Journal of Biological Chemistry · 2009 · 73 citations · 52 references
Life SciencesPlant BiologyPlant SciencesPlant BiochemistryPlant Molecular BiologyPlant PhysiologyChannel StructureIon Channel ExpressionIon Channel PhysiologyIon Channel RegulationIon ChannelsPotassium Channel BiophysicsChannelsGuard Cell Ion TransportGuard Cell PhysiologyPatch-clamp AnalysisPatch-clamp RecordingPotassium Channel FunctionPotassium Channel GatingPotassium Channel Regulation
Guard cells adjust their volume by changing their ion content due to intense fluxes that, for K+, are believed to flow through inward or outward Shaker channels. Because Shaker channels can be homo- or heterotetramers and Arabidopsis guard cells express at least five genes encoding inward Shaker subunits, including the two major ones, KAT1 and KAT2, the molecular identity of inward Shaker channels operating therein is not yet completely elucidated. Here, we first addressed the properties of KAT1-KAT2 heteromers by expressing KAT1-KAT2 tandems in Xenopus oocytes. Then, computer analyses of the data suggested that coexpression of free KAT1 and KAT2 subunits resulted mainly in heteromeric channels made of two subunits of each type due to some preferential association of KAT1-KAT2 heterodimers at the first step of channel assembly. This was further supported by the analysis of KAT2 effect on KAT1 targeting in tobacco cells. Finally, patch-clamp recordings of native inward channels in wild-type and mutant genotypes strongly suggested that this preferential heteromerization occurs in planta and that Arabidopsis guard cell inward Shaker channels are mainly heteromers of KAT1 and KAT2 subunits. Guard cells adjust their volume by changing their ion content due to intense fluxes that, for K+, are believed to flow through inward or outward Shaker channels. Because Shaker channels can be homo- or heterotetramers and Arabidopsis guard cells express at least five genes encoding inward Shaker subunits, including the two major ones, KAT1 and KAT2, the molecular identity of inward Shaker channels operating therein is not yet completely elucidated. Here, we first addressed the properties of KAT1-KAT2 heteromers by expressing KAT1-KAT2 tandems in Xenopus oocytes. Then, computer analyses of the data suggested that coexpression of free KAT1 and KAT2 subunits resulted mainly in heteromeric channels made of two subunits of each type due to some preferential association of KAT1-KAT2 heterodimers at the first step of channel assembly. This was further supported by the analysis of KAT2 effect on KAT1 targeting in tobacco cells. Finally, patch-clamp recordings of native inward channels in wild-type and mutant genotypes strongly suggested that this preferential heteromerization occurs in planta and that Arabidopsis guard cell inward Shaker channels are mainly heteromers of KAT1 and KAT2 subunits. IntroductionStomata are microscopic pores in the plant leaf epidermis that allow both diffusion of atmospheric CO2 toward the inner photosynthetic tissues and water vapor loss by transpiration. Regulation of stomatal aperture allows plants to cope with the conflicting needs of enabling CO2 entry for photosynthesis and of preventing excessive water loss and desiccation. Stomatal movement results from a change in turgor of the two guard cells surrounding the pore. An increase or decrease in turgor opens or closes the stoma, respectively. This osmoregulation process involves K+ transport into and from the guard cells, which are mediated mainly by potassium channels in the plasma membrane belonging to the Shaker family (1.Lebaudy A. Véry A.A. Sentenac H. FEBS Lett. 2007; 581: 2357-2366Crossref PubMed Scopus (241) Google Scholar, 2.Ward J.M. Mäser P. Schroeder J.I. Annu. Rev. Physiol. 