The octadecanoid signaling pathway has been shown to play an important role in plant defense against various chewing insects and some pathogenic fungi. Here, we examined the interaction of a cell-content feeding arachnid herbivore, the two-spotted spider mite (Tetranychus urticae Koch), with cultivated tomato (Lycopersicon esculentum) and an isogenic mutant line (defenseless-1 [def-1]) that is deficient in the biosynthesis of the octadecanoid pathway-derived signal, jasmonic acid (JA). Spider mite feeding and fecundity on def-1 plants was significantly greater than on wild-type plants. Decreased resistance of def-1 plants was correlated with reduced JA accumulation and expression of defensive proteinase inhibitor (PI) genes, which were induced in mite-damaged wild-type leaves. Treatment of def-1 plants with methyl-JA restored resistance to spider mite feeding and reduced the fecundity of female mites. Plants expressing a 35S::prosystemin transgene that constitutively activates the octadecanoid pathway in a Def-1-dependent manner were highly resistant to attack by spider mites and western flower thrips (Frankliniella occidentalis), another cell-content feeder of economic importance. These findings indicate that activation of the octadecanoid signaling pathway promotes resistance of tomato to a broad spectrum of herbivores. The techniques of amplified fragment length polymorphism (AFLP) and bulk segregant analysis were used to map the Def-1 gene to a region on the long arm of chromosome 3 that is genetically separable from the map position of known JA biosynthetic genes. Tight linkage of Def-1 to a T-DNA insertion harboring the maize (Zea mays) Dissociation transposable element suggests a strategy for directed transposon tagging of the gene.Plant resistance to arthropod herbivores is often mediated by phytochemicals that negatively affect the feeding, growth, or reproduction of the attacking pest (Karban and Baldwin, 1997; Walling, 2000). Although many defensive compounds have been identified from diverse plant species, relatively little is known about the underlying genetic mechanisms that control their biosynthesis in response to developmental and environmental cues. Lycopersicon spp. provide an attractive model system to address this question. Cultivated tomato (Lycopersicon esculentum) is a natural host to over 100 arthropod herbivores that feed on roots, leaves, or fruit (Lange and Bronson, 1981). Included among the major pests of tomato are adult and larval stages of Coleoptera (beetles), Lepidoptera (moths), Diptera (flies), Thysanoptera (thrips), Heteroptera (true bugs), Homoptera (aphids and whiteflies), and Acari (spider mites).Natural resistance of tomato to many herbivores is attributed to both constitutive and inducible defensive phytochemicals (Farrar and Kennedy, 1992). Among the most thoroughly studied inducible defenses in tomato are proteinase inhibitor (PI) proteins that inhibit digestive enzymes in the gut of some insect herbivores (Green and Ryan, 1972; Broadway and Duffey, 1986). Wound-induc...

Allene oxide synthase (AOS) and fatty acid hydroperoxide lyase (HPL) are plant-specific cytochrome P450s that commit fatty acid hydroperoxides to different branches of oxylipin metabolism. Here we report the cloning and characterization of AOS (LeAOS) and HPL (LeHPL) cDNAs from tomato (Lycopersicon esculentum). Functional expression of the cDNAs inEscherichia coli showed that LeAOS andLeHPL encode enzymes that metabolize 13- but not 9-hydroperoxide derivatives of C18 fatty acids. LeAOS was active against both 13S-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic acid (13-HPOT) and 13S-hydroperoxy-9(Z),11(E)-octadecadienoic acid, whereas LeHPL showed a strong preference for 13-HPOT. These results suggest a role for LeAOS andLeHPL in the metabolism of 13-HPOT to jasmonic acid and hexenal/traumatin, respectively. LeAOS expression was detected in all organs of the plant. In contrast, LeHPLexpression was predominant in leaves and flowers. Damage inflicted to leaves by chewing insect larvae led to an increase in the local and systemic expression of both genes, with LeAOS showing the strongest induction. Wound-induced expression ofLeAOS also occurred in the def-1 mutant that is deficient in octadecanoid-based signaling of defensive proteinase inhibitor genes. These results demonstrate that tomato uses genetically distinct signaling pathways for the regulation of different classes of wound responsive genes.