OVEREXPRESSION OF THE FAD3 DESATURASE GENE IN A MUTANT OF ARABIDOPSIS

mutant of Arabidopsis contained increased levels of 18:3 fatty acids a nd correspondingly decreased levels of 18:2. The fatty acid phenotype was strongly expressed in root and seed tissues and this observation, together with other data, suggested that the mutation leads to increas ed activity of the endoplasmic reticulum 18:2 desaturase encoded by th e FAD3 gene. Gel-blot analysis of RNA from wild-type and mutant plants established that FAD3 transcript levels were increased 80% in the mut ant relative to the wild type. Genetic analysis demonstrated a linkage between the new mutation and the fad3 locus. Linkage of the mutation to fad3 raises the possibility that the lesion is an alteration to the promoter or another regulatory region of the FAD3 gene, which results in increased transcription.