The effect of ethylene on MAPKinase-like activity in Arabidopsis thaliana

Protein kinase activity was studied in cytosolic extracts from leaves of wild type Ar Arabidopsis thaliana, the ethylene-insensitive mutant, Etr-1, and the constitutive triple-response mutant, ctr1. Treatment of mild type with ethylene resulted in increased myelin basic protein (MBP) phosphorylation, In etr1, constitutive protein kinase activity was lower than in wild type, but in ctr1, activity was enhanced. A protein of M-r similar to 47 kDa associated with MBP-phosphorylating activity was detected using in gel protein kinase assays and phosphorylation of this protein was promoted by ethylene treatment in mild type while activity in the mutants reflected that of MBP phosphorylation, Both MAPKinase (ERK 1) and phosphotyrosine antibodies immunoprecipitated MBP-phosphorylating activity and detected a polypeptide band at M-r similar to 47 kDa. Immunoprecipitated MBP-phosphorylating activity was again much lower in efr1 compared to wild type but much higher in ctr1. Antibodies to phosphorylated MAPKinase recognised proteins at similar to 47 kDa and the signal was upregulated in response to ethylene, The data obtained suggest that the detected protein(s) is a MAPKinase and provide further evidence confirming that a MAPKinase cascade(s) is involved in ethylene signal transduction, (C) 2000 Federation of European Biochemical Societies.