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GENOMICS, MOLECULAR GENETICS & BIOTECHNOLOGY

A Mutation in a 3-Keto-Acyl-ACP Synthase II Gene is Associated with Elevated Palmitic Acid Levels in Soybean Seeds

^a Crop Science Dep., North Carolina State Univ., Raleigh, NC 27695
^b USDA-ARS, North Carolina State Univ., Raleigh, NC 27695
^c USDA-ARS, Oilseeds and Bioscience Program, Beltsville, MD 20705. K. Aghoram, current address: Dep. of Biology and Health Science, Meredith College, Raleigh, NC 27607

^* Corresponding author (ralph_dewey{at}ncsu.edu)

Palmitic acid is the major saturated fatty acid component of soybean [Glycine max (L.) Merr.] oil, typically accounting for approximately 11% of total seed oil content. Several genetic loci have been shown to control the seed palmitate content of soybean. One such locus, fap₂, mediates an elevated seed palmitate phenotype. Previous biochemical studies indicated that the fap₂ locus is associated with a reduction in the activity of 3-keto-acyl-ACP synthase II (KAS II), an enzyme that initiates the elongation of palmitoyl-ACP to stearoyl-ACP in the plastid. The objective of the present research was to define the molecular basis by which the fap₂ locus increases seed palmitate levels. We isolated two closely related, yet unique KAS II cDNAs, designated GmKAS IIA and GmKAS IIB, from soybean cultivar Century (Fap₂, Fap₂) and its derivative high palmitate germplasm C1727 (fap₂, fap₂). The GmKAS IIB cDNAs recovered from Century and C1727 were identical. In contrast, a single base-pair substitution was found in the GmKAS IIA gene from C1727 versus Century which converted a tryptophan codon into a premature stop codon, a mutation that would be predicted to render the encoded enzyme nonfunctional. Knowledge of the DNA sequence polymorphism led to the development a facile, robust cleavage amplified polymorphic sequence (CAPS) marker that readily distinguishes the mutant GmKAS IIA gene. This marker faithfully associated with a second independent germplasm line bearing the fap₂ locus, and thus may be useful in breeding programs that target the development of high palmitate soybean cultivars.

Abbreviations: ACP, acyl carrier protein • CAPS, cleaved amplified polymorphic sequence • EMS, ethyl methane sulfonate • ESTs, expressed sequence tags • FAT, fatty acid thioesterase • KAS, 3-keto-acyl-ACP synthase

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