Nuclear events in ethylene signaling: a transcriptional cascade mediated by ETHYLENE-INSENSITIVE3 and ETHYLENE-RESPONSE-FACTOR1

Response to the gaseous plant hormone ethylene in Arabidopsis requires the EIN3/EIL family of nuclear proteins. The biochemical function(s) of EIN3/EI L proteins, however, has remained unknown. In this study, we show that EIN3 and EILs comprise a family of novel sequence-specific DNA-binding proteins that regulate gene expression by binding directly to a primary ethylene re sponse element (PERE) related to the tomato E4-element. Moreover, we identi fied an immediate target of EIN3, ETHYLENE-RESPONSE-FACTOR1 (ERF1), which c ontains this element in its promoter. EIN3 is necessary and sufficient for ERF1 expression, and, like EIN3-overexpression in transgenic plants, consti tutive expression of ERF1 results in the activation of a variety of ethylen e response genes and phenotypes. Evidence is also provided that ERF1 acts d ownstream of EIN3 and all other components of the ethylene signaling pathwa y. The results demonstrate that the nuclear proteins EIN3 and ERF1 act sequ entially in a cascade of transcriptional regulation initiated by ethylene g as.