AN OCTADECANOID PATHWAY MUTANT (JL5) OF TOMATO IS COMPROMISED IN SIGNALING FOR DEFENSE AGAINST INSECT ATTACK

The activation of defense genes in tomato plants has been shown to be mediated by an octadecanoic acid-based signaling pathway in response t o herbivore attack or other mechanical wounding, We report here that a tomato mutant (JL5) deficient in the activation of wound-inducible de fense genes is also compromised in resistance toward the lepidopteran predator Manduca sexta (tobacco hornworm), Thus, we propose the name d efenseless1 (def1) for the mutation in the JL5 line that mediates this altered defense response. In experiments designed to define the norma l function of DEF1, we found that def1 plants are defective in defense gene signaling initiated by prosystemin overexpression in transgenic plants as well as by oligosaccharide (chitosan and polygalacturonide) and polypeptide (systemin) elicitors. Supplementation of plants throug h their cut stems with intermediates of the octadecanoid pathway indic ates that def1 plants are affected in octadecanoid metabolism between the synthesis of hydroperoxylinolenic acid and 12-oxo-phytodienoic aci d. Consistent with this defect, def1 plants are also compromised in th eir ability to accumulate jasmonic acid, the end product of the pathwa y, in response to wounding and the aforementioned elicitors. Taken tog ether, these results show that octadecanoid metabolism plays an essent ial role in the transduction of upstream wound signals to the activati on of antiherbivore plant defenses.