Ligand-induced Degradation of the Ethylene Receptor ETR2 through a Proteasome-dependent Pathway in Arabidopsis

Protein degradation plays an important role in modulating ethylene signal transduction in plants. Here we show that the ethylene receptor ETR2 is one such target for degradation and that its degradation is dependent upon perception of the signaling ligand ethylene. The ETR2 protein is initially induced by ethylene treatment, consistent with an increase in transcript levels. At ethylene concentrations above 1 μl/liter, however, ETR2 protein levels subsequently decrease in a post-transcriptional fashion. Genetic and chemical approaches indicate that ethylene perception by the receptors initiates the reduction in ETR2 protein levels. The ethylene-induced decrease in ETR2 levels is not affected by cycloheximide, an inhibitor of protein biosynthesis, but is affected by proteasome inhibitors, indicating a role for the proteasome in ETR2 degradation. Ethylene-induced degradation still occurs in seedlings treated with brefeldin A, indicating that degradation of ETR2 does not require exit from its subcellular location at the endoplasmic reticulum. These data support a model in which ETR2 is degraded by a proteasome-dependent pathway in response to ethylene binding. Implications of this model for ethylene signaling are discussed. Protein degradation plays an important role in modulating ethylene signal transduction in plants. Here we show that the ethylene receptor ETR2 is one such target for degradation and that its degradation is dependent upon perception of the signaling ligand ethylene. The ETR2 protein is initially induced by ethylene treatment, consistent with an increase in transcript levels. At ethylene concentrations above 1 μl/liter, however, ETR2 protein levels subsequently decrease in a post-transcriptional fashion. Genetic and chemical approaches indicate that ethylene perception by the receptors initiates the reduction in ETR2 protein levels. The ethylene-induced decrease in ETR2 levels is not affected by cycloheximide, an inhibitor of protein biosynthesis, but is affected by proteasome inhibitors, indicating a role for the proteasome in ETR2 degradation. Ethylene-induced degradation still occurs in seedlings treated with brefeldin A, indicating that degradation of ETR2 does not require exit from its subcellular location at the endoplasmic reticulum. These data support a model in which ETR2 is degraded by a proteasome-dependent pathway in response to ethylene binding. Implications of this model for ethylene signaling are discussed. Interactions between signaling ligands and membrane-bound receptors are essential for orchestrating the growth and development of multicellular eukaryotes. Ligand binding initiates signal transduction pathways that often culminate in the induction and repression of specific suites of genes. Studies of animal growth factor receptors have revealed that the release of bound ligands may not occur rapidly enough for physiologically relevant regulation of the pathways. Instead, the major method for regulating the amplitude and kinetics of signal transduction is via endocytosis of the ligand-receptor complexes (1Wiley H.S. Bittar E.E. Fundamentals of Medical Cell Biology. JAI Press Inc., Greenwich, CT1992Google Scholar, 2Sorkin A. Von Zastrow M. Nat. Rev. Mol. Cell. Biol. 2002; 3: 600-614Crossref PubMed Scopus (695) Google Scholar, 3Waterman H. Yarden Y. FEBS Lett. 2001; 490: 142-152Crossref PubMed Scopus (271) Google Scholar). Following endocytosis, receptors are sorted such that they either undergo degradation in the lysosome or are recycled back to the cell surface. Whether ligand-induced degradation of membrane receptors also occurs in plants has not been possible to determine until the relatively recent identification of cognate receptors for some plant growth factors. In plants, the gaseous hormone