【正文】 nts result in a loss of ERlocalization of CTR1. Taken together, these data suggested that the receptors and CTR1 function as part of an ERlocalized plex that actively represses ethylene responses. ● The serine/threonine kinase activity of CTR1 was demonstrated in vitro and shown to be essential for proper functioning of the receptors/CTR1 signaling plex. It has been established that ethylene binding to the receptors affects neither the interaction between the receptors and CTR1 nor their subcellular localization. The current proposed model predicts that upon ethylene binding, the receptors/ CTR1 signaling plexes are turned ‘‘off’’ . 4. A unique plant protein is a central ponent of the signaling pathway and positively regulates ethylene responses ● Downstream of the receptors/CTR1 plexes there acts a positive regulator of the pathway, ETHYLENE INSENSITIVE2 (EIN2). EIN2 is required for all ethylene responses studied and constitutes a critical step in the signal transduction. The hydrophobic aminoterminus is predicted to form twelve transmembrane domains and shares sequence similarity with the family of NRAMP metal ion transporters. ● The long EIN2 carboxylterminus contains a coiledcoil structure (a motif typically involved in protein–protein interactions) but otherwise displays no similarity to known protein . Conversely, the NRAMPlike aminoterminal domain of EIN2 is believed to ‘‘sense’’ the upstream signaling events. 5. A transcriptional cascade mediates ethylene responses at the gene expression level ● ETHYLENE INSENSITIVE3, EIN3, is a nuclearlocalized protein required for ethylene signaling that geically works downstream of EIN2. EIN3 belongs to a small gene family that in Arabidopsis also includes five EIN3LIKE (EIL) proteins. These observations suggested that EIN3 and at least some of the EILs may act as transcriptional regulators of ethylene responses. ● In Arabidopsis, EIN3, EIL1, and EIL2 were demonstrated to bind to a short palindromic region, known as the EIN3binding site, or EBS, in the promoter of the EREBP family member ETHYLENE RESPONSE FACTOR1 (ERF1). ERF1, in turn, is a GCC boxbinding transcription factor that acts downstream of EIN3 and EILs and is responsible for the modulation of a set of secondary ethylene responsive genes. Consistent with these results, transgenic lines overexpressing EIN3 show a constitutive triple response, whereas in ERF1overexpressing plants only some of the ethylene responses are activated. ● ERF1 is also required for the activation of defenserelated responses by the plant hormone jasmonic acid. Moreover, both ethylene and jasmonate pathways must be intact for proper ERF1 expression. Ethylene and jasmonate interact synergistically to achieve maximal expression of ERF1. This transcription factor, therefore, represents a critical element in the interaction between these two important hormones. 6. The ubiquitin/26S proteasome pathway regulates EIN3 activity ● A recently emerging picture positions the SCFE3 ligases in the center of many plant hormone signaling pathways, including those of auxin, gibberellins, and jasmonic acid. ● The ethylene signaling pathway also employs the SCF/26S proteasome to regulate the levels of at least one of its ponents, EIN3. Recently, two Fbox proteins, EIN3 BINDING FACTOR1 (EBF1) and EBF2, were shown to act as part of an E3ligase and to bind and target the constitutively produced EIN3 for degradation in the absence of ethylene. ● In the presence of exogenous ethylene, EIN3 protein levels were found to increase. ● In addition to the negative regulation by EBF1 and EBF2, a stimulatory mechanism that activates the stabilized EIN3 protein is also expected to participate in the regulation of the activity of this critical transcription factor. This observation is supported by the ethylene responsiveness of EIN3overexpression lines and ebf1。eil1 double mutants display almost plete insensitivity to the ethylene gas. In addition, regulation of EIN3 by the SCF/26S proteasome pathway serves as an efficient mechanism for the prompt and finetuned control of this transcriptional cascade. ● In order to gain a better understanding of the ethylene effects in transcription, several research groups have performed genomescale studies using microarrays and other highthroughput techniques. ● Early studies relied on cDNA microarrays covering only a fraction of the genome, and thus Schenk and coworkers analyzed the expression of