Ethylene Responses Are Negatively Regulated by a Receptor Gene Family in Arabidopsis thaliana

A family of genes including ETR1, ETR2, EIN4, ERS1, and ERS2 is implicated in ethylene perception in Arabidopsis thaliana. As only dominant mutations were previously available for these genes, it was unclear whether all of them are components in the ethylene signaling pathway and whether they code for positive or negative regulators of ethylene responses. In this study, we have isolated loss-of-function mutations of four of these genes (ETR1, ETR2, EIN4, and ERS2) and identified an ethylene-independent role of ETR1 in promoting cell elongation. Quadruple mutants had constitutive ethylene responses, revealing that these proteins negatively regulate ethylene responses and that the induction of ethylene response in Arabidopsis is through inactivation rather than activation of these proteins.