Submitted to: The Plant Genome
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/15/2006
Publication Date: 12/1/2006
Citation: Schlueter, J.A., Sanders, I.F., Deshpande, S., Yi, J., Seigfried, M., Roe, B.A., Schlueter, S.D., Scheffler, B.E., Shoemaker, R.C. 2006. The fad2 gene family of soybean:insights into the structural and functional divergence of a paleopolyploid genome. The Plant Genome. 1:14-26. Interpretive Summary: In soybean, undesirable types of fatty acids are produced that decrease shelf life of the edible oil. Two genes affecting this production were previously studied. It is known that production of these undesirable fatty acids is controlled by additional genes and affected by temperature. A better understanding of this family of genes may aid in helping breeders and biochemists improve soybean oil quality. In this study the authors identified five of the genes within this family. They found that two of the genes are in parts of separate chromosomes that are closely related and that contain many of the same genes. Three of the other genes, although related to each other, were on different chromosomes and were in regions that seemed to have nothing in common. The authors also identified one of the genes as producing more product at cool temperatures. Thus, this gene may be important in determining the levels of undesirable fatty acids. This information is important to biochemists who are trying to understand the controlling factors of soybean oil quality, and to biologists who are studying the evolution of the hereditary material of important crops such as soybean.
Technical Abstract: The omega-6 fatty acid desaturase (FAD2) gene family in soybean consists of at least five members in four regions of the genome. These desaturases are responsible for the conversion of oleic acid to linoleic acid. Bacterial artificial chromosomes (BACs) corresponding to these loci were sequenced to investigate both structural and functional conservation between duplicate loci. Sequence comparisons between the regions showed that the soybean genome is a mosaic with some regions retaining high sequence conservation in both the genic and intergenic regions while others have only the FAD2 genes in common. Genetic mapping using SSRs identified within these sequences showed that two BACs with high sequence identity mapped to linkage groups I and O; linkage groups that have other syntenic markers between them. Another BAC mapped to linkage group L. The last BAC contained significant repetitive sequence and was unable to be mapped by SSRs. Reverse transcriptase-PCR analysis of the five FAD2 genes showed that the newly identified FAD2-2B and FAD2-2C copies are the best candidates for temperature dependent expression changes in developing pod tissue. Semi-quantitative RT-PCR confirmed these results with FAD2-2C showing upwards of an eight-fold increase in expression in developing pods grown in cooler conditions relative to those grown in warm conditions. The implications of these results suggest a candidate gene for decreasing the levels of linoleic acid in developing pods grown in cooler climates.