Characterization of the Ethylene Receptor/CTR1 Signaling Complex of Arabidopsis

The plant hormone ethylene is perceived by a five-member family of receptors in Arabidopsis. The ethylene receptors function in conjunction with the Raf-like kinase CTR1 to negatively regulate ethylene signaling. We performed a co-IP analysis to examine the interaction of CTR1 with members of the ethylene receptor family. Our results demonstrate an interaction of CTR1 with the ethylene receptors ETR1, ETR2 and EIN4, but not with the ethylene receptors ERS1 and ERS2, suggesting that the receiver domains of the receptors help stabilize the interaction. We also examined the effect of ethylene on protein levels of the ethylene receptors and CTR1. We observed an increase in protein levels of ERS1, ERS1, ETR2, EIN4, and CTR1 in response to 1 µL/L ethylene, but a decrease in protein levels at higher concentrations of ethylene, consistent with ligand-mediated post-translational degradation. ETR1 was not sensitive to ethylene-induced degradation in wild-type seedlings, but was sensitive when in a null ctr1 mutant background, suggesting that the ETR1-CTR1 interaction serves to protect ETR1 from ligand-mediated degradation. Our results point to dynamic post-translational changes in the ethylene-receptor signaling complex, which are predicted to regulate the sensitivity of plants to ethylene.