Plant Responses to Ethylene Gas Are Mediated by SCFEBF1/EBF2-Dependent Proteolysis of EIN3 Transcription Factor

Plants use ethylene gas as a signal to regulate myriad developmental processes and stress responses. The Arabidopsis EIN3 protein is a key transcription factor mediating ethylene-regulated gene expression and morphological responses. Here, we report that EIN3 protein levels rapidly increase in response to ethylene and this response requires several ethylene-signaling pathway components including the ethylene receptors (ETR1 and EIN4), CTR1, EIN2, EIN5, and EIN6. In the absence of ethylene, EIN3 is quickly degraded through a ubiquitin/proteasome pathway mediated by two F box proteins, EBF1 and EBF2. Plants containing mutations in either gene show enhanced ethylene response by stabilizing EIN3, whereas efb1 efb2 double mutants show constitutive ethylene phenotypes. Plants overexpressing either F box gene display ethylene insensitivity and destabilization of EIN3 protein. These results reveal that a ubiquitin/proteasome pathway negatively regulates ethylene responses by targeting EIN3 for degradation, and pinpoint EIN3 regulation as the key step in the response to ethylene.