ethylene regulates seed germination, seedling growth, leaf and petal abscission, organ senescence, ripening, stress responses, and pathogen responses (4Abeles F.B. Morgan P.W. Saltveit Jr., M.E. Ethylene in Plant Biology. Academic Press, Inc., San Diego1992Google Scholar). Plant responses to ethylene have been found to occur over a range of ethylene concentrations from 0.2 nl/liter to 1000 μl/liter (4Abeles F.B. Morgan P.W. Saltveit Jr., M.E. Ethylene in Plant Biology. Academic Press, Inc., San Diego1992Google Scholar, 5Binder B.M. Mortimore L.A. Stepanova A.N. Ecker J.R. Bleecker A.B. Plant Physiol. 2004; 136: 2921-2927Crossref PubMed Scopus (118) Google Scholar, 6Chen Q.G. Bleecker A.B. Plant Physiol. 1995; 108: 597-607Crossref PubMed Scopus (117) Google Scholar). In Arabidopsis, ethylene is perceived by a five-member receptor family that includes ETR1, ETR2, ERS1, ERS2, and EIN4 (7Chang C. Stadler R. BioEssays. 2001; 23: 619-627Crossref PubMed Scopus (129) Google Scholar, 8Schaller G.E. Kieber J.J. Somerville C. Meyerowitz E. The Arabidopsis Book. American Society of Plant Biologists, Rockville, MD2002Google Scholar). The ethylene receptors have similar overall structures with transmembrane domains near their N termini and putative signaling motifs in their C-terminal halves. The transmembrane domains apparently serve two functions. First, they are responsible for membrane localization of the receptors, the receptor ETR1 having been demonstrated to localize to the endoplasmic reticulum (ER) 2The abbreviations used are: ERendoplasmic reticulumACC1-aminocyclopropane-1-carboxylatePMplasma membrane 2The abbreviations used are: ERendoplasmic reticulumACC1-aminocyclopropane-1-carboxylatePMplasma membrane (9Chen Y.F. Randlett M.D. Findell J.L. Schaller G.E. J. Biol. Chem. 2002; 277: 19861-19866Abstract Full Text Full Text PDF PubMed Scopus (243) Google Scholar). The ER is an unusual location for a hormone receptor but one compatible with the ready diffusion of ethylene in aqueous and lipid environments. Second, based on genetic and biochemical evidence, the transmembrane domains contain the ethylene-binding site (10Schaller G.E. Bleecker A.B. Science. 1995; 270: 1809-1811Crossref PubMed Scopus (453) Google Scholar, 11Rodriguez F.I. Esch J.J. Hall A.E. Binder B.M. Schaller G.E. Bleecker A.B. Science. 1999; 283: 996-998Crossref PubMed Scopus (489) Google Scholar). In the C-terminal half of each receptor are domains with similarity to histidine kinases and in some cases the receiver domains of response regulators. Histidine kinases and receiver domains are signaling elements originally identified as components in bacterial phosphorelays and are now known to be present in plants, fungi, and slime molds (12Schaller G.E. Adv. Bot. Res. 2000; 32: 109-148Crossref Google Scholar). endoplasmic reticulum 1-aminocyclopropane-1-carboxylate plasma membrane endoplasmic reticulum 1-aminocyclopropane-1-carboxylate plasma membrane The five-member family of Arabidopsis ethylene receptors contains two subfamilies based on phylogenetic analysis and some shared structural features (8Schaller G.E. Kieber J.J. Somerville C. Meyerowitz E. The Arabidopsis Book. American Society of Plant Biologists, Rockville, MD2002Google Scholar). Members of subfamily 1 (ETR1 and ERS1) contain three transmembrane domains and histidine kinase domains with all of the conserved residues required for histidine kinase activity (13Gamble R.L. Coonfield M.L. Schaller G.E. