Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 14, 2010
Publication Date: April 1, 2010
Citation: Upchurch, R.G. and Ramirez, M.E. 2010. Gene expression profiles of soybeans with mid-oleic acid seed phenotype. J. of the Am. Oil Chem. Soc. 87:857-864.
Interpretive Summary: It is known that seeds of the soybean mutant line M23 yield oil higher in oleic acid (50-60%, “mid-oleic”), a type of oil desired by food and chemical industries. M23 is mid-oleic because it lacks a particular fatty acid biosynthesis gene FAD2-1A. Agronomically improved M23-derived soybean lines that have the mid-oleic trait have been developed through plant breeding, but sometimes these shown trait instability in the field. Since other natural sources, though less well characterized, of the mid-oleic trait are available, these sources need to be analyzed. We analyzed the expression of eight genes associated with oleic acid biosynthesis in five natural mid-oleic soybean lines by comparing their gene expression to that of mutant M23 and the conventional cultivar Dare. We found that higher expression of three and lower expression of four of the genes was associated with the mid-oleic trait in the natural soybean lines. This finding suggests that multiple genes contribute to the expression of the mid-oleic trait and some of these genes must regulate the expression of the oleic acid biosynthesis genes.
Seeds of the mid-oleic acid soybean mutant M23 accumulate higher levels of oleic acid (50-60% oleate) by virtue of a deletion of GmFAD2-1A, an isoform of the microsomal omega-6 oleate desaturase gene. In other less well characterized natural soybean varieties that are phenotypically mid-oleic, little is known about the expression levels of omega-6 desaturase GmFAD2 genes and other candidate genes that may account for the elevated oleic acid content in their seed. We compared the steady-state transcript abundance during seed development of omega-6 fatty acid desaturase, delta-9 stearoyl acyl carrier protein desaturase (GmSACPD), and the oleate-ACP thioesterase (GmFATB) isoforms/genes in five natural mid-oleic varieties and mutant M23 to gene expression data for conventional cultivar Dare. We found that up-regulated expression of the three GmSACPD isoforms, particularly GmSACPD-C as well as down-regulated expression of GmFAD2-1A, Gm FAD2-1B, GmFAD2-2, and GmFAD2-3 could, in many instances, be associated with the mid-oleic phenotype of M23 and the natural variants. This finding suggests that, of the multiple soybean genomic regions (QTLs) either confirmed or suspected of involvement in the mid-oleic fatty acid phenotype, some must contain genes that direct and regulate gene transcription.