ABSTRACT
As an example, genomic and plant breeding research has successfully exploited natural mutations in the FAD genes. Agronomic soybean varieties (Table 2) such as Soyola have a natural mutation in FAD3, which results in lower linolenic acid (3). Germplasm, such as N85-2176, exhibited the first combination of natural mutations in both FAD2 and FAD3 genes (4). In that case, the oil phenotype had low linolenic acid plus elevated oleic acid. Then, there is the first known mid-oleic soybean germplasm, N98-4445, which has another natural mutation that further reduces n-6 desaturase or FAD2 activity (5). Investigations into the nature of these mutations have led to the discovery that the soybean has two distinct isoforms of the FAD2 gene, α and β. This may be attributed to the fact that the soybean is an ancient autotetraploid, which means that there is a duplicate set of complementary chromosomes in the soybean genome. N98-4445 has only one set of these FAD2 genes, the α-isoform. Thus, we conclude that the biological basis for the mid-oleic trait in N98-4445 is a natural gene deletion event in which the β-isoform of FAD2-1 was lost.
