Poster: Late and Moved Abstracts

Abs # 944: SCF^EBF1/EBF2-mediated degradation of EIN3 and EIL1 transcription factors in Arabidopsis ethylene responses

Presenter:	Guo, Hongwei , guo@salk.edu
Authors	Guo, Hongwei  (A)   Ecker, Joseph R (A)
Affiliations:	(A): the Salk Institute for Biological Studies

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. We found 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. ein3 mutation could partially suppress the defects caused by loss of function of EBF1 and 2, whereas ein2 mutation could not. Plants overexpressing either F-box gene display ethylene insensitivity and destabilization of EIN3 protein. In addition, we found that EIN3 homolog, EIL1, also undergoes a SCF^EBF1/2-mediated protein degradation that is antagonized by ethylene. These results reveal that a ubiquitin/proteasome pathway negatively regulates ethylene responses by targeting EIN3 and EIL1 for degradation, and highlight the regulation of EIN3/EIL transcription factors as the key step in the response to ethylene.