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Suppression of a P450 hydroxylase gene in plant trichome glands enhances natural-product-based aphid resistance

Abstract

Trichome glands on the surface of many higher plants produce and secrete exudates affecting insects, microbes, and herbivores. Metabolic engineering of gland exudation has potential for improving pest/disease resistance, and for facilitating molecular farming. We identified a cytochrome P450 hydroxylase gene specific to the trichome gland and used both antisense and sense co-suppression strategies to investigate its function. P450-suppressed transgenic tobacco plants showed a ≥41% decrease in the predominant exudate component, cembratriene-diol (CBT-diol), and a ≥19-fold increase in its precursor, cembratriene-ol (CBT-ol). Thus, the level of CBT-ol was raised from 0.2 to ≥4.3% of leaf dry weight. Exudate from antisense-expressing plants had higher aphidicidal activity, and transgenic plants with exudate containing high concentrations of CBT-ol showed greatly diminished aphid colonization responses. Our results demonstrate the feasibility of significantly modifying the natural-product chemical composition and aphid-interactive properties of gland exudates using metabolic engineering. The results also have implications for molecular farming.

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Acknowledgements

Special thanks go to D.M. Jackson for advice on aphid manipulations, P.L. Cornelius for assistance with statistical analysis, and G.M. Cheniae and K.F. Haynes for comments. We thank Charles Jones, Ryan Shepherd, and Lynn Zaleweski for assistance. The work was supported by grants from the Department of Energy Basic Energy Sciences (G.J.W.), Tobacco and Health Research Institute, University of Kentucky (Lexington, KY; G.J.W. and S.G.), and National Science Foundation/US Department of Agriculture–National Research Initiative, Interagency Metabolic Engineering 90.0 (G.J.W.).

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Correspondence to George J. Wagner.

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Figure 1: Pathway for the biosynthesis of cembranoids in nontransformed and antisense-expressing (1-31-2Q) plants.
Figure 2: Northern analysis of P450 gene expression in suppressed and control glands (A), and its reduced expression in antisense-expressing plant 1-31-2Q (B) and co-suppression plant FA4 (C).
Figure 3: Gas chromatographic profiles of trichome exudate compounds from nontransformed control (A) and 1-31-2Q (B) plants.
Figure 4: Survival of mature apterous aphids dosed with trichome exudates from control and 1-31-2Q leaves.
Figure 5: Colonization responses of aphids on control and high CBT-ol-producing 1-31-2Q and FA4 plants.