2009; 71: 59-82Crossref PubMed Scopus (275) Google Scholar). These potassium channels were found to play pleiotropic roles in guard cells, improving stomatal reactivity to external or internal signals (light, CO2 availability, or evaporative demand) and thus enhancing the ability of the plant to adapt to fluctuating and/or stressing natural environments (1.Lebaudy A. Véry A.A. Sentenac H. FEBS Lett. 2007; 581: 2357-2366Crossref PubMed Scopus (241) Google Scholar).Plant Shaker-like K+ channels are tetrameric proteins built of four α-subunits. Each subunit consists of a hydrophobic core flanked by cytosolic N- and C-terminal regions. The hydrophobic core is composed of six transmembrane segments (S1–S6). The loop between S5 and S6 (P domain) contributes to the permeation pathway of the channel and carries the hallmark GYG(D/E) motif of highly K+-selective channels. The fourth transmembrane segment (S4) contains positively charged amino acids and is involved in the voltage-sensing process of the Shaker-like K+ channels. Hyperpolarization-activated channels mediate inward K+ currents, and depolarization- activated ones mediate outward K+ currents (3.Dreyer I. Blatt M.R. Trends Plant Sci. 2009; 14: 383-390Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar). More generally, the activity of Shaker-like K+ channels is regulated at both the transcriptional and post-translational levels. Large variations in transcript levels have been observed in response to different environmental and hormonal factors such as light, abscisic acid, auxin, and salt stress (4.Véry A.A. Sentenac H. Annu. Rev. Plant Biol. 2003; 54: 575-603Crossref PubMed Scopus (454) Google Scholar). At the post-translational level, channel activity is controlled by intracellular factors such as H+ (5.Lacombe B. Pilot G. Gaymard F. Sentenac H. Thibaud J.B. FEBS Lett. 2000; 466: 351-354Crossref PubMed Scopus (72) Google Scholar, 6.Lacombe B. Pilot G. Michard E. Gaymard F. Sentenac H. Thibaud J.B. Plant Cell. 2000; 12: 837-851PubMed Google Scholar) and cyclic nucleotides (7.Hoshi T. J. Gen. Physiol. 1995; 105: 309-328Crossref PubMed Scopus (195) Google Scholar, 8.Gaymard F. Cerutti M. Horeau C. Lemaillet G. Urbach S. Ravallec M. Devauchelle G. Sentenac H. Thibaud J.B. J. Biol. Chem. 1996; 271: 22863-22870Abstract Full Text Full Text PDF PubMed Scopus (144) Google Scholar). In addition, there is strong evidence that also interacting regulatory proteins, e.g. kinases and phosphatases, dynamically modify channel activity (9.Michard E. Dreyer I. Lacombe B. Sentenac H. Thibaud J.B. Plant J. 2005; 44: 783-797Crossref PubMed Scopus (72) Google Scholar, 10.Michard E. Lacombe B. Porée F. Mueller-Roeber B. Sentenac H. Thibaud J.B. Dreyer I. J. Gen. Physiol. 2005; 126: 605-617Crossref PubMed Scopus (47) Google Scholar, 11.Xu J. Li H.D. Chen L.Q. Wang Y. Liu L.L. He L. Wu W.H. Cell. 2006; 125: 1347-1360Abstract Full Text Full Text PDF PubMed Scopus (715) Google Scholar, 12.Li L. Kim B.G. Cheong Y.H. Pandey G.K. Luan S. Proc. Natl. Acad. Sci. U.S.A. 2006; 103: 12625-12630Crossref PubMed Scopus (334) Google Scholar, 13.Luan S. Trends Plant Sci. 2009; 14: 37-42Abstract Full Text Full Text PDF PubMed Scopus (399) Google Scholar, 14.Luan S. Lan W. Chul Lee S. Curr. Opin. Plant Biol. 2009; 12: 339-346Crossref PubMed Scopus (150) Google Scholar, 15.Geiger D. Becker D. Vosloh D. Gambale F. Palme K. Rehers M. Anschuetz U. Dreyer I. Kudla J. Hedrich R. J. Biol. Chem. 2009; 284: 21288-21295Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar). Interestingly, the tetrameric structure of the channels provides another level of control of their functional properties. A functional channel can be formed not only by the assembly of four identical subunits (homomeric channels) but also by polypeptides encoded by different Shaker-like K+ channel genes (15.Geiger D. Becker D. Vosloh D. Gambale F. Palme K. Rehers M. Anschuetz U. Dreyer I. Kudla J. Hedrich R. J. Biol. Chem. 2009; 284: 21288-21295Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 16.Dreyer I. Antunes S. Hoshi T. Müller-Röber B. Palme K. Pongs O. Reintanz B. Hedrich R. Biophys. J. 1997; 72: 2143-2150Abstract Full Text PDF PubMed Scopus (143) Google Scholar, 17.Baizabal-Aguirre V.M. Clemens S. Uozumi N. Schroeder J.I. J. Membr. Biol. 1999; 167: 119-125Crossref PubMed Scopus (58) Google Scholar, 18.Ache P. Becker D. Deeken R. Dreyer I. Weber H. Fromm J. Hedrich R. Plant J. 2001; 27: 571-580Crossref PubMed Google Scholar, 19.Pilot G. Lacombe B. Gaymard F. Chérel I. Boucherez J. Thibaud J.B. Sentenac H. J. Biol. Chem. 2001; 276: 3215-3221Abstract Full Text Full Text PDF PubMed Scopus (185) Google Scholar, 20.Xicluna J. Lacombe B. Dreyer I. Alcon C. Jeanguenin L. Sentenac H. Thibaud J.B. Chérel I. J. Biol. Chem. 2007; 282: 486-494Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar, 21.Naso A. Dreyer I. Pedemonte L. Testa I. Gomez-Porras J.L. Usai C. Mueller-Rueber B. Diaspro A. Gambale F. Picco C. Biophys. J. 2009; 96: 4063-4074Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar, 22.Dreyer I. Porée F. Schneider A. Mittelstädt J. Bertl A. Sentenac H. Thibaud J.B. Mueller-Roeber B. Biophys. J. 2004; 87: 858-872Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar, 23.Naso A. Montisci R. Gambale F. Picco C. Biophys. J. 2006; 91: 3673-3683Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar, 24.Formentin E. Varotto S. Costa A. Downey P. Bregante M. Naso A. Picco C. Gambale F. Lo Schiavo F. FEBS Lett. 2004; 573: 61-67Crossref PubMed Scopus (25) Google Scholar, 25.Lebaudy A. Hosy E. Simonneau T. Sentenac H. Thibaud J.B. Dreyer I. Plant J. 2008; 54: 1076-1082Crossref PubMed Scopus (54) Google Scholar, 26.Lebaudy A. Vavasseur A. Hosy E. Dreyer I. Leonhardt N. Thibaud J.B. Véry A.A. Simonneau T. Sentenac H. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 5271-5276Crossref PubMed Scopus (123) Google Scholar, 27.Duby G. Hosy E. Fizames C. Alcon C. Costa A. Sentenac H. Thibaud J.B. Plant J. 2008; 53: 115-123Crossref PubMed Scopus (95) Google Scholar, 28.Jeanguenin L. Lebaudy A. Xicluna J. Alcon C. Hosy E. Duby G. Michard E. Lacombe B. Dreyer I. Thibaud J.B. Plant Signal. Behav. 2008; 3: 622-625Crossref PubMed Scopus (26) Google Scholar, 29.Reintanz B. Szyroki A. Ivashikina N. Ache P. Godde M. Becker D. Palme K. Hedrich R. Proc. Natl. Acad. Sci. U.S.A. 2002; 99: 4079-4084Crossref PubMed Scopus (180) Google Scholar, 30.Bregante M. Yang Y. Formentin E. Carpaneto A. Schroeder J.I. Gambale F. Lo Schiavo F. Costa A. Plant Mol. Biol. 2008; 66: 61-72Crossref PubMed Scopus (26) Google Scholar). As in animal cells, where the diversity of voltage-gated K+ channels arises from the formation of heteromultimeric channels with properties distinct from those of their parent homomultimers (31.Isacoff E.Y. Jan Y.N. Jan L.Y. Nature. 1990; 345: 530-534Crossref PubMed Scopus (377) Google Scholar), heteromerization could potentially yield in plant cells a large diversity of channels being distinctly sensitive to regulatory stimuli. In animal Shaker channel subunits, a domain located in the N-terminal region contributes to discriminating compatible and incompatible channel subunits (32.Xu J. Yu W. Jan Y.N. Jan L.Y. Li M. J. Biol. Chem. 1995; 270: 24761-24768Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar). In contrast, in plant Shaker-like channels, such discrimination involves the cytoplasmic C terminus (22.Dreyer I. Porée F. Schneider A. Mittelstädt J. Bertl A. Sentenac H. Thibaud