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 7825-7829Crossref PubMed Scopus (256) Google Scholar, 14Moussatche P. Klee H.J. J. Biol. Chem. 2004; 279: 48734-48741Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). Members of subfamily 2 (ETR2, ERS2, and EIN4) contain the three conserved transmembrane domains plus an additional N-terminal hydrophobic domain that is predicted to serve as a signal sequence. In addition, their histidine kinase domains lack residues essential for histidine kinase activity, and they have been proposed to act as Ser/Thr kinases (14Moussatche P. Klee H.J. J. Biol. Chem. 2004; 279: 48734-48741Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). Members from both subfamilies (ERS1, ETR2, and ERS2) are induced by ethylene at the transcriptional level (15Hua J. Sakai H. Nourizadeh S. Chen Q.G. Bleecker A.B. Ecker J.R. Meyerowitz E.M. Plant Cell. 1998; 10: 1321-1332Crossref PubMed Scopus (438) Google Scholar), indicating that the same ligand detected by the receptors also affects expression levels of the receptors. In this paper, we report on the biochemical characterization of ETR2, a member of subfamily 2 that has not been characterized previously at the protein level. Our results are consistent with a model whereby binding of ethylene to ETR2 induces degradation of the receptor, similar to what has been observed following ligand binding to animal growth factor receptors. But in contrast to the paradigm established with animal growth factor receptors, turnover of ethylene receptors is mediated by the proteasome rather than the lysosome, a situation potentially arising due to localization of receptors to the endoplasmic reticulum rather than to the plasma membrane. Plant Materials—Wild-type Arabidopsis (Columbia ecotype) and various ethylene response mutants were used, including ethylene-insensitive mutants (etr1-1, etr2-1, ein2-1) (16Chang C. Kwok S.F. Bleecker A.B. Meyerowitz E.M. Science. 1993; 262: 539-544Crossref PubMed Scopus (1187) Google Scholar, 17Sakai H. Hua J. Chen Q.G. Chang C. Medrano L.J. Bleecker A.B. Meyerowitz E.M. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 5812-5817Crossref PubMed Scopus (394) Google Scholar, 18Alonso J.M. Hirayama T. Roman G. Nourizadeh S. Ecker J.R. Science. 1999; 284: 2148-2152Crossref PubMed Scopus (951) Google Scholar), a constitutive ethylene response mutant ctr1-2 (19Kieber J.J. Rothenberg M. Roman G. Feldman K.A. Ecker J.R. Cell. 1993; 72: 427-441Abstract Full Text PDF PubMed Scopus (1463) Google Scholar), and receptor loss-of-function mutants (etr1-7 and etr2-3) (20Hua J. Meyerowitz E.M. Cell. 1998; 94: 261-271Abstract Full Text Full Text PDF PubMed Scopus (811) Google Scholar). The etr2-1; ctr1-2 and the etr1-1; ctr1-2 double mutants were generated by crossing, with plants homozygous for ctr1-2 identified by the constitutive ethylene response phenotype and those homozygous for etr2-1 and etr1-1 identified by PCR-based genotyping (20Hua J. Meyerowitz E.M. Cell. 1998; 94: 261-271Abstract Full Text Full Text PDF PubMed Scopus (811) Google Scholar). Plant Growth Conditions—For growth of etiolated seedlings, sterile seeds were placed on Petri dishes with half-strength Murashige and with and in the growth to ethylene by the a at were to at for were placed in and seedlings were for in the at in the of ethylene at the the growth of seedlings in the of the to of ethylene by the with inhibitors, seedlings were on placed on the and to the same the inhibitor and for the In cases to in aqueous plants were in G.E. Cell Biol. 1995; PubMed Scopus Google to for between growth and seeds were in Murashige and with with for Ethylene induced in seedlings by the of the 1-aminocyclopropane-1-carboxylate at 1 for Growth in the activity Res. PubMed Scopus Google and the levels of ethylene of by the of The proteasome and brefeldin were to the growth at the and concentrations of the ETR2 were of ETR2 with either a or a of the ETR2 H. Hua J. Chen Q.G. Chang C. Medrano L.J. Bleecker A.B. Meyerowitz E.M. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 5812-5817Crossref PubMed Scopus (394) Google by a a site and a a site The the to and the PubMed Scopus Google to The protein in and were to the by with and on The protein in E. and by binding to PubMed Scopus Google Scholar). from the protein by The were with with A. A. S. T. Morgan J.M. Science. PubMed Scopus Google Scholar). were with and the with 1 and and were from seedlings or plants in a at and with as (9Chen Y.F. Randlett M.D. Findell J.L. Schaller G.E. J. Biol. Chem. 2002; 277: 19861-19866Abstract Full Text Full Text PDF PubMed Scopus (243) Google Scholar, Schaller G.E. Plant Physiol. 2002; PubMed Scopus Google Scholar). the plant and at for The at for and the membrane in at 1 and with as (9Chen Y.F. Randlett M.D. Findell J.L. Schaller G.E. J. Biol. Chem. 2002; 277: 19861-19866Abstract Full Text Full Text PDF PubMed Scopus (243) Google Scholar). were identified by of the ER ETR1 and (9Chen Y.F. Randlett M.D. Findell J.L. Schaller G.E. J. Biol. Chem. 2002; 277: 19861-19866Abstract Full Text Full Text PDF PubMed Scopus (243) Google Scholar, A. Y. Plant Physiol. 1999; PubMed Scopus Google Scholar), the plasma membrane (9Chen Y.F. Randlett M.D. Findell J.L. Schaller G.E. J. Biol. Chem. 2002; 277: 19861-19866Abstract Full Text Full Text PDF PubMed Scopus (243) Google Scholar, A. Y. Plant Physiol. 1999; PubMed Scopus Google Scholar), the M. Plant Physiol. PubMed Scopus Google Scholar), the membrane A. Plant Physiol. 1993; PubMed Scopus Google Scholar), and the A. L.A. L.A. Plant Physiol. 1999; PubMed Scopus Google Scholar). were identified by analysis of levels G.E. Cell Biol. 1995; PubMed Scopus Google Scholar). were and as Schaller G.E. Plant Physiol. 2002; PubMed Scopus Google Scholar). In for ETR2 from seedlings in were an at and at in the same but with In were in of of and as Following 1 of at the by of from etiolated seedlings by the plant by with to the from three used as for a Inc., of and of and of on an a at by of and of each were specific for ETR2 and and and were generated and by which the method 2001; PubMed Scopus Google Scholar). with the to generated a of analysis has on ETR1, a member of subfamily that to be based on analysis of and protein levels. ETR2 is a member of subfamily based on is induced at the transcriptional level by ethylene (15Hua J. Sakai H. Nourizadeh S. Chen Q.G. Bleecker A.B. Ecker J.R. Meyerowitz E.M. Plant Cell. 1998; 10: 1321-1332Crossref PubMed Scopus (438) Google Scholar). ETR2 at the protein we and a The used to from and mutant Arabidopsis that been treated with either or ethylene μl/liter for The a protein of in the membrane of Arabidopsis, consistent with the of for The ETR2 receptor is induced by ethylene in and in the loss-of-function Ethylene induction of ETR2 is not affected by a loss-of-function mutant in ethylene receptor The of ethylene to ETR2 is in the ethylene-insensitive mutants etr2-1, and In ETR2 is present ethylene in the constitutive ethylene response mutant These data indicate that protein levels of the ethylene receptor ETR2 are by ethylene in plants and are consistent with transcriptional regulation previously (15Hua J. Sakai H. Nourizadeh S. Chen Q.G. Bleecker A.B. Ecker J.R. Meyerowitz E.M. Plant Cell. 1998; 10: 1321-1332Crossref PubMed Scopus (438) Google Scholar). protein levels of the ethylene receptor ETR1 are a receptor expression is not induced by ethylene. previously the ethylene-insensitive mutant etr1-1 is present at levels to ETR1 Schaller G.E. Plant Physiol. 2002; PubMed Scopus Google Scholar). previously found that the ethylene receptor ETR1 is to the ER membrane (9Chen Y.F. Randlett M.D. Findell J.L. Schaller G.E. J. Biol. Chem. 2002; 277: 19861-19866Abstract Full Text Full Text PDF PubMed Scopus (243) Google Scholar). determine ETR2 is to the we Arabidopsis by this we used the ctr1-2 mutant in which ETR2 is as as plants in which ETR2 induced by with the ethylene ER to dependent on they are with or be from the ER by of from the in a of the ER from to J.M. Scopus Google Scholar). were by for ETR2 as as for the membrane ETR1 and and used as a for the ETR2 a similar to ETR1 and from the membrane consistent