The naturally occurring high oleate oil character in some peanut varietiesresults from reduced oleoyl-PC desaturase activity from mutation of aspartate 150 to asparagine

Commercially important high oleate seed oils, meaning that they are low in polyunsaturated fatty acid content, are resistant to developing rancidity A peanut cultivar (Arachis hypogaea L,.) derived from a naturally occurring peanut has low oleoyl-PC desaturase activity, the key enzyme in the product ion of linoleate, normally an abundant polyunsaturated fatty acid. Two gene s for this enzyme are expressed in peanut seeds, and when they were separat ely expressed in yeast (Saccharomyces cerevisiae), one produced less linole ate than the of her. Although the two cDNA encode similar sequence proteins , they differ by four amino acids. Aspartate at position 150 was asparagine in the low activity copy. An asparate was present in many membrane desatur ases and other related membrane enzymes at an equivalent location suggestin g that the mutation at 150 was key to the low activity. In this work, site- specific mutagenesis was used to change the aspartate in the high activity enzyme to asparagine and to change asparagine in the lower activity enzyme to aspartate. These changes, upon expression in yeast, resulted in nearly c omplete loss of activity of the previously more active desaturase and resto red activity to the previously less active desaturase. This decrease in act ivity of the one gene, a consequence of mutation from aspartate 150 to aspa ragine, together with reduction in transcript level of the high activity ge ne in the mutant variety, suggest that these alterations are the molecular basis of the high oleate phenotype in some commercial varieties of peanut.