Genetic Analysis of Wound Signaling in Tomato. Evidence for a Dual Role of Jasmonic Acid in Defense and Female Fertility

Genetic analysis of the wound response pathway in tomato (Lycopersicon esculentum) indicates that prosystemin and systemin are upstream components of a defensive signaling cascade that involves complex regulation of jasmonic acid (JA) biosynthesis and the ability of cells to perceive and respond to JA. Recent identification of JA response mutants provides evidence for the hypothesis that the JA transduction pathway also plays an important role in female reproductive development. Many plants respond to insect attack and wounding by synthesizing an array of phytochemicals that decrease the ability of herbivores to colonize, feed, or reproduce on the plant (Green and Ryan, 1972; Karban and Baldwin, 1997). Wound-inducible proteinase inhibitors (PIs) provide an attractive model system in which to study the signal transduction pathways that regulate this form of defense. In tomato, damage to a single leaflet by mechanical wounding or herbivory results in localized and systemic expression of two Ser PI-encoding genes (Inh-Iand Inh-II) within about 2 h (Ryan, 2000; Howe et al., 2000). These proteins can accumulate to high levels in leaves of the damaged plant, where they play a defensive role by inhibiting digestive proteases of some lepidopteran insects. In their pioneering study of wound-inducible PIs 30 years ago, Green and Ryan (1972) proposed that chemical signals generated at the site of wounding traverse the vascular system to activate the systemic expression of PIs. Although many of the signals involved in this response have been identified, relatively little is known about the mechanisms by which they are produced and transported between cells.