MOLECULAR GENETIC ANALYSIS OF THE HIGH OLEATE TRAIT IN PEANUT

¹ Dept. of Biological Sciences, Clemson University, Clemson, SC 29634-1903

² AgraTech Seeds Inc., P.O. Box 644, Ashburn, Georgia 31714

Plant oils rich in oleate are considered superior products compared to oils rich in polyunsaturated fatty acids. High oleate peanut varieties with 80% oleate have been reported. This high oleate trait is recessive, and it exhibits one- or two- gene-segregation depending on the normal oleate varieties in crosses. The objective of this study was to understand the molecular nature of the high oleate trait. Two microsomal oleoyl-PC desaturase genes (ahFAD2A and ahFAD2B) that are the primary candidates for controlling oleate content in seeds, were isolated from the cultivated peanut. Cultivated peanut is an allotetraploid, and sequence comparisons with the genes from the putative diploid progenitor species suggested that ahFAD2A and ahFAD2B are non-allelic, but homeologous genes originating from two different diploid species. We examined the potential role of these two genes in the high oleate phenotype by analyzing peanut seeds for transcripts of each, comparing their nucleotide sequences in high and normal oleate varieties, and testing the enzyme activity of each in yeast. The data suggest that mutations in ahFAD2A and a significantly reduced transcript level of ahFAD2B are directly correlated with the high oleate. It appears that some peanut breeding lines have a mutant ahFAD2A allele, and depending on the allelic constitution at both loci of the normal oleate peanuts in a cross, a one or two-gene segregation pattern is displayed. These molecular data support two-recessive-gene model for the high oleate trait in peanut, and clarify the segregation patterns of the trait in breeding crosses.