The high oleate trait in the cultivated peanut [Arachis hypogaea L.]. I. Isolation and characterization of two genes encoding microsomal oleoyl-PC desaturases

Plant oils rich in oleate are considered superior products compared to oils rich in polyunsaturated fatty acids. Peanut (Arachis hypogaea L.) is one o f the major oilseed crops, and high oleate mutant varieties with as much as 85% oleate have been reported. We examined the possibility that this mutan t phenotype resulted from reduction in the activity or the transcript level of microsomal oleoyl-PC desaturase. Two independently generated high oleat e mutants, M2-225 and 8-2122, and their partially isogenic lines with a nor mal oleate phenotype were used in this study. Two cDNA sequences coding for microsomal oleoyl-PC desaturases, ahFAD2A and ahFAD2B, have been isolated from the developing peanut seed with a normal oleate phenotype. Cultivated peanut is an allotetraploid, and sequence comparisons with the genes from t he putative diploid progenitor species suggested that ahFAD2A and ahFAD2B a re non-allelic, but homeologous genes originating from two different diploi d species. Northern analysis showed that the transcripts of oleoyl-PC desat urases are highly abundant in both normal and high oleate peanut seeds in t he second stage of development. Differential digestion of the RT-PCR produc ts revealed a restriction site polymorphism between ahFAD2A and ahFAD2B, an d allowed us to examine the level of transcript expressed from each gene. T he results indicate that ahFAD2A is expressed in both normal and high oleat e peanut seeds, but the steady state level of the ahFAD2B transcript is sev erely reduced in the high oleate peanut varieties. These data suggested tha t the reduction in ahFAD2B transcript level in the developing seeds is corr elated with the high oleate trait.