EXPRESSION OF A DELTA(9) 14 0-ACYL CARRIER PROTEIN FATTY-ACID DESATURASE GENE IS NECESSARY FOR THE PRODUCTION OF OMEGA(5) ANACARDIC ACIDS FOUND IN PEST-RESISTANT GERANIUM (PELARGONIUM-XHORTORUM)/

Anacardic acids, a class of secondary compounds derived from fatty aci ds, are found in a variety of dicotyledonous families. Pest resistance (e.g., spider mites and aphids) in Pelargonium xhortorum (geranium) i s associated with high levels (approximate to 81%) of unsaturated 22:1 omega(5) and 24:1 omega(5) anacardic acids in the glandular trichome exudate, A single dominant locus controls the production of these omeg a(5) anacardic acids, which arise from novel 16:1 Delta(11) and 18:1 D elta(13) fatty acids, We describe the isolation and characterization o f a cDNA encoding a unique Delta(9) 14:0-acyl carrier protein fatty ac id desaturase. Several lines of evidence indicated that expression of this desaturase leads to the production of the omega(5) anacardic acid s involved in pest resistance. First, its expression was found in pest -resistant, but not suspectible, plants and its expression followed th e production of omega(5) anacardic acids in segregating populations, S econd, its expression and the occurrence of the novel 16:1 Delta(11) a nd 18:1 Delta(13) fatty acids and the omega(5) anacardic acids were sp ecific to tall glandular trichomes. Third, assays of the recombinant p rotein demonstrated that this desaturase produced the 14:1 Delta(9) fa tty acid precursor to the novel 16:1 Delta(11) and 18:1 Delta(13) fatt y acids. Based on our genetic and biochemical studies, we conclude tha t expression of this Delta(9) 14:0-ACP desaturase gene is required for the production of omega(5) anacardic acids that have been shown to be necessary for pest resistance in geranium.