| In 2003, soybeans represented 56% of the world oilseed production, and 34% of the soybeans were produced in the United States. Soybean oil contains 7--9% of linolenic acid, that makes the oil very susceptible to oxidation upon storage and heating. In order to reduce the linolenic acid content in the oil, the industry uses hydrogenation, but this reduction leads to the formation of trans fatty acids that have been linked to increased risks of heart diseases. One of the goals in soybean breeding programs is the reduction of the linolenic acid content in the seeds to make the oil suitable for storage and heating without hydrogenation. The objective of this study was to develop molecular markers to help selecting for low linolenic lines in the breeding program at South Dakota State University. We first determined the number of genes of key enzymes responsible for the linolenic acid content in soybean seeds. We found that the biotin carboxyl carrier protein subunit of acetyl-CoA carboxylase (ACCase) has four genes instead of the two previously described. Four genes also control the o-6 fatty acid desaturase. We confirmed that the o-3 fatty acid desaturase is controlled by three genes and found a fourth pseudogene. We characterized the three genes that directly control linolenic acid content in the oil, FAD3A, FAD3B and FAD3C. Those three genes have 8 exons and 7 introns. When the exons were fairly conserved between the three genes, the intron sequences were very dissimilar. Finally, we developed a molecular marker associated with the low linolenic acid trait that allowed the direct selection for this trait among the lines developed in the breeding program. |
