Alteration of the omega-3 fatty acid desaturase gene is associated with reduced linolenic acid in the A5 soybean genotype

Reducing the linolenic acid (18:3(omega 3,6,9)) concentration of soybean [Glycine max (L.) Merr.] oil may lessen the need for chemical hydrogenation and enhance flavor stability. Soybean genotypes A5 and A23 have reduced linolenic acid concentration compared with current cultivars. Seed linolenic acid is synthesized primarily by the omega-3 fatty acid desaturase located in the microsomes. The objective of this research was to study whether this enzyme has a role in reducing the fatty acid levels in the soybean genotypes A5 and A23. DNA from A5 and A23 was analyzed by gel-blot hybridization with a cDNA encoding the omega-3 fatty acid desaturase. A5 and lines selected from it have a DNA fragment missing compared to A23 and lines with normal linolenic acid concentration. Seventy F-4:5 lines from a population segregating for linolenic acid concentration were scored for presence or absence of the fragment. The absence of the fragment was significantly (P less than or equal to 0.0001) associated with a reduced linolenic acid level and accounted for 67% of the variation for linolenic acid in the population. These results suggest that the reduced linolenic acid concentration in A5 was at least partially the result of a full or partial deletion of a microsomal omega-3 desaturase gene. No DNA polymorphisms were found for the desaturase gene in A23, so no mutations could be studied in this line.