Metabolic mechanisms associated with alleles governing the 16:0 concentration of soybean oil

• Published in: Journal of the American Oil Chemists' Society 2001-04, Vol.78 (4), p.335-340
• Main Authors: Wilson, R. F., Marquardt, T. C., Novitzky, W. P., Burton, J. W., Wilcox, J. R., Kinney, A. J., Dewey, R. E.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Developing‐seed; Enzymes; fap‐alleles; Fat industries; Fatty acids; Food industries; Fundamental and applied biological sciences. Psychology; genetics; Genetics and breeding of economic plants; glycerolipid composition; Glycine max; Metabolism; oil; palmitic acid; phospholipid; Phospholipids; saturated fat; Varietal selection. Specialized plant breeding, plant breeding aims; Yield, quality, earliness, varia
• ISSN: 0003-021X; 1558-9331
• DOI: 10.1007/s11746-001-0265-4

Soybean [Glycine max (L.) Merr.] oil typically contains ca. 11% palmitic acid, but germplasm has been developed with less than 4% to about 35% 16∶0, A number of recessive alleles associated with these phenotypes have been described thattrepresent different mutations at Fap loci, however, the gene products (enzymes) produced by these alleles are unknown. This work attempts to define the metabolic activities that are regulated by the fap1, fap2, and fapnc alleles in soybean. Observation of de novo synthesis and metabolic turnover of fatty acids esterified to phospholipids in cotyledons during the period of peak oil accumulation revealed genotypic differences in the supply of 16∶0‐CoA from plastids. These metabolic studies narrowed the identification of fap1, fap2, and fapnc alleles to the genes that encode or regulate the 3‐keto‐acyl‐ACP synthetase II (where ACP is acyl carrier protein), 16∶0‐ACP thioesterase, 18∶0‐ACP desaturase, or 18∶1‐ACP thioesterase enzymes. Kinetic analyses suggested that the fap2 mutation results in a decreased 3‐keto‐acyl‐ACP synthetase II activity. Deficiencies in 16∶0‐ACP thioesterase activity represented the most likely explanation of fap1 and fapnc gene function. This hypothesis was strongly supported by Northern blot assays that revealed a significant reduction in the accumulation of transcripts corresponding to the 16∶0‐ACP thioesterase in germplasm homozygous for the fapnc allele.