The wound-inducible expression of proteinase inhibitors (PIs) genes in tomato provides a powerful model system to elucidate the signal transduction pathway of sys- temic defense response. An increasing body of evidence indi- cates that systemin and jasmonic acid (JA) work in the same signaling pathway to activate the expression of PIs and other defense-related genes. However, little is known about how systemin and JA interact to regulate cell to cell communica- tion over long distances. Genetic analysis of the systemin/JA signaling pathway in tomato plants provides a unique op-portunity to dissect the mechanism by which peptide and oxylipin signals interact to coordinate systemic expression of defense-related genes. Previously, it has been proposed that systemin is the long-distance mobile signal for systemic ex-pression of defense related genes. However, recent genetic approach provided new evidence that jasmonic acid, rather than systemin, functions as the systemic wound signal, and that the peptide systemin works to regulate the biosynthesis of JA. The wound-inducible expression of proteinase inhibitors (PIs) genes in tomato provides a powerful model system to elucidate the signal transduction pathway of sys- temic defense response. An increasing body of evidence indi cates that system in and jasmonic acid (JA) work in the same signaling pathway to activate the expression of PIs and other defense-related genes. However, little is known about how system in and JA interact to regulate cell to cell communica tion over long distances. Genetic analysis of the systemin / JA signaling pathway in tomato plants provides a unique op-portunity to dissect the mechanism by which peptide and oxylipin signals interact to coordinate systemic expression of defense-related genes. Previously, it has been proposed that systemin is the long-distance mobile signal for systemic ex-pression of However, recent genetic approaches provided new evidence that jasmonic acid, rather than systemin, functions as the systemic wound signal, and that the peptide systemin works to regulate the biosynthesis of JA.