Anacardic acids, a class of secondary compounds derived from fatty acids, are found in a variety of dicotyledonous families. Pest resistance (e.g., spider mites and aphids) in Pelargonium xhortorum (geranium) is associated with high levels (≈81%) of unsaturated 22:1ω5 and 24:1ω5 anacardic acids in the glandular trichome exudate. A single dominant locus controls the production of these ω5 anacardic acids, which arise from novel 16:1Δ11 and 18:1Δ13 fatty acids. We describe the isolation and characterization of a cDNA encoding a unique Δ9 14:0-acyl carrier protein fatty acid desaturase. Several lines of evidence indicated that expression of this desaturase leads to the production of the ω5 anacardic acids involved in pest resistance. First, its expression was found in pest-resistant, but not suspectible, plants and its expression followed the production of ω5 anacardic acids in segregating populations. Second, its expression and the occurrence of the novel 16:1Δ11 and 18:1Δ13 fatty acids and the ω5 anacardic acids were specific to tall glandular trichomes. Third, assays of the recombinant protein demonstrated that this desaturase produced the 14:1Δ9 fatty acid precursor to the novel 16:1Δ11 and 18:1Δ13 fatty acids. Based on our genetic and biochemical studies, we conclude that expression of this Δ914:0-ACP desaturase gene is required for the production of Δ5 anacardic acids that have been shown to be necessary for pest resistance in geranium.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Aug 6 1996|
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