of material developed with other fas alleles.…”

Molecular mapping and identification of soybean fatty acid modifier quantitative trait loci

“…This modifier QTL may influence the major gene Fas, which governs 18:0 concentration and is in the same region. Spencer et al (26) detected Satt070 at 1.9 cM from the Fas locus having an r 2 of 67% in a population, which contained a natural mutation governing a two-fold increase in 18:0 (6,27). In our study the Essex allele of Satt070 had an additive effect of 4.5 g/kg.…”

Soybean Oil-Quality Variants Identified by Large-Scale Mutagenesis

“…Four mutants (lines [14][15][16][17] with reproducibly high levels of stearate ranging from 7 to 15% were identified in this study. Mutations in the SACPD-C gene are known to result in increased levels of stearic acid ranging from 9% to 30% [5,12,24]. There are thought to be at least two genetic loci that contribute to the high stearate phenotype [25].…”