J.B. Mueller-Roeber B. Biophys. J. 2004; 87: 858-872Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar, 33.Daram P. Urbach S. Gaymard F. Sentenac H. Chérel I. EMBO J. 1997; 16: 3455-3463Crossref PubMed Scopus (114) Google Scholar, 34.Ehrhardt T. Zimmermann S. Müller-Röber B. FEBS Lett. 1997; 409: 166-170Crossref PubMed Scopus (70) Google Scholar, 35.Urbach S. Chérel I. Sentenac H. Gaymard F. Plant J. 2000; 23: 527-538Crossref PubMed Google Scholar).In Arabidopsis, the Shaker-like K+ channel family comprises nine members, and among them, six are expressed in guard cells. Only one gene (GORK) encodes the outward-rectifying K+ conductance (36.Hosy E. Vavasseur A. Mouline K. Dreyer I. Gaymard F. Porée F. Boucherez J. Lebaudy A. Bouchez D. Véry A.A. Simonneau T. Thibaud J.B. Sentenac H. Proc. Natl. Acad. Sci. U.S.A. 2003; 100: 5549-5554Crossref PubMed Scopus (319) Google Scholar), whereas five genes (KAT1, KAT2, AKT1, AKT2, and AtKC1) encode inward-rectifying K+ channel subunits. Among these, KAT1 and KAT2 are predominantly expressed, whereas AKT2, AKT1, and AtKC1 are expressed only at lower levels (37.Szyroki A. Ivashikina N. Dietrich P. Roelfsema M.R. Ache P. Reintanz B. Deeken R. Godde M. Felle H. Steinmeyer R. Palme K. Hedrich R. Proc. Natl. Acad. Sci. U.S.A. 2001; 98: 2917-2921Crossref PubMed Scopus (197) Google Scholar, 38.Ivashikina N. Deeken R. Fischer S. Ache P. Hedrich R. J. Gen. Physiol. 2005; 125: 483-492Crossref PubMed Scopus (56) Google Scholar, 39.Leonhardt N. Kwak J.M. Robert N. Waner D. Leonhardt G. Schroeder J.I. Plant Cell. 2004; 16: 596-615Crossref PubMed Scopus (458) Google Scholar). Comparison of the amino acid sequence of KAT1 and KAT2 revealed that they share an identity of 85% within the region from the first residue to the end of the putative cyclic nucleotide-binding domain. The S4 segments of both channels are identical, and the P domain of KAT2 differs from that of KAT1 only by a single residue. Yeast two-hybrid interaction tests and coexpression experiments in Xenopus oocytes have already demonstrated that KAT1 and KAT2 subunits have the potential to interact and to form heteromeric channels (19.Pilot G. Lacombe B. Gaymard F. Chérel I. Boucherez J. Thibaud J.B. Sentenac H. J. Biol. Chem. 2001; 276: 3215-3221Abstract Full Text Full Text PDF PubMed Scopus (185) Google Scholar). However, it is not known whether they show any preference for homomeric or heteromeric assembly as has been reported for AtKC1 and AKT1 G. Hosy E. Fizames C. Alcon C. Costa A. Sentenac H. Thibaud J.B. Plant J. 2008; 53: 115-123Crossref PubMed Scopus (95) Google Scholar) and for KAT2 and J. Lacombe B. Dreyer I. Alcon C. Jeanguenin L. Sentenac H. Thibaud J.B. Chérel I. J. Biol. Chem. 2007; 282: 486-494Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar). we the of KAT1 and KAT2 and of heteromeric KAT1-KAT2 channels of and with those of channels formed by assembly and with those of native inward-rectifying K+ channels in Arabidopsis guard cells. evidence that, in as as in assembly of heteromeric KAT1-KAT2 channels is that of homomeric KAT1 and KAT2 channels, the native inward conductance in Arabidopsis guard cells mainly on channels made of two KAT1 and two KAT2 subunits. IntroductionStomata are microscopic pores in the plant leaf epidermis that allow both diffusion of atmospheric CO2 toward the inner photosynthetic tissues and water vapor loss by transpiration. Regulation of stomatal aperture allows plants to cope with the conflicting needs of enabling CO2 entry for photosynthesis and of preventing excessive water loss and desiccation. Stomatal movement results from a change in turgor of the two guard cells surrounding the pore. An increase or decrease in turgor opens or closes the stoma, respectively. This osmoregulation process involves K+ transport into and from the guard cells, which are mediated mainly by potassium channels in the plasma membrane belonging to the Shaker family (1.Lebaudy A. Véry A.A. Sentenac H. FEBS Lett. 2007; 581: 2357-2366Crossref PubMed Scopus (241) Google Scholar, 2.Ward J.M. Mäser P. Schroeder J.I. Annu. Rev. Physiol. 