Soybean oil has a wide variety of uses, and stearic acid, which is a relatively minor component of soybean oil is increasingly desired for both industrial and food applications. New soybean mutants containing high levels of the saturated fatty acid stearate in seeds were recently identified from a chemically mutagenized population. Six mutants ranged in stearate content from 6–14% stearic acid, which is 1.5 to 3 times the levels contained in wild-type seed of the Williams 82 cultivar. Candidate gene sequencing revealed that all of these lines carried amino acid substitutions in the gene encoding the delta-9-stearoyl-acyl-carrier protein desaturase enzyme (SACPD-C) required for the conversion of stearic acid to oleic acid. Five of these missense mutations were in highly conserved residues clustered around the predicted di-iron center of the SACPD-C enzyme. Co-segregation analysis demonstrated a positive association of the elevated stearate trait with the SACPD-C mutation for three populations. These missense mutations may provide additional alleles that may be used in the development of new soybean cultivars with increased levels of stearic acid.
To identify novel sources of genetic variation for the high oleic acid seed trait, soybean [Glycine max (L.) Merr] lines containing a higher fraction of oleic acid were identified through a forward‐genetic screen of a chemically mutagenized population. Mutant lines contained 30 to 40% of the total fatty acids as oleic acid. Nine of the lines identified contained novel point mutations in the FAD2–1A gene, which is known to be required for the conversion of oleic acid to linoleic acid. Mutation‐specific markers were developed to follow the mutant alleles in segregating populations and confirmed the genetic association of the novel polymorphisms with the elevated oleic acid trait. These lines can be used in breeding approaches and in combination with other genes to generate new soybean germplasm with high levels of oleic acid for the edible oil market.
Stearic acid is one of five major fatty acids found in soybean oil. It is a fully saturated lipid and is known for neutral or positive effects on LDL cholesterol when consumed by humans. Unfortunately, stearic acid only accounts for about 4% of the total seed oil produced in commodity soybean. Previous work has shown that stearic acid can reach levels as high as 28% of the total oil fraction when the SACPD‐C gene, encoding the delta‐9‐stearoyl‐acyl carrier protein desaturase responsible for most of the stearic acid variation in soybean seed, is ablated in combination with other loci. In order to increase stearic acid content and create soybeans with improved utility based on fatty acid composition, we combined mutations in SACPD‐C with other mutations in the fatty acid biosynthetic pathway. Soybean plants carrying mutant alleles of both SACPD‐C and FAD2‐1A produce seed with stearic acid levels from 14% to 21%, and with elevated levels of oleic acid. Soybeans carrying mutations in both SACPD‐C and FAD3A or FAD3C have both statistically significantly elevated levels of stearic acid (from 15–21%) and statistically reduced linolenic acid levels. Neither mutant combination appears to affect other agronomic properties such as plant morphology or seed protein levels making this a potentially viable trait.
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