[Show abstract][Hide abstract] ABSTRACT: Mitogen-activated kinase (MAPK) cascades are universal signal transduction pathways in eukaryotic cells. In tobacco, two MAPKs, wound-induced protein kinase (WIPK) and salicylic acid (SA)-induced protein kinase (SIPK) are activated by biotic and abiotic stresses. Both WIPK and SIPK positively regulate the biosynthesis of jasmonic acid (JA) and/or ethylene (ET), while negatively regulate SA accumulation. We showed previously that recombinant tobacco MAPK phosphatase (NtMKP1) protein dephosphorylates and inactivates SIPK in vitro, and over-expression of NtMKP1 repressed wound-induced activation of both SIPK and WIPK. To elucidate the role of NtMKP1 in response to biotic and abiotic stresses, we generated transgenic tobacco plants in which NtMKP1 expression was suppressed. Suppression of NtMKP1 expression resulted in enhanced activation of WIPK and SIPK and production of both JA and ET upon wounding. Wound-induced expression of JA/ET inducible genes, basic PR-1 and PI-II, was also significantly enhanced in these plants. Furthermore, NtMKP1-suppressed plants exhibited enhanced resistance against a necrotrophic pathogen, Botrytis cinerea, and lepidopteran herbivores, Mamestra brassicae and Spodoptera litura. These results suggest that NtMKP1 negatively regulates wound response and resistance against both necrotrophic pathogens and herbivorous insects through suppression of JA/ET pathways via inactivation of MAPKs.