with localization of ETR2 to the Ethylene of ethylene response analysis of ETR2 protein in the that ETR2 is induced at ethylene concentrations in a consistent with an increase in transcript levels But at ethylene concentrations above 1 μl/liter, the levels of ETR2 protein in a of the which In addition, a revealed that in ETR2 expression occur in response to with μl/liter ethylene that be by transcriptional Ethylene in an increase in ETR2 levels consistent with levels of by a decrease in ETR2 protein levels that of the expression levels. the and are consistent with post-transcriptional regulation of ETR2 the same a on ETR1 expression at the protein and levels not transcriptional and post-transcriptional upon we the of ethylene upon expression of ETR2 in the ctr1-2 mutant results in constitutive of ethylene responses in the plant (19Kieber J.J. Rothenberg M. Roman G. Feldman K.A. Ecker J.R. Cell. 1993; 72: 427-441Abstract Full Text PDF PubMed Scopus (1463) Google Scholar), including constitutive expression of ETR2 one is to in ETR2 expression that in transcript levels of the Ethylene analysis a reduction in ETR2 protein levels with levels of a reduction observed at ethylene concentrations of μl/liter and is above 1 μl/liter In in levels were for the receptors, as predicted the mutant the ethylene-induced decrease in ETR2 levels occurs analysis that the ethylene upon ETR2 expression be observed 1 of ethylene Ethylene by the of used both chemical and genetic approaches to that the ligand-induced turnover of ETR2 results from ethylene perception by the receptors. a required by the receptors for binding in ethylene F.I. Esch J.J. Hall A.E. Binder B.M. Schaller G.E. Bleecker A.B. Science. 1999; 283: 996-998Crossref PubMed Scopus (489) Google Scholar). The etr2-1 and the etr1-1 mutants are both the predicted ethylene-binding of the receptors that in ethylene H. Hua J. Chen Q.G. Chang C. Medrano L.J. Bleecker A.B. Meyerowitz E.M. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 5812-5817Crossref PubMed Scopus (394) Google Scholar, C. Meyerowitz E.M. Proc. Natl. Acad. Sci. U. S. A. 1995; PubMed Scopus Google Scholar). of plants with or of either the etr2-1 or the etr1-1 the ethylene-induced turnover of ETR2 protein ethylene perception by the receptors initiates the ethylene-induced decrease in ETR2 protein levels. These data also indicate that at the ethylene level that this is not a of ethylene upon protein expression but due to between ethylene and the receptors. data indicate that the turnover of one member of the receptor family be by the of member of the family to a situation of the ethylene-insensitive mutant etr2-1 the of ETR1 for Plant Physiol. 2002; PubMed Scopus Google Scholar). Ethylene of upon receptor levels be due to regulation of regulation of protein degradation. between we the of the protein inhibitor as as proteasome upon the ligand-induced decrease in ETR2 levels. for the of turnover in the of the that the of ethylene upon the we an of ethylene upon ETR2 levels. still observed the ethylene-induced decrease in ETR2 protein levels following in of seedlings with cycloheximide, indicating that the of ethylene (9Chen Y.F. Randlett M.D. Findell J.L. Schaller G.E. J. Biol. Chem. 2002; 277: 19861-19866Abstract Full Text Full Text PDF PubMed Scopus (243) Google Scholar). with a we found that in of seedlings with two proteasome inhibitors, and Y. S. R. L.J. Chen H. Plant Physiol. PubMed Scopus Google Scholar), the of ethylene to levels of ETR2 These data support a model in which ETR2 is degraded by a proteasome-dependent pathway in response to ethylene binding. of that degradation of ETR2 at its subcellular location on the ER membrane. First, we found that ETR2 be degraded in in degradation is to and the proteasome and that ETR2 degradation may occur due to with the ER membrane. that degradation occurs at the ER by in of ctr1-2 seedlings with the inhibitor brefeldin J. G. 2001; PubMed Scopus Google Scholar). degradation of ETR2 still observed following with brefeldin that this does not require of ETR2 from the ER to of the such as the or data indicate that protein degradation plays a major role in the regulation of ethylene and signal of an in ethylene biosynthesis, are by protein degradation H. C. Ecker J.R. 2004; PubMed Scopus Google Scholar). of a factor in the ethylene signaling are also by protein levels in the of ethylene T. E. Y. S. S. C. P. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar, H. Ecker J.R. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar, S. J. PubMed Scopus Google Scholar, J.M. J. J.M. S. Proc. Natl. Acad. Sci. U. S. A. 2004; Scopus Google Scholar). In both a proteasome-dependent pathway has been in regulating the protein levels. Our results that levels of the ethylene receptor ETR2 are also by protein but in this ethylene induces degradation of the The post-transcriptional of ethylene on ETR2 levels is at ethylene concentrations above 1 μl/liter, an ethylene of ethylene responses occur from 0.2 nl/liter to 1000 μl/liter (4Abeles F.B. Morgan P.W. Saltveit Jr., M.E. Ethylene in Plant Biology. Academic Press, Inc., San Diego1992Google Scholar, 5Binder B.M. Mortimore L.A. Stepanova A.N. Ecker J.R. Bleecker A.B. Plant Physiol. 2004; 136: 2921-2927Crossref PubMed Scopus (118) Google Scholar, 6Chen Q.G. Bleecker A.B. Plant Physiol. 1995; 108: 597-607Crossref PubMed Scopus (117) Google Scholar). Arabidopsis seedlings show a response to ethylene at than μl/liter, transcriptional have been to occur in Arabidopsis over a range of ethylene concentrations from to 1000 μl/liter Q.G. Bleecker A.B. Plant Physiol. 1995; 108: 597-607Crossref PubMed Scopus (117) Google Scholar). ethylene that μl/liter (4Abeles F.B. Morgan P.W. Saltveit Jr., M.E. Ethylene in Plant Biology. Academic Press, Inc., San Diego1992Google Scholar), an ethylene to in in the levels of receptors similar occur plant detected a decrease in ETR2 levels in at ethylene concentrations above 1 μl/liter, but turnover may still occur at ethylene concentrations but not be as detected by of at the ethylene turnover of ETR2 may be due to the of receptors over of ethylene upon and of Our analysis of ETR2 in the that turnover may occur at μl/liter ethylene. degradation occur by either or In a the act of ethylene binding a in the receptor that the receptor to to degradation. In an ethylene binding the signal transduction pathway to ethylene responses, one possible response the induction of a factor that receptor Our data support the with the of ethylene with ETR2 of the by which degradation of the receptor is potentially by a in the is based on analysis of the ctr1-2 which is of ethylene responses in the of bound of ETR2 not occur in the ctr1-2 seedlings were treated with ethylene. degradation of ETR2 in the ctr1-2 be by ethylene perception either chemical or genetic receptor These the receptor the that has in the of such that ethylene a in the protein (7Chang C. Stadler R. BioEssays. 2001; 23: 619-627Crossref PubMed Scopus (129) Google Scholar, 8Schaller G.E. Kieber J.J. Somerville C. Meyerowitz E. The Arabidopsis Book. American Society of Plant Biologists, Rockville, MD2002Google Scholar). ethylene-induced in of the receptor may be for degradation. degradation of ethylene receptors is to a role in the of as has been found on binding of ligands to animal growth factor receptors (1Wiley H.S. Bittar E.E. Fundamentals of Medical Cell Biology. JAI Press Inc., Greenwich, CT1992Google Scholar, 2Sorkin A. Von Zastrow M. Nat. Rev. Mol. Cell. Biol. 2002; 3: 600-614Crossref PubMed Scopus (695) Google Scholar, 3Waterman H. Yarden Y. FEBS Lett. 2001; 490: 142-152Crossref PubMed Scopus (271) Google Scholar). ethylene receptors ethylene the for of ethylene from ETR2 based on its analysis in (10Schaller G.E. Bleecker A.B. Science. 