The ethylene signaling pathway: New insights

Current Opinion in Plant Biology

Volumn 7, Issue 1, 2004, Pages 40-49

  Guo, Hongwei ^a   Ecker, Joseph R ^a  

^a SALK INSTITUTE FOR BIOLOGICAL STUDIES   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ARABIDOPSIS;

EID: 1642523244     PISSN: 13695266     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.pbi.2003.11.011     Document Type: Review

References (51)

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20. Cancel J.D., Larsen P.B. Loss-of-function mutations in the ethylene receptor ETR1 cause enhanced sensitivity and exaggerated response to ethylene in Arabidopsis. Plant Physiol. 129:2002;1557-1567 A careful re-examination of LOF etr1 mutants revealed that these plants show enhanced sensitivity to ethylene. The authors also showed that a type-II receptor, ETR2, can weakly interact with the amino-terminal domain of CTR1 in yeast two-hybrid assays and pull-down experiments.
21. Wang W., Hall A.E., O'Malley R., Bleecker A.B. Canonical histidine kinase activity of the transmitter domain of the ETR1 ethylene receptor from Arabidopsis is not required for signal transmission. Proc Natl Acad Sci USA. 100:2003;352-357 The authors isolated a LOF T-DNA insertion mutation in ERS1. The loss of two type-I receptors in etr1 ers1 double mutants conferred strong constitutive-ethylene response phenotypes, implying that type-I receptors play a special role in ethylene signaling. Because all type-II receptors are predicted to lack a histidine kinase activity, the etr1 ers1 double mutant provided a platform from which to test whether a histidine kinase activity is required for hormone perception. The expression of each of the five ethylene receptors under an ETR1 promoter in the etr1 ers1 background indicated that only type-I receptors (i.e. ETR1 or ERS1) can rescue the double mutant phenotype. However, a mutant form of ETR1 that lacks the histidine kinase activity was able to function like wildtype ETR1, ruling out the requirement of a histidine kinase activity for type-I receptor signaling.
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23. Hall A.E., Bleecker A.B. Analysis of combinatorial loss-of-function mutants in the Arabidopsis ethylene receptors reveals that the ers1 etr1 double mutant has severe developmental defects that are EIN2 dependent. Plant Cell. 15:2003;2032-2041 The authors carried out a further characterization of etr1 ers1 double mutants and comparisons with other constitutive ethylene response mutants. etr1 ers1 mutants exhibited delayed flowering, and defects in fertility and flower morphology. Despite these adult phenotypes, etr1 ers1 etiolated seedlings only showed a partial constitutive triple response and were still responsive to ethylene treatment. Importantly, all of the defects could be completely suppressed by the ein2 mutation, and thus they represent authentic ethylene response phenotypes.
24. Gamble R.L., Qu X., Schaller G.E. Mutational analysis of the ethylene receptor ETR1. Role of the histidine kinase domain in dominant ethylene insensitivity. Plant Physiol. 128:2002;1428-1438 The role of histidine kinase activity in the dominant ethylene-insensitivity mutant etr1-1 was investigated. Disruption of His kinase activity had no effect on etr1-1 function, suggesting that His kinase activity is not required for receptor signaling. Furthermore, deletion of the entire carboxy-terminal half of ETR1, the including His kinase domain and the receiver domain, had little effect on etr1-1 (dominant) function, although a lack of endogenous ETR1 seemed to suppress it slightly. These findings led the authors to speculate that the amino-terminal half of etr1-1 is able to impose an ethylene-insensitive state upon other wildtype receptors through heterodimerization.
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29. 2+- dependent density shift as BiP. The third line of evidence came from immunogold electron microcopy. Gold granules representing ETR1 were detected on the ER. The authors further showed that the ER localization of ETR1 was determined by its amino-terminal ethylene-binding domain, but was not affected by ethylene binding or etr1-1 dominant mutation.
30. Gao Z., Chen Y.F., Randlett M.D., Zhao X.C., Findell J.L., Kieber J.J., Schaller G.E. Localization of the Raf-like kinase CTR1 to the endoplasmic reticulum of Arabidopsis through participation in ethylene receptor signaling complexes. J Biol Chem. 278:2003;34725-34732 This work provides possible mechanistic insight into the regulation of CTR1 by the ethylene receptors. Analysis that was based on sucrose-density-gradient fractionation showed that CTR1 was primarily localized to the ER. The ER localization of CTR1 was dependent upon the presence of ethylene receptors. A mutation in CTR1 that eliminates ETR1 binding resulted in the dissociation of CTR1 from the ER. An in-vivo association between ETR1 and CTR1 was demonstrated by affinity co-purification. Moreover, an in-vitro pull-down assay revealed that CTR1 binds to the carboxy-terminal half of ETR1, but a histidine kinase activity was not required for CTR1-ETR1 interaction. The authors proposed a model for signaling by the ethylene receptor-CTR1 complex in which CTR1 is activated by association with the ER-bound receptors.
