Activation of tomato PR and wound-related genes by a mutagenized tomato MAP kinase kinase through divergent pathways

A mitogen-activated protein kinase kinase (MAPKK) gene, tMEK2, was isolated from tomato cv. Bonny Best. By mutagenesis, a permanently active variant, tMEK2(MUT), was created. Both wild-type tMEK2 and mutant tMEK2(MUT) were driven by a newly described strong plant constitutive promoter, tCUP, in a tomato protoplast transient gene expression system. Pathogenesis-related genes, PR1b1, PR3 and Twi1, and a wound-inducible gene, ER5, were activated by tMEK2(MUT). Specific inhibitors of p38 class MAPK inhibited tMEK2(MUT)-induced activation of PR3 and ER5 genes but not that of the PR1b1 or Twi1 gene. Arabidopsis dual-specificity protein tyrosine phosphatase1 (DsPTP1) and maize protein phosphatase 1 (PP1) inhibited tMEK2(MUT)-induced activation of the ER5 gene and the Twi1 gene, respectively, whereas PR1b1 and PR3 were not affected by either AtDsPTP1, or maize PP1, or Arabidopsis protein phosphatase 2A (PP2A). We have demonstrated for the first time that a single MAPKK activates an array of PR and wound-related genes. Our observation indicates that the activation of the genes downstream of tMEK2 occurs through divergent pathways and that tMEK2 may play an important role in the interaction of signal transduction pathways that mediate responses to both biotic (e.g. disease) and abiotic stresses (e.g. wound responsiveness).