1995; 270: 1809-1811Crossref PubMed Scopus (453) Google Scholar, F.I. Esch J.J. Binder B.M. P. Klee H.J. Bleecker A.B. Plant J. PubMed Scopus Google Scholar). ligand-induced the plant receptors with bound ethylene that are to in the ethylene These complexes be as based on the model for ethylene to this upon binding the receptors the kinase Y. H. J. Kieber J.J. Plant J. PubMed Scopus Google Scholar, Chen Y.F. Randlett M.D. Findell J.L. Kieber J.J. Schaller G.E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus (256) Google Scholar, Chang C. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). as a of ethylene its repression of the pathway that ethylene responses are receptor with bound ethylene is to activity and in the signaling of the ligand-receptor for its by receptors that activity, the plant to ethylene. The decrease in ethylene receptor levels from ligand-induced turnover may also have for the of the ethylene of the regulation in the ethylene pathway a decrease in overall ethylene receptor levels in of plants to such that a of ethylene is for a response Plant Physiol. 2002; PubMed Scopus Google Scholar, Klee H.J. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar). of ethylene receptors are the induction of ethylene responses occur in the of ethylene (20Hua J. Meyerowitz E.M. Cell. 1998; 94: 261-271Abstract Full Text Full Text PDF PubMed Scopus (811) Google Scholar). is also possible that the of a specific of receptors may serve to for such a the for subfamily and receptors in signaling Hall A.E. R. Bleecker A.B. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google the specific role for receptors with receiver in seedling growth ethylene B.M. J.M. B.M. Bleecker A.B. Plant Physiol. 2004; 136: PubMed Scopus (129) Google Scholar). of ethylene receptors in release of the bound one that the kinetics for ethylene from Arabidopsis a ethylene than the release kinetics observed ethylene receptors are in (10Schaller G.E. Bleecker A.B. Science. 1995; 270: 1809-1811Crossref PubMed Scopus (453) Google Scholar, F.I. Esch J.J. Binder B.M. P. Klee H.J. Bleecker A.B. Plant J. PubMed Scopus Google Scholar). of the ethylene release kinetics in plants this Hall Scopus Google Scholar, The Plant Press, Inc., Scholar). of than and release kinetics of or for ethylene have been found in Arabidopsis as as in plants Hall Scopus Google Scholar, The Plant Press, Inc., Scholar). These in the release kinetics may to in the of turnover to of the ethylene receptor based on their to ligand-induced we that the release kinetics for ethylene found in Arabidopsis be due to degradation of ETR2, the release kinetics be due to degradation of Our results show that ETR2 is to degradation the animal growth factor receptors but with degradation of animal growth factor receptors endocytosis of the receptor and to the lysosome A. Von Zastrow M. Nat. Rev. Mol. Cell. Biol. 2002; 3: 600-614Crossref PubMed Scopus (695) Google Scholar, 3Waterman H. Yarden Y. FEBS Lett. 2001; 490: 142-152Crossref PubMed Scopus (271) Google Scholar). is apparently by of the receptor, which as a signal for the of ETR2, in contrast to the paradigm established for animal growth factor receptors, is mediated by the a situation potentially arising due to localization of ETR2 to the ER rather than to the plasma membrane the ethylene receptors not have the subcellular localization for of ETR2 does not require of ETR2 to in the and degradation via the is to ETR2 degradation. degradation is known for its role in the degradation of and membrane of the C. E. T. Nat. Cell Biol. PubMed Scopus Google Scholar), but has also been found to turnover of such as ETR2, is an membrane protein of the ER C. E. T. Nat. Cell Biol. PubMed Scopus Google Scholar). that ethylene binding to its receptor at the endoplasmic reticulum results in a for on the domain of ETR2, by degradation at the