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32. Huang Y., Li H., Hutchison C.E., Laskey J., Kieber J.J. Biochemical and functional analysis of CTR1, a protein kinase that negatively regulates ethylene signaling in Arabidopsis. Plant J. 33:2003;221-233 CTR1 was shown to function as a Ser/Thr kinase. A missense mutation (CTR1-8) in the amino-terminal domain of CTR1 resulted in the loss of most CTR1 function. Yeast two-hybrid assays revealed that the amino-terminal domain of wildtype CTR1, but not of CTR1-8, can interact with ETR1. Overexpression of the amino-terminal domain of wildtype CTR1 caused a dominant negative effect whereas the CTR1-8 mutation disrupted this effect. These data suggested that CTR1 associates with ETR1 in vivo and that this association is required for CTR1 function.
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35. Ouaked F., Rozhon W., Lecourieux D., Hirt H. A MAPK pathway mediates ethylene signaling in plants. EMBO J. 22:2003;1282-1288 The authors provide the first biochemical evidence to suggest the involvement of a MAPK cascade in the ethylene response pathway. They showed that the kinase activities of two Medicago MAPKs, the Arabidopsis MPK6, and a Medicago MAPKK that activates these MAPKs, were activated by ethylene. The activation of Arabidopsis MPK6 required the functions of ETR1 and CTR1, but not those of EIN2 and EIN3. Constitutive overexpression of the Medicago MAPKK in Arabidopsis caused a ctr1-like phenotype. Thus, a MAPK module is proposed to work downstream of CTR1 and to play a positive role in ethylene responses.
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39. ••].
40. Alonso J.M., Stepanova A.N., Solano R., Wisman E., Ferrari S., Ausubel F.M., Ecker J.R. Five components of the ethylene-response pathway identified in a screen for weak ethylene-insensitive mutants in Arabidopsis. Proc Natl Acad Sci USA. 100:2003;2992-2997 Five weak ethylene-insensitive mutants were isolated. Two of the mutated loci were allelic to previously identified mutations (ers1 and transport inhibitor response 1 [tir1]), two represented new mutations in previously unidentified ethylene pathway genes, and one was the eil1 mutation. ein3 eil1 double mutants showed a complete ethylene insensitivity in many known ethylene responses, including the triple response and pathogen resistance, as well as the ability to fully suppress the ctr1 mutation. These results demonstrate the essential role of EIN3/EIL1 in myriad ethylene responses.
41. Alonso J.M., Stepanova A.N., Leisse T.J., Kim C.J., Chen H., Shinn P., Stevenson D.K., Zimmerman J., Barajas P., Cheuk R.et al. Genome-wide insertional mutagenesis of Arabidopsis thaliana. Science. 301:2003;653-657 The authors of this paper reported the creation of genome-wide Arabidopsis T-DNA insertion lines whose precise locations have been determined. In addition, a whole-genome gene expression study using an Affymetrix microarray identified 628 ethylene-regulated genes. Taking advantage of the availability of the sequence-indexed insertion mutant database and the gene expression profile, the authors isolated several insertion mutations in four related ethylene-inducible ERF genes, called EDF genes. Although plants that carried mutations in just one of these genes had no ethylene response defects, multiple-mutant plants exhibited significant ethylene-insensitive phenotypes. This is the first genetic evidence based on the study of LOF ERF mutants to demonstrate that the ERF family of transcription factors function in ethylene responses with a high degree of functional redundancy.
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50. Lorenzo O., Piqueras R., Sanchez-Serrano J.J., Solano R. ETHYLENE RESPONSE FACTOR1 integrates signals from ethylene and jasmonate pathways in plant defense. Plant Cell. 15:2003;165-178 Ethylene and JA have been shown to induce several plant defense genes synergistically. This study defined a previously isolated ethylene response factor, ERF1, as a common downstream component of two hormone response pathways. ERF1 expression was induced by both hormones, and this induction required the concurrent existence of both signaling pathways. Overexpression of ERF1 suppressed the defense response defects observed in JA-insensitive mutants. Global gene expression analysis showed that many ethylene-/JA-regulated genes are constitutively activated in ERF-overexpressing plants. Thus, ERF1 is demonstrated to be a key factor in the integration of two hormone signals.
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