JASMONATE IS ESSENTIAL FOR INSECT DEFENSE ARABIDOPSIS

The signaling pathways that allow plants to mount defenses against che wing insects are known to be complex, To investigate the role of jasmo nate in wound signaling in Arabidopsis and to test whether parallel or redundant pathways exist for insect defense, we have studied a mutant (fad3-2fad7-2fad8) that is deficient in the jasmonate precursor linol enic acid, Mutant plants contained negligible levels of jasmonate and showed extremely high mortality (approximate to 80%) from attack by la rvae of a common saprophagous fungal gnat, Bradysia impatiens (Diptera : Sciaridae), even though neighboring wild-type plants were largely un affected. Application of exogenous methyl jasmonate substantially prot ected the mutant plants and reduced mortality to approximate to 12%. T hese experiments precisely define the role of jasmonate as being essen tial for the induction of biologically effective defense in this plant -insect interaction. The transcripts of three wound-responsive genes w ere shown not to be induced by wounding of mutant plants but the same transcripts could be induced by application of methyl jasmonate, By co ntrast, measurements of transcript levels for a gene encoding glutathi one S-transferase demonstrated that wound induction of this gene is in dependent of jasmonate synthesis. These results indicate that the muta nt will be a good genetic model for testing the practical effectivenes s of candidate defense genes.