Epidermis-specific metabolic engineering of sesquiterpene formation in tomato affects the performance of potato aphid (Macrosiphum euphorbiae)

Tomato species produce terpenes in their glandular trichomes contributing to host-plant resistance. We have identified sesquiterpenes in accessions of the wild tomato Solanum habrochaites that negatively affect performance and choice behavior of potato aphid (Macrosiphum euphorbiae). Since cultivated tomato (Solanum lycopersicum) primarily accumulates monoterpenes, introduction of these sesquiterpene traits is a promising approach to improve resistance. Introgression of S. habrochaites terpene biosynthetic genes into S. lycopersicum resulted in the formation of respective sesquiterpenes in glandular trichomes, however, at significantly lower levels than in the wild parent. Aphids use their mouthpart to penetrate and probe plant tissues to ultimately access vascular tissue and ingest phloem sap. While glandular trichome derived terpenes affect initial steps of aphid feeding, introducing sesquiterpenes into additional tissues via metabolic engineering could further reduce aphid tissue penetration. Two multicistronic expression constructs were developed based on the identified S. habrochaites sesquiterpene traits. Both constructs are composed of sequences encoding a prenyltransferase, terpene synthase, and enhanced-green-fluorescent-protein. All coding sequences were linked by nucleotide sequences encoding the foot-and-mouth disease virus 2A self-processing oligopeptide which allows their co-expression under one promoter. Expression of both constructs under the epidermis-specific Arabidopsis CER5-promoter in tomato leaves resulted in formation of two sets of defensive sesquiterpenes, β-caryophyllene/α-humulene and (−)-endo-α-bergamotene/(+)-α-santalene/(+)-endo-β-bergamotene, respectively. The epidermis-specific transgene expression and terpene formation were verified by fluorescence microscopy and tissue fractionation. In addition, longevity and fecundity of M. euphorbiae feeding on these engineered tomato leaves were reduced, demonstrating the efficacy of this novel aphid control strategy.