A novel allele of GmSACPD-C associated with high seed stearic acid concentration in an EMS-induced mutant PE980 in soybean

Stearic acid is a relatively minor component of soybean [Glycine max (L.) Merr.] seed oil. Increasing the stearic acid concentration is desired for industrial and food applications, as well as enhanced oxidative stability of the oil. Several ethyl methane sulfonate (EMS)-induced mutants with elevated seed stearic acid concentration have been reported in soybean. Such mutants were often found to carry alterations in the GmSACPD-C gene encoding Δ9-stearoylacyl carrier protein-desaturase, the enzyme that catalyzes the conversion of stearic acid to oleic acid in the fatty acid biosynthetic pathway. In the present study, we identified a new GmSACPD-C allele in an EMS-induced highstearic- acid mutant PE980. The mutant showed a seed stearic acid concentration of ~160 g kg^-1, fourfold that of the wild-type ‘Pungsannamul’. A single base substitution from guanine to adenine at genomic position 703 of first exon of the GmSACPD-C gene was identified through sequencing, and validated by cosegregation analysis of 167 F₂ plants using an allele-specific SimpleProbe marker. The mutation caused a valine to methionine (+70 position) change in the predicted GmSACPD-Cprotein sequence. The sequence alignments and three-dimensional structure modeling of GmSACPD-C showed that the V70M mutation affects substrate binding and dimerization to reduce enzyme activity. Since the mutant showed significant reductions in seed yield compared with the wild type, marker-assisted backcrossing may be needed to reduce the yield gap.