Characterization of Newly Identified Natural High-Oleate Mutant from the USDA Cultivated Peanut Germplasm Collection

In plants and animals, natural genetic variation may exist in germplasm collection. Mining and utilizing this variation may provide benefits for new breed/cultivar development. From screening over 4,000 cultivated peanut germplasm accessions, we identified two natural mutant lines with 80% oleic acid by gas chromatography analysis. It is known that FAD2A and FAD2B are the two major genes involved in the conversion of oleic to linoleic acid in peanuts by fatty acid desaturase. Functional mutations in one or both genes can alter the oleate level.  By sequencing the coding region of these two genes, we identified a substitution of G448A in FAD2A and a substitution of C301G in FAD2B for both mutant lines. The substitution in FAD2A is the same as a previously identified one, resulting in a missense amino acid substitution of D150N; but the substitution in FAD2B is a new one, resulting in H101D. The new amino acid substitution on FAD2B is located in the first histidine box (one of the active sites) of the fatty acid desaturase and may significantly decrease its activity. Our mutants belong to subspecies hypogaea due to morphologically no flowers on the main stem, but F435, a previously identified natural high oleate mutant, is from subspecies fastigiata since it had flowers on the main stem. Therefore, we identified a class of natural mutants from the subspecies hypogaea and provided new additional genetic resources for breeders to use. Our results also demonstrate a good example of the importance and usefulness for preserving natural genetic diversity and utilizing germplasm collections.