2009; 71: 59-82Crossref PubMed Scopus (275) Google Scholar). These potassium channels were found to play pleiotropic roles in guard cells, improving stomatal reactivity to external or internal signals (light, CO2 availability, or evaporative demand) and thus enhancing the ability of the plant to adapt to fluctuating and/or stressing natural environments (1.Lebaudy A. Véry A.A. Sentenac H. FEBS Lett. 2007; 581: 2357-2366Crossref PubMed Scopus (241) Google Scholar).Plant Shaker-like K+ channels are tetrameric proteins built of four α-subunits. Each subunit consists of a hydrophobic core flanked by cytosolic N- and C-terminal regions. The hydrophobic core is composed of six transmembrane segments (S1–S6). The loop between S5 and S6 (P domain) contributes to the permeation pathway of the channel and carries the hallmark GYG(D/E) motif of highly K+-selective channels. The fourth transmembrane segment (S4) contains positively charged amino acids and is involved in the voltage-sensing process of the Shaker-like K+ channels. Hyperpolarization-activated channels mediate inward K+ currents, and depolarization- activated ones mediate outward K+ currents (3.Dreyer I. Blatt M.R. Trends Plant Sci. 2009; 14: 383-390Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar). More generally, the activity of Shaker-like K+ channels is regulated at both the transcriptional and post-translational levels. Large variations in transcript levels have been observed in response to different environmental and hormonal factors such as light, abscisic acid, auxin, and salt stress (4.Véry A.A. Sentenac H. Annu. Rev. Plant Biol. 2003; 54: 575-603Crossref PubMed Scopus (454) Google Scholar). At the post-translational level, channel activity is controlled by intracellular factors such as H+ (5.Lacombe B. Pilot G. Gaymard F. Sentenac H. Thibaud J.B. FEBS Lett. 2000; 466: 351-354Crossref PubMed Scopus (72) Google Scholar, 6.Lacombe B. Pilot G. Michard E. Gaymard F. Sentenac H. Thibaud J.B. Plant Cell. 2000; 12: 837-851PubMed Google Scholar) and cyclic nucleotides (7.Hoshi T. J. Gen. Physiol. 1995; 105: 309-328Crossref PubMed Scopus (195) Google Scholar, 8.Gaymard F. Cerutti M. Horeau C. Lemaillet G. Urbach S. Ravallec M. Devauchelle G. Sentenac H. Thibaud J.B. J. Biol. Chem. 1996; 271: 22863-22870Abstract Full Text Full Text PDF PubMed Scopus (144) Google Scholar). In addition, there is strong evidence that also interacting regulatory proteins, e.g. kinases and phosphatases, dynamically modify channel activity (9.Michard E. Dreyer I. Lacombe B. Sentenac H. Thibaud J.B. Plant J. 2005; 44: 783-797Crossref PubMed Scopus (72) Google Scholar, 10.Michard E. Lacombe B. Porée F. Mueller-Roeber B. Sentenac H. Thibaud J.B. Dreyer I. J. Gen. Physiol. 2005; 126: 605-617Crossref PubMed Scopus (47) Google Scholar, 11.Xu J. Li H.D. Chen L.Q. Wang Y. Liu L.L. He L. Wu W.H. Cell. 2006; 125: 1347-1360Abstract Full Text Full Text PDF PubMed Scopus (715) Google Scholar, 12.Li L. Kim B.G. Cheong Y.H. Pandey G.K. Luan S. Proc. Natl. Acad. Sci. U.S.A. 2006; 103: 12625-12630Crossref PubMed Scopus (334) Google Scholar, 13.Luan S. Trends Plant Sci. 2009; 14: 37-42Abstract Full Text Full Text PDF PubMed Scopus (399) Google Scholar, 14.Luan S. Lan W. Chul Lee S. Curr. Opin. Plant Biol. 2009; 12: 339-346Crossref PubMed Scopus (150) Google Scholar, 15.Geiger D. Becker D. Vosloh D. Gambale F. Palme K. Rehers M. Anschuetz U. Dreyer I. Kudla J. Hedrich R. J. Biol. Chem. 2009; 284: 21288-21295Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar). Interestingly, the tetrameric structure of the channels provides another level of control of their functional properties. A functional channel can be formed not only by the assembly of four identical subunits (homomeric channels) but also by polypeptides encoded by different Shaker-like K+ channel genes (15.Geiger D. Becker D. Vosloh D. Gambale F. Palme K. Rehers M. Anschuetz U. Dreyer I. Kudla J. Hedrich R. J. Biol. Chem. 2009; 284: 21288-21295Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, 16.Dreyer I. Antunes S. Hoshi T. Müller-Röber B. Palme K. Pongs O. Reintanz B. Hedrich R. Biophys. J. 1997; 72: 2143-2150Abstract Full Text PDF PubMed Scopus (143) Google Scholar, 17.Baizabal-Aguirre V.M. Clemens S. Uozumi N. Schroeder J.I. J. Membr. Biol. 1999; 167: 119-125Crossref PubMed Scopus (58) Google Scholar, 18.Ache P. Becker D. Deeken R. Dreyer I. Weber H. Fromm J. Hedrich R. Plant J. 2001; 27: 571-580Crossref PubMed Google Scholar, 19.Pilot G. Lacombe B. Gaymard F. Chérel I. Boucherez J. Thibaud J.B. Sentenac H. J. Biol. Chem. 2001; 276: 3215-3221Abstract Full Text Full Text PDF PubMed Scopus (185) Google Scholar, 20.Xicluna J. Lacombe B. Dreyer I. Alcon C. Jeanguenin L. Sentenac H. Thibaud J.B. Chérel I. J. Biol. Chem. 2007; 282: 486-494Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar, 21.Naso A. Dreyer I. Pedemonte L. Testa I. Gomez-Porras J.L. Usai C. Mueller-Rueber B. Diaspro A. Gambale F. Picco C. Biophys. J. 2009; 96: 4063-4074Abstract Full Text Full Text PDF PubMed Scopus (21) Google Scholar, 22.Dreyer I. Porée F. Schneider A. Mittelstädt J. Bertl A. Sentenac H. Thibaud J.B. Mueller-Roeber B. Biophys. J. 2004; 87: 858-872Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar, 23.Naso A. Montisci R. Gambale F. Picco C. Biophys. J. 2006; 91: 3673-3683Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar, 24.Formentin E. Varotto S. Costa A. Downey P. Bregante M. Naso A. Picco C. Gambale F. Lo Schiavo F. FEBS Lett. 2004; 573: 61-67Crossref PubMed Scopus (25) Google Scholar, 25.Lebaudy A. Hosy E. Simonneau T. Sentenac H. Thibaud J.B. Dreyer I. Plant J. 2008; 54: 1076-1082Crossref PubMed Scopus (54) Google Scholar, 26.Lebaudy A. Vavasseur A. Hosy E. Dreyer I. Leonhardt N. Thibaud J.B. Véry A.A. Simonneau T. Sentenac H. Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 5271-5276Crossref PubMed Scopus (123) Google Scholar, 27.Duby G. Hosy E. Fizames C. Alcon C. Costa A. Sentenac H. Thibaud J.B. Plant J. 2008; 53: 115-123Crossref PubMed Scopus (95) Google Scholar, 28.Jeanguenin L. Lebaudy A. Xicluna J. Alcon C. Hosy E. Duby G. Michard E. Lacombe B. Dreyer I. Thibaud J.B. Plant Signal. Behav. 2008; 3: 622-625Crossref PubMed Scopus (26) Google Scholar, 29.Reintanz B. Szyroki A. Ivashikina N. Ache P. Godde M. Becker D. Palme K. Hedrich R. Proc. Natl. Acad. Sci. U.S.A. 2002; 99: 4079-4084Crossref PubMed Scopus (180) Google Scholar, 30.Bregante M. Yang Y. Formentin E. Carpaneto A. Schroeder J.I. Gambale F. Lo Schiavo F. Costa A. Plant Mol. Biol. 2008; 66: 61-72Crossref PubMed Scopus (26) Google Scholar). As in animal cells, where the diversity of voltage-gated K+ channels arises from the formation of heteromultimeric channels with properties distinct from those of their parent homomultimers (31.Isacoff E.Y. Jan Y.N. Jan L.Y. Nature. 1990; 345: 530-534Crossref PubMed Scopus (377) Google Scholar), heteromerization could potentially yield in plant cells a large diversity of channels being distinctly sensitive to regulatory stimuli. In animal Shaker channel subunits, a domain located in the N-terminal region contributes to discriminating compatible and incompatible channel subunits (32.Xu J. Yu W. Jan Y.N. Jan L.Y. Li M. J. Biol. Chem. 1995; 270: 24761-24768Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar). In contrast, in plant Shaker-like channels, such discrimination involves the cytoplasmic C terminus (22.Dreyer I. Porée F. Schneider A. Mittelstädt J. Bertl A. Sentenac H. Thibaud J.B. Mueller-Roeber B. Biophys. J. 2004; 87: 858-872Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar, 33.Daram P. Urbach S. Gaymard F. Sentenac H. Chérel I. EMBO J. 1997; 16: 3455-3463Crossref PubMed Scopus (114) Google Scholar, 34.Ehrhardt T. Zimmermann S. Müller-Röber B. FEBS Lett. 1997; 409: 166-170Crossref PubMed Scopus (70) Google Scholar, 35.Urbach S. Chérel I. Sentenac H. Gaymard F. Plant J. 2000; 23: 527-538Crossref PubMed Google Scholar).In Arabidopsis, the Shaker-like K+ channel family comprises nine members, and among them, six are expressed in guard cells. Only one gene (GORK) encodes the outward-rectifying K+ conductance (36.Hosy E. Vavasseur A. Mouline K. Dreyer I. Gaymard F. Porée F. Boucherez J. Lebaudy A. Bouchez D. Véry A.A. Simonneau T. Thibaud J.B. Sentenac H. Proc. Natl. Acad. Sci. U.S.A. 2003; 100: 5549-5554Crossref PubMed Scopus (319) Google Scholar), whereas five genes (KAT1, KAT2, AKT1, AKT2, and AtKC1) encode inward-rectifying K+ channel subunits. Among these, KAT1 and KAT2 are predominantly expressed, whereas AKT2, AKT1, and AtKC1 are expressed only at lower levels (37.Szyroki A. Ivashikina N. Dietrich P. Roelfsema M.R. Ache P. Reintanz B. Deeken R. Godde M. Felle H. Steinmeyer R. Palme K. Hedrich R. Proc. Natl. Acad. Sci. U.S.A. 2001; 98: 2917-2921Crossref PubMed Scopus (197) Google Scholar, 38.Ivashikina N. Deeken R. Fischer S. Ache P. Hedrich R. J. Gen. Physiol. 2005; 125: 483-492Crossref PubMed Scopus (56) Google Scholar, 39.Leonhardt N. Kwak J.M. Robert N. Waner D. Leonhardt G. Schroeder J.I. Plant Cell. 2004; 16: 596-615Crossref PubMed Scopus (458) Google Scholar). Comparison of the amino acid sequence of KAT1 and KAT2 revealed that they share an identity of 85% within the region from the first residue to the end of the putative cyclic nucleotide-binding domain. The S4 segments of both channels are identical, and the P domain of KAT2 differs from that of KAT1 only by a single residue. Yeast two-hybrid interaction tests and coexpression experiments in Xenopus oocytes have already demonstrated that KAT1 and KAT2 subunits have the potential to interact and to form heteromeric channels (19.Pilot G. Lacombe B. Gaymard F. Chérel I. Boucherez J. Thibaud J.B. Sentenac H. J. Biol. Chem. 2001; 276: 3215-3221Abstract Full Text Full Text PDF PubMed Scopus (185) Google Scholar). However, it is not known whether they show any preference for homomeric or heteromeric assembly as has been reported for AtKC1 and AKT1 G. Hosy E. Fizames C. Alcon C. Costa A. Sentenac H. Thibaud J.B. Plant J. 2008; 53: 115-123Crossref PubMed Scopus (95) Google Scholar) and for KAT2 and J. Lacombe B. Dreyer I. Alcon C. Jeanguenin L. Sentenac H. Thibaud J.B. Chérel I. J. Biol. Chem. 2007; 282: 486-494Abstract Full Text Full Text PDF PubMed Scopus (61) Google Scholar). we the of KAT1 and KAT2 and of heteromeric KAT1-KAT2 channels of and with those of channels formed by assembly and with those of native inward-rectifying K+ channels in Arabidopsis guard cells. evidence that, in as as in assembly of heteromeric KAT1-KAT2 channels is that of homomeric KAT1 and KAT2 channels, the native inward conductance in Arabidopsis guard cells mainly on channels made of two KAT1 and two KAT2 subunits.
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Nathalie Leonhardt, June M. Kwak, Nadia Robert et al. · The Plant Cell · 2004 · 555 citations · Full text