【正文】 2375 ESTs enriched in putative defenserelated genes. Interestingly, the authors evaluated the pattern of gene expression in response not only to ethylene, but also to a fungal pathogen, salicylic acid, and jasmonate. A high level (50%) of coordinated gene expression was observed for the ethylene and jasmonate treatments. ● This initial study was followed by a broader analysis of ethylene responses relying on an EST microarray representing 6 000 unique genes. The authors also took advantage of the ethylene mutants etr11 and ctr11 as controls. The parative analysis of the profiles identified approximately 7% of genes as ethyleneregulated. Ethylene was also found to change expression levels of known jasmonate and auxinregulated genes, indicative of the interaction between ethylene and these hormones. ● A hierarchical cluster analysis of the data revealed distinct subsets of genes with correlated patterns of expression. These included: (1) a group of very early, transiently inducible genes (after 10 to 30 min of the beginning of the treatment), (2) an earlyinducible subset (30 min to 1 h), (3) a group of genes upregulated at the intermediate (between 1–6 h of ethylene exposure) timepoints, and (4) a group consisting of lateinducible genes (at 6 h of treatment). A large number of clones also displayed higher expression levels in the ein21 ethylene insensitive background and were downregulated in wildtype ethylenetreated plants. ● One of the novelties in the study by De Paepe and coworkers55 was the discovery of an ethylenemediated regulation of the genes involved in the ubiquitin/26S proteasome pathway. These results were further confirmed by RTPCR analysis, which revealed three ubiquitinspecific proteases and an ubiquitin conjugating enzyme as being upregulated by the ethylene treatment. It is possible that these genes work in coordination with the wellcharacterized EBF1 and EBF2. ● The physiological significance of the interaction between ethylene and glucose, as well as the in planta role of EIN3 in the crosstalk of these two signals, awaits further experimental confirmation. ● Most importantly, hormone crosstalk has also emerged as a prominent theme in these analyses, particularly, the interaction between ethylene and jasmonate in plant defense responses leading to the identification of several mon target genes. ● In addition to coregulating a number of target genes, the ethylenejasmonate and ethyleneauxin interactions were also suggested to take place at the level of hormone biosynthesis. Interestingly, the recent characterization of two ethylene insensitive mutants with altered auxin biosynthesis not only supports the importance of the ethyleneauxin interaction, but provides a clear evidence of its physiological significance. Fig. 4 Simplified diagram of hormonal crosstalk in plants, as based on the current knowledge of the interactions between ethylene and other plant hormones in Arabidopsis. Three basic levels of interactions are presently known. (1) Hormones may influence the synthesis of each other through the mutual regulation of expression or activity of key biosynthetic genes, as in the case of ethylene and auxin. (2) Crosstalk may be achieved through sharing of mon ponents of the signal transduction machineries, as exemplified by ERF1 in the ethylene– jasmonate crosstalk. (3) Signals may converge on the regulation of expression of mon target genes, an interaction mode exhibited by both ethylene–auxin and ethylene–jasmonate crosstalks. ● For a more detailed review with emphasis on ethylene interactions with other plant hormones, the reader is referred to a recent review. ● Future ethylene signaling research will most likely focus on uncovering the remaining signaling ponents, as well as on dissecting the regulatory mechanisms that finetune this crucial signal transduction pathway in plants, from hormone perception by the receptors, to signal transmission through CTR1, EIN2, and the transcriptional cascade initiated by EIN3. ● Due to the key role of transcriptional control in mediating ethylene responses at the wholeplant level, genomewide studies of gene expression profiles will certainly bee critical for the indepth understanding of this hormone action. ● This plex web of hormonal interactions is an essential system employed by plants to integrate and properly respond to endogenous and environmental signals modulating their growth, development, and reproduction.