Ligand-induced degradation of the ethylene receptor ETR2 through a proteasome-dependent pathway in Arabidopsis

Protein degradation plays an important role in modulating ethylene signal transduction in plants. Here we show that the ethylene receptor ETR2 is one such target for degradation and that its degradation is dependent upon perception of the signaling ligand ethylene. The ETR2 protein is initially induced by ethylene treatment, consistent with an increase in transcript levels. At ethylene concentrations above 1 mu l/liter, however, ETR2 protein levels subsequently decrease in a post-transcriptional fashion. Genetic and chemical approaches indicate that ethylene perception by the receptors initiates the reduction in ETR2 protein levels. The ethylene-induced decrease in ETR2 levels is not affected by cycloheximide, an inhibitor of protein biosynthesis, but is affected by proteasome inhibitors, indicating a role for the proteasome in ETR2 degradation. Ethylene-induced degradation still occurs in seedlings treated with brefeldin A, indicating that degradation of ETR2 does not require exit from its subcellular location at the endoplasmic reticulum. These data support a model in which ETR2 is degraded by a proteasome-dependent pathway in response to ethylene binding. Implications of this model for ethylene